diff --git a/libc/src/__support/common.h b/libc/src/__support/common.h
--- a/libc/src/__support/common.h
+++ b/libc/src/__support/common.h
@@ -36,16 +36,16 @@
   LLVM_LIBC_FUNCTION_ATTR decltype(__llvm_libc::name)                          \
       __##name##_impl__ __asm__(#name);                                        \
   LLVM_LIBC_DECLARE_DEVICE(__##name##_impl__)                                  \
-  type __##name##_impl__ arglist
+  type __##name##_impl__ arglist noexcept
 // MacOS needs to be excluded because it does not support aliasing.
 #elif defined(LLVM_LIBC_PUBLIC_PACKAGING) && (!defined(__APPLE__))
 #define LLVM_LIBC_FUNCTION(type, name, arglist)                                \
   LLVM_LIBC_FUNCTION_ATTR decltype(__llvm_libc::name)                          \
       __##name##_impl__ __asm__(#name);                                        \
   decltype(__llvm_libc::name) name [[gnu::alias(#name)]];                      \
-  type __##name##_impl__ arglist
+  type __##name##_impl__ arglist noexcept
 #else
-#define LLVM_LIBC_FUNCTION(type, name, arglist) type name arglist
+#define LLVM_LIBC_FUNCTION(type, name, arglist) type name arglist noexcept
 #endif
 
 namespace __llvm_libc {
diff --git a/libc/src/assert/__assert_fail.h b/libc/src/assert/__assert_fail.h
--- a/libc/src/assert/__assert_fail.h
+++ b/libc/src/assert/__assert_fail.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 [[noreturn]] void __assert_fail(const char *assertion, const char *file,
-                                unsigned line, const char *function);
+                                unsigned line, const char *function) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/isalnum.h b/libc/src/ctype/isalnum.h
--- a/libc/src/ctype/isalnum.h
+++ b/libc/src/ctype/isalnum.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int isalnum(int c);
+int isalnum(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/isalpha.h b/libc/src/ctype/isalpha.h
--- a/libc/src/ctype/isalpha.h
+++ b/libc/src/ctype/isalpha.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int isalpha(int c);
+int isalpha(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/isascii.h b/libc/src/ctype/isascii.h
--- a/libc/src/ctype/isascii.h
+++ b/libc/src/ctype/isascii.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int isascii(int c);
+int isascii(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/isblank.h b/libc/src/ctype/isblank.h
--- a/libc/src/ctype/isblank.h
+++ b/libc/src/ctype/isblank.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int isblank(int c);
+int isblank(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/iscntrl.h b/libc/src/ctype/iscntrl.h
--- a/libc/src/ctype/iscntrl.h
+++ b/libc/src/ctype/iscntrl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int iscntrl(int c);
+int iscntrl(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/isdigit.h b/libc/src/ctype/isdigit.h
--- a/libc/src/ctype/isdigit.h
+++ b/libc/src/ctype/isdigit.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int isdigit(int c);
+int isdigit(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/isgraph.h b/libc/src/ctype/isgraph.h
--- a/libc/src/ctype/isgraph.h
+++ b/libc/src/ctype/isgraph.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int isgraph(int c);
+int isgraph(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/islower.h b/libc/src/ctype/islower.h
--- a/libc/src/ctype/islower.h
+++ b/libc/src/ctype/islower.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int islower(int c);
+int islower(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/isprint.h b/libc/src/ctype/isprint.h
--- a/libc/src/ctype/isprint.h
+++ b/libc/src/ctype/isprint.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int isprint(int c);
+int isprint(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/ispunct.h b/libc/src/ctype/ispunct.h
--- a/libc/src/ctype/ispunct.h
+++ b/libc/src/ctype/ispunct.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int ispunct(int c);
+int ispunct(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/isspace.h b/libc/src/ctype/isspace.h
--- a/libc/src/ctype/isspace.h
+++ b/libc/src/ctype/isspace.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int isspace(int c);
+int isspace(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/isupper.h b/libc/src/ctype/isupper.h
--- a/libc/src/ctype/isupper.h
+++ b/libc/src/ctype/isupper.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int isupper(int c);
+int isupper(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/isxdigit.h b/libc/src/ctype/isxdigit.h
--- a/libc/src/ctype/isxdigit.h
+++ b/libc/src/ctype/isxdigit.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int isxdigit(int c);
+int isxdigit(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/toascii.h b/libc/src/ctype/toascii.h
--- a/libc/src/ctype/toascii.h
+++ b/libc/src/ctype/toascii.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int toascii(int c);
+int toascii(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/tolower.h b/libc/src/ctype/tolower.h
--- a/libc/src/ctype/tolower.h
+++ b/libc/src/ctype/tolower.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int tolower(int c);
+int tolower(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/ctype/toupper.h b/libc/src/ctype/toupper.h
--- a/libc/src/ctype/toupper.h
+++ b/libc/src/ctype/toupper.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int toupper(int c);
+int toupper(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/dirent/closedir.h b/libc/src/dirent/closedir.h
--- a/libc/src/dirent/closedir.h
+++ b/libc/src/dirent/closedir.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int closedir(::DIR *dir);
+int closedir(::DIR *dir) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/dirent/dirfd.h b/libc/src/dirent/dirfd.h
--- a/libc/src/dirent/dirfd.h
+++ b/libc/src/dirent/dirfd.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int dirfd(::DIR *dir);
+int dirfd(::DIR *dir) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/dirent/opendir.h b/libc/src/dirent/opendir.h
--- a/libc/src/dirent/opendir.h
+++ b/libc/src/dirent/opendir.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-::DIR *opendir(const char *name);
+::DIR *opendir(const char *name) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/dirent/readdir.h b/libc/src/dirent/readdir.h
--- a/libc/src/dirent/readdir.h
+++ b/libc/src/dirent/readdir.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-struct ::dirent *readdir(DIR *dir);
+struct ::dirent *readdir(DIR *dir) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fcntl/creat.h b/libc/src/fcntl/creat.h
--- a/libc/src/fcntl/creat.h
+++ b/libc/src/fcntl/creat.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int creat(const char *path, int mode);
+int creat(const char *path, int mode) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fcntl/open.h b/libc/src/fcntl/open.h
--- a/libc/src/fcntl/open.h
+++ b/libc/src/fcntl/open.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int open(const char *path, int flags, ...);
+int open(const char *path, int flags, ...) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fcntl/openat.h b/libc/src/fcntl/openat.h
--- a/libc/src/fcntl/openat.h
+++ b/libc/src/fcntl/openat.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int openat(int dfd, const char *path, int flags, ...);
+int openat(int dfd, const char *path, int flags, ...) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/feclearexcept.h b/libc/src/fenv/feclearexcept.h
--- a/libc/src/fenv/feclearexcept.h
+++ b/libc/src/fenv/feclearexcept.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int feclearexcept(int);
+int feclearexcept(int) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/fedisableexcept.h b/libc/src/fenv/fedisableexcept.h
--- a/libc/src/fenv/fedisableexcept.h
+++ b/libc/src/fenv/fedisableexcept.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int fedisableexcept(int);
+int fedisableexcept(int) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/feenableexcept.h b/libc/src/fenv/feenableexcept.h
--- a/libc/src/fenv/feenableexcept.h
+++ b/libc/src/fenv/feenableexcept.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int feenableexcept(int);
+int feenableexcept(int) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/fegetenv.h b/libc/src/fenv/fegetenv.h
--- a/libc/src/fenv/fegetenv.h
+++ b/libc/src/fenv/fegetenv.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fegetenv(fenv_t *);
+int fegetenv(fenv_t *) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/fegetexcept.h b/libc/src/fenv/fegetexcept.h
--- a/libc/src/fenv/fegetexcept.h
+++ b/libc/src/fenv/fegetexcept.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int fegetexcept();
+int fegetexcept() noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/fegetexceptflag.h b/libc/src/fenv/fegetexceptflag.h
--- a/libc/src/fenv/fegetexceptflag.h
+++ b/libc/src/fenv/fegetexceptflag.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fegetexceptflag(fexcept_t *, int excepts);
+int fegetexceptflag(fexcept_t *, int excepts) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/fegetround.h b/libc/src/fenv/fegetround.h
--- a/libc/src/fenv/fegetround.h
+++ b/libc/src/fenv/fegetround.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int fegetround();
+int fegetround() noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/feholdexcept.h b/libc/src/fenv/feholdexcept.h
--- a/libc/src/fenv/feholdexcept.h
+++ b/libc/src/fenv/feholdexcept.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int feholdexcept(fenv_t *);
+int feholdexcept(fenv_t *) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/feraiseexcept.h b/libc/src/fenv/feraiseexcept.h
--- a/libc/src/fenv/feraiseexcept.h
+++ b/libc/src/fenv/feraiseexcept.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int feraiseexcept(int);
+int feraiseexcept(int) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/fesetenv.h b/libc/src/fenv/fesetenv.h
--- a/libc/src/fenv/fesetenv.h
+++ b/libc/src/fenv/fesetenv.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fesetenv(const fenv_t *);
+int fesetenv(const fenv_t *) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/fesetexceptflag.h b/libc/src/fenv/fesetexceptflag.h
--- a/libc/src/fenv/fesetexceptflag.h
+++ b/libc/src/fenv/fesetexceptflag.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fesetexceptflag(const fexcept_t *, int excepts);
+int fesetexceptflag(const fexcept_t *, int excepts) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/fesetround.h b/libc/src/fenv/fesetround.h
--- a/libc/src/fenv/fesetround.h
+++ b/libc/src/fenv/fesetround.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int fesetround(int);
+int fesetround(int) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/fetestexcept.h b/libc/src/fenv/fetestexcept.h
--- a/libc/src/fenv/fetestexcept.h
+++ b/libc/src/fenv/fetestexcept.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int fetestexcept(int);
+int fetestexcept(int) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/fenv/feupdateenv.h b/libc/src/fenv/feupdateenv.h
--- a/libc/src/fenv/feupdateenv.h
+++ b/libc/src/fenv/feupdateenv.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int feupdateenv(const fenv_t *);
+int feupdateenv(const fenv_t *) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/inttypes/imaxabs.h b/libc/src/inttypes/imaxabs.h
--- a/libc/src/inttypes/imaxabs.h
+++ b/libc/src/inttypes/imaxabs.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-intmax_t imaxabs(intmax_t j);
+intmax_t imaxabs(intmax_t j) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/inttypes/imaxdiv.h b/libc/src/inttypes/imaxdiv.h
--- a/libc/src/inttypes/imaxdiv.h
+++ b/libc/src/inttypes/imaxdiv.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-imaxdiv_t imaxdiv(intmax_t x, intmax_t y);
+imaxdiv_t imaxdiv(intmax_t x, intmax_t y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/inttypes/strtoimax.h b/libc/src/inttypes/strtoimax.h
--- a/libc/src/inttypes/strtoimax.h
+++ b/libc/src/inttypes/strtoimax.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 intmax_t strtoimax(const char *__restrict str, char **__restrict str_end,
-                   int base);
+                   int base) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/inttypes/strtoumax.h b/libc/src/inttypes/strtoumax.h
--- a/libc/src/inttypes/strtoumax.h
+++ b/libc/src/inttypes/strtoumax.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 uintmax_t strtoumax(const char *__restrict str, char **__restrict str_end,
-                    int base);
+                    int base) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/acosf.h b/libc/src/math/acosf.h
--- a/libc/src/math/acosf.h
+++ b/libc/src/math/acosf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float acosf(float x);
+float acosf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/asin.h b/libc/src/math/asin.h
--- a/libc/src/math/asin.h
+++ b/libc/src/math/asin.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double asin(double x);
+double asin(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/asinf.h b/libc/src/math/asinf.h
--- a/libc/src/math/asinf.h
+++ b/libc/src/math/asinf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float asinf(float x);
+float asinf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/atanf.h b/libc/src/math/atanf.h
--- a/libc/src/math/atanf.h
+++ b/libc/src/math/atanf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float atanf(float x);
+float atanf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/atanhf.h b/libc/src/math/atanhf.h
--- a/libc/src/math/atanhf.h
+++ b/libc/src/math/atanhf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float atanhf(float x);
+float atanhf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/ceil.h b/libc/src/math/ceil.h
--- a/libc/src/math/ceil.h
+++ b/libc/src/math/ceil.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double ceil(double x);
+double ceil(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/ceilf.h b/libc/src/math/ceilf.h
--- a/libc/src/math/ceilf.h
+++ b/libc/src/math/ceilf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float ceilf(float x);
+float ceilf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/ceill.h b/libc/src/math/ceill.h
--- a/libc/src/math/ceill.h
+++ b/libc/src/math/ceill.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double ceill(long double x);
+long double ceill(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/copysign.h b/libc/src/math/copysign.h
--- a/libc/src/math/copysign.h
+++ b/libc/src/math/copysign.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double copysign(double x, double y);
+double copysign(double x, double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/copysignf.h b/libc/src/math/copysignf.h
--- a/libc/src/math/copysignf.h
+++ b/libc/src/math/copysignf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float copysignf(float x, float y);
+float copysignf(float x, float y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/copysignl.h b/libc/src/math/copysignl.h
--- a/libc/src/math/copysignl.h
+++ b/libc/src/math/copysignl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double copysignl(long double x, long double y);
+long double copysignl(long double x, long double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/cos.h b/libc/src/math/cos.h
--- a/libc/src/math/cos.h
+++ b/libc/src/math/cos.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double cos(double x);
+double cos(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/cosf.h b/libc/src/math/cosf.h
--- a/libc/src/math/cosf.h
+++ b/libc/src/math/cosf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float cosf(float x);
+float cosf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/coshf.h b/libc/src/math/coshf.h
--- a/libc/src/math/coshf.h
+++ b/libc/src/math/coshf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float coshf(float x);
+float coshf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/exp10f.h b/libc/src/math/exp10f.h
--- a/libc/src/math/exp10f.h
+++ b/libc/src/math/exp10f.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float exp10f(float x);
+float exp10f(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/exp2f.h b/libc/src/math/exp2f.h
--- a/libc/src/math/exp2f.h
+++ b/libc/src/math/exp2f.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float exp2f(float x);
+float exp2f(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/expf.h b/libc/src/math/expf.h
--- a/libc/src/math/expf.h
+++ b/libc/src/math/expf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float expf(float x);
+float expf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/expm1f.h b/libc/src/math/expm1f.h
--- a/libc/src/math/expm1f.h
+++ b/libc/src/math/expm1f.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float expm1f(float x);
+float expm1f(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fabs.h b/libc/src/math/fabs.h
--- a/libc/src/math/fabs.h
+++ b/libc/src/math/fabs.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double fabs(double x);
+double fabs(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fabsf.h b/libc/src/math/fabsf.h
--- a/libc/src/math/fabsf.h
+++ b/libc/src/math/fabsf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float fabsf(float x);
+float fabsf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fabsl.h b/libc/src/math/fabsl.h
--- a/libc/src/math/fabsl.h
+++ b/libc/src/math/fabsl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double fabsl(long double x);
+long double fabsl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fdim.h b/libc/src/math/fdim.h
--- a/libc/src/math/fdim.h
+++ b/libc/src/math/fdim.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double fdim(double x, double y);
+double fdim(double x, double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fdimf.h b/libc/src/math/fdimf.h
--- a/libc/src/math/fdimf.h
+++ b/libc/src/math/fdimf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float fdimf(float x, float y);
+float fdimf(float x, float y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fdiml.h b/libc/src/math/fdiml.h
--- a/libc/src/math/fdiml.h
+++ b/libc/src/math/fdiml.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double fdiml(long double x, long double y);
+long double fdiml(long double x, long double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/floor.h b/libc/src/math/floor.h
--- a/libc/src/math/floor.h
+++ b/libc/src/math/floor.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double floor(double x);
+double floor(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/floorf.h b/libc/src/math/floorf.h
--- a/libc/src/math/floorf.h
+++ b/libc/src/math/floorf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float floorf(float x);
+float floorf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/floorl.h b/libc/src/math/floorl.h
--- a/libc/src/math/floorl.h
+++ b/libc/src/math/floorl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double floorl(long double x);
+long double floorl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fma.h b/libc/src/math/fma.h
--- a/libc/src/math/fma.h
+++ b/libc/src/math/fma.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double fma(double x, double y, double z);
+double fma(double x, double y, double z) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fmaf.h b/libc/src/math/fmaf.h
--- a/libc/src/math/fmaf.h
+++ b/libc/src/math/fmaf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float fmaf(float x, float y, float z);
+float fmaf(float x, float y, float z) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fmax.h b/libc/src/math/fmax.h
--- a/libc/src/math/fmax.h
+++ b/libc/src/math/fmax.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double fmax(double x, double y);
+double fmax(double x, double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fmaxf.h b/libc/src/math/fmaxf.h
--- a/libc/src/math/fmaxf.h
+++ b/libc/src/math/fmaxf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float fmaxf(float x, float y);
+float fmaxf(float x, float y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fmaxl.h b/libc/src/math/fmaxl.h
--- a/libc/src/math/fmaxl.h
+++ b/libc/src/math/fmaxl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double fmaxl(long double x, long double y);
+long double fmaxl(long double x, long double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fmin.h b/libc/src/math/fmin.h
--- a/libc/src/math/fmin.h
+++ b/libc/src/math/fmin.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double fmin(double x, double y);
+double fmin(double x, double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fminf.h b/libc/src/math/fminf.h
--- a/libc/src/math/fminf.h
+++ b/libc/src/math/fminf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float fminf(float x, float y);
+float fminf(float x, float y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fminl.h b/libc/src/math/fminl.h
--- a/libc/src/math/fminl.h
+++ b/libc/src/math/fminl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double fminl(long double x, long double y);
+long double fminl(long double x, long double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fmod.h b/libc/src/math/fmod.h
--- a/libc/src/math/fmod.h
+++ b/libc/src/math/fmod.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double fmod(double x, double y);
+double fmod(double x, double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/fmodf.h b/libc/src/math/fmodf.h
--- a/libc/src/math/fmodf.h
+++ b/libc/src/math/fmodf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float fmodf(float x, float y);
+float fmodf(float x, float y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/frexp.h b/libc/src/math/frexp.h
--- a/libc/src/math/frexp.h
+++ b/libc/src/math/frexp.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double frexp(double x, int *exp);
+double frexp(double x, int *exp) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/frexpf.h b/libc/src/math/frexpf.h
--- a/libc/src/math/frexpf.h
+++ b/libc/src/math/frexpf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float frexpf(float x, int *exp);
+float frexpf(float x, int *exp) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/frexpl.h b/libc/src/math/frexpl.h
--- a/libc/src/math/frexpl.h
+++ b/libc/src/math/frexpl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double frexpl(long double x, int *exp);
+long double frexpl(long double x, int *exp) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/hypot.h b/libc/src/math/hypot.h
--- a/libc/src/math/hypot.h
+++ b/libc/src/math/hypot.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double hypot(double x, double y);
+double hypot(double x, double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/hypotf.h b/libc/src/math/hypotf.h
--- a/libc/src/math/hypotf.h
+++ b/libc/src/math/hypotf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float hypotf(float x, float y);
+float hypotf(float x, float y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/ilogb.h b/libc/src/math/ilogb.h
--- a/libc/src/math/ilogb.h
+++ b/libc/src/math/ilogb.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int ilogb(double x);
+int ilogb(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/ilogbf.h b/libc/src/math/ilogbf.h
--- a/libc/src/math/ilogbf.h
+++ b/libc/src/math/ilogbf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int ilogbf(float x);
+int ilogbf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/ilogbl.h b/libc/src/math/ilogbl.h
--- a/libc/src/math/ilogbl.h
+++ b/libc/src/math/ilogbl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int ilogbl(long double x);
+int ilogbl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/ldexp.h b/libc/src/math/ldexp.h
--- a/libc/src/math/ldexp.h
+++ b/libc/src/math/ldexp.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double ldexp(double x, int exp);
+double ldexp(double x, int exp) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/ldexpf.h b/libc/src/math/ldexpf.h
--- a/libc/src/math/ldexpf.h
+++ b/libc/src/math/ldexpf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float ldexpf(float x, int exp);
+float ldexpf(float x, int exp) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/ldexpl.h b/libc/src/math/ldexpl.h
--- a/libc/src/math/ldexpl.h
+++ b/libc/src/math/ldexpl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double ldexpl(long double x, int exp);
+long double ldexpl(long double x, int exp) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/llrint.h b/libc/src/math/llrint.h
--- a/libc/src/math/llrint.h
+++ b/libc/src/math/llrint.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long long llrint(double x);
+long long llrint(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/llrintf.h b/libc/src/math/llrintf.h
--- a/libc/src/math/llrintf.h
+++ b/libc/src/math/llrintf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long long llrintf(float x);
+long long llrintf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/llrintl.h b/libc/src/math/llrintl.h
--- a/libc/src/math/llrintl.h
+++ b/libc/src/math/llrintl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long long llrintl(long double x);
+long long llrintl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/llround.h b/libc/src/math/llround.h
--- a/libc/src/math/llround.h
+++ b/libc/src/math/llround.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long long llround(double x);
+long long llround(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/llroundf.h b/libc/src/math/llroundf.h
--- a/libc/src/math/llroundf.h
+++ b/libc/src/math/llroundf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long long llroundf(float x);
+long long llroundf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/llroundl.h b/libc/src/math/llroundl.h
--- a/libc/src/math/llroundl.h
+++ b/libc/src/math/llroundl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long long llroundl(long double x);
+long long llroundl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/log10f.h b/libc/src/math/log10f.h
--- a/libc/src/math/log10f.h
+++ b/libc/src/math/log10f.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float log10f(float x);
+float log10f(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/log1pf.h b/libc/src/math/log1pf.h
--- a/libc/src/math/log1pf.h
+++ b/libc/src/math/log1pf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float log1pf(float x);
+float log1pf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/log2f.h b/libc/src/math/log2f.h
--- a/libc/src/math/log2f.h
+++ b/libc/src/math/log2f.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float log2f(float x);
+float log2f(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/logb.h b/libc/src/math/logb.h
--- a/libc/src/math/logb.h
+++ b/libc/src/math/logb.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double logb(double x);
+double logb(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/logbf.h b/libc/src/math/logbf.h
--- a/libc/src/math/logbf.h
+++ b/libc/src/math/logbf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float logbf(float x);
+float logbf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/logbl.h b/libc/src/math/logbl.h
--- a/libc/src/math/logbl.h
+++ b/libc/src/math/logbl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double logbl(long double x);
+long double logbl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/logf.h b/libc/src/math/logf.h
--- a/libc/src/math/logf.h
+++ b/libc/src/math/logf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float logf(float x);
+float logf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/lrint.h b/libc/src/math/lrint.h
--- a/libc/src/math/lrint.h
+++ b/libc/src/math/lrint.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long lrint(double x);
+long lrint(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/lrintf.h b/libc/src/math/lrintf.h
--- a/libc/src/math/lrintf.h
+++ b/libc/src/math/lrintf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long lrintf(float x);
+long lrintf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/lrintl.h b/libc/src/math/lrintl.h
--- a/libc/src/math/lrintl.h
+++ b/libc/src/math/lrintl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long lrintl(long double x);
+long lrintl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/lround.h b/libc/src/math/lround.h
--- a/libc/src/math/lround.h
+++ b/libc/src/math/lround.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long lround(double x);
+long lround(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/lroundf.h b/libc/src/math/lroundf.h
--- a/libc/src/math/lroundf.h
+++ b/libc/src/math/lroundf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long lroundf(float x);
+long lroundf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/lroundl.h b/libc/src/math/lroundl.h
--- a/libc/src/math/lroundl.h
+++ b/libc/src/math/lroundl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long lroundl(long double x);
+long lroundl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/modf.h b/libc/src/math/modf.h
--- a/libc/src/math/modf.h
+++ b/libc/src/math/modf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double modf(double x, double *iptr);
+double modf(double x, double *iptr) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/modff.h b/libc/src/math/modff.h
--- a/libc/src/math/modff.h
+++ b/libc/src/math/modff.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float modff(float x, float *iptr);
+float modff(float x, float *iptr) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/modfl.h b/libc/src/math/modfl.h
--- a/libc/src/math/modfl.h
+++ b/libc/src/math/modfl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double modfl(long double x, long double *iptr);
+long double modfl(long double x, long double *iptr) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/nearbyint.h b/libc/src/math/nearbyint.h
--- a/libc/src/math/nearbyint.h
+++ b/libc/src/math/nearbyint.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double nearbyint(double x);
+double nearbyint(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/nearbyintf.h b/libc/src/math/nearbyintf.h
--- a/libc/src/math/nearbyintf.h
+++ b/libc/src/math/nearbyintf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float nearbyintf(float x);
+float nearbyintf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/nearbyintl.h b/libc/src/math/nearbyintl.h
--- a/libc/src/math/nearbyintl.h
+++ b/libc/src/math/nearbyintl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double nearbyintl(long double x);
+long double nearbyintl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/nextafter.h b/libc/src/math/nextafter.h
--- a/libc/src/math/nextafter.h
+++ b/libc/src/math/nextafter.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double nextafter(double x, double y);
+double nextafter(double x, double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/nextafterf.h b/libc/src/math/nextafterf.h
--- a/libc/src/math/nextafterf.h
+++ b/libc/src/math/nextafterf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float nextafterf(float x, float y);
+float nextafterf(float x, float y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/nextafterl.h b/libc/src/math/nextafterl.h
--- a/libc/src/math/nextafterl.h
+++ b/libc/src/math/nextafterl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double nextafterl(long double x, long double y);
+long double nextafterl(long double x, long double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/pow.h b/libc/src/math/pow.h
--- a/libc/src/math/pow.h
+++ b/libc/src/math/pow.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double pow(double x, double y);
+double pow(double x, double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/remainder.h b/libc/src/math/remainder.h
--- a/libc/src/math/remainder.h
+++ b/libc/src/math/remainder.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double remainder(double x, double y);
+double remainder(double x, double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/remainderf.h b/libc/src/math/remainderf.h
--- a/libc/src/math/remainderf.h
+++ b/libc/src/math/remainderf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float remainderf(float x, float y);
+float remainderf(float x, float y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/remainderl.h b/libc/src/math/remainderl.h
--- a/libc/src/math/remainderl.h
+++ b/libc/src/math/remainderl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double remainderl(long double x, long double y);
+long double remainderl(long double x, long double y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/remquo.h b/libc/src/math/remquo.h
--- a/libc/src/math/remquo.h
+++ b/libc/src/math/remquo.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double remquo(double x, double y, int *exp);
+double remquo(double x, double y, int *exp) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/remquof.h b/libc/src/math/remquof.h
--- a/libc/src/math/remquof.h
+++ b/libc/src/math/remquof.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float remquof(float x, float y, int *exp);
+float remquof(float x, float y, int *exp) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/remquol.h b/libc/src/math/remquol.h
--- a/libc/src/math/remquol.h
+++ b/libc/src/math/remquol.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double remquol(long double x, long double y, int *exp);
+long double remquol(long double x, long double y, int *exp) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/rint.h b/libc/src/math/rint.h
--- a/libc/src/math/rint.h
+++ b/libc/src/math/rint.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double rint(double x);
+double rint(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/rintf.h b/libc/src/math/rintf.h
--- a/libc/src/math/rintf.h
+++ b/libc/src/math/rintf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float rintf(float x);
+float rintf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/rintl.h b/libc/src/math/rintl.h
--- a/libc/src/math/rintl.h
+++ b/libc/src/math/rintl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double rintl(long double x);
+long double rintl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/round.h b/libc/src/math/round.h
--- a/libc/src/math/round.h
+++ b/libc/src/math/round.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double round(double x);
+double round(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/roundf.h b/libc/src/math/roundf.h
--- a/libc/src/math/roundf.h
+++ b/libc/src/math/roundf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float roundf(float x);
+float roundf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/roundl.h b/libc/src/math/roundl.h
--- a/libc/src/math/roundl.h
+++ b/libc/src/math/roundl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double roundl(long double x);
+long double roundl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/sin.h b/libc/src/math/sin.h
--- a/libc/src/math/sin.h
+++ b/libc/src/math/sin.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double sin(double x);
+double sin(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/sincosf.h b/libc/src/math/sincosf.h
--- a/libc/src/math/sincosf.h
+++ b/libc/src/math/sincosf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-void sincosf(float x, float *sinx, float *cosx);
+void sincosf(float x, float *sinx, float *cosx) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/sinf.h b/libc/src/math/sinf.h
--- a/libc/src/math/sinf.h
+++ b/libc/src/math/sinf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float sinf(float x);
+float sinf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/sinhf.h b/libc/src/math/sinhf.h
--- a/libc/src/math/sinhf.h
+++ b/libc/src/math/sinhf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float sinhf(float x);
+float sinhf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/sqrt.h b/libc/src/math/sqrt.h
--- a/libc/src/math/sqrt.h
+++ b/libc/src/math/sqrt.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double sqrt(double x);
+double sqrt(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/sqrtf.h b/libc/src/math/sqrtf.h
--- a/libc/src/math/sqrtf.h
+++ b/libc/src/math/sqrtf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float sqrtf(float x);
+float sqrtf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/sqrtl.h b/libc/src/math/sqrtl.h
--- a/libc/src/math/sqrtl.h
+++ b/libc/src/math/sqrtl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double sqrtl(long double x);
+long double sqrtl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/tan.h b/libc/src/math/tan.h
--- a/libc/src/math/tan.h
+++ b/libc/src/math/tan.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double tan(double x);
+double tan(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/tanf.h b/libc/src/math/tanf.h
--- a/libc/src/math/tanf.h
+++ b/libc/src/math/tanf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float tanf(float x);
+float tanf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/tanhf.h b/libc/src/math/tanhf.h
--- a/libc/src/math/tanhf.h
+++ b/libc/src/math/tanhf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float tanhf(float x);
+float tanhf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/trunc.h b/libc/src/math/trunc.h
--- a/libc/src/math/trunc.h
+++ b/libc/src/math/trunc.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double trunc(double x);
+double trunc(double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/truncf.h b/libc/src/math/truncf.h
--- a/libc/src/math/truncf.h
+++ b/libc/src/math/truncf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float truncf(float x);
+float truncf(float x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/math/truncl.h b/libc/src/math/truncl.h
--- a/libc/src/math/truncl.h
+++ b/libc/src/math/truncl.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long double truncl(long double x);
+long double truncl(long double x) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_atfork.h b/libc/src/pthread/pthread_atfork.h
--- a/libc/src/pthread/pthread_atfork.h
+++ b/libc/src/pthread/pthread_atfork.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int pthread_atfork(__atfork_callback_t prepare, __atfork_callback_t parent,
-                   __atfork_callback_t child);
+                   __atfork_callback_t child) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_attr_destroy.h b/libc/src/pthread/pthread_attr_destroy.h
--- a/libc/src/pthread/pthread_attr_destroy.h
+++ b/libc/src/pthread/pthread_attr_destroy.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_attr_destroy(pthread_attr_t *attr);
+int pthread_attr_destroy(pthread_attr_t *attr) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_attr_getdetachstate.h b/libc/src/pthread/pthread_attr_getdetachstate.h
--- a/libc/src/pthread/pthread_attr_getdetachstate.h
+++ b/libc/src/pthread/pthread_attr_getdetachstate.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-int pthread_attr_getdetachstate(const pthread_attr_t *attr, int *detach_state);
+int pthread_attr_getdetachstate(const pthread_attr_t *attr,
+                                int *detach_state) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_attr_getguardsize.h b/libc/src/pthread/pthread_attr_getguardsize.h
--- a/libc/src/pthread/pthread_attr_getguardsize.h
+++ b/libc/src/pthread/pthread_attr_getguardsize.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int pthread_attr_getguardsize(const pthread_attr_t *__restrict attr,
-                              size_t *__restrict guardsize);
+                              size_t *__restrict guardsize) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_attr_getstack.h b/libc/src/pthread/pthread_attr_getstack.h
--- a/libc/src/pthread/pthread_attr_getstack.h
+++ b/libc/src/pthread/pthread_attr_getstack.h
@@ -15,7 +15,7 @@
 
 int pthread_attr_getstack(const pthread_attr_t *__restrict attr,
                           void **__restrict stack,
-                          size_t *__restrict stacksize);
+                          size_t *__restrict stacksize) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_attr_getstacksize.h b/libc/src/pthread/pthread_attr_getstacksize.h
--- a/libc/src/pthread/pthread_attr_getstacksize.h
+++ b/libc/src/pthread/pthread_attr_getstacksize.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int pthread_attr_getstacksize(const pthread_attr_t *__restrict attr,
-                              size_t *__restrict stacksize);
+                              size_t *__restrict stacksize) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_attr_init.h b/libc/src/pthread/pthread_attr_init.h
--- a/libc/src/pthread/pthread_attr_init.h
+++ b/libc/src/pthread/pthread_attr_init.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_attr_init(pthread_attr_t *attr);
+int pthread_attr_init(pthread_attr_t *attr) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_attr_setdetachstate.h b/libc/src/pthread/pthread_attr_setdetachstate.h
--- a/libc/src/pthread/pthread_attr_setdetachstate.h
+++ b/libc/src/pthread/pthread_attr_setdetachstate.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-int pthread_attr_setdetachstate(pthread_attr_t *attr, int detach_state);
+int pthread_attr_setdetachstate(pthread_attr_t *attr,
+                                int detach_state) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_attr_setguardsize.h b/libc/src/pthread/pthread_attr_setguardsize.h
--- a/libc/src/pthread/pthread_attr_setguardsize.h
+++ b/libc/src/pthread/pthread_attr_setguardsize.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
+int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_attr_setstack.h b/libc/src/pthread/pthread_attr_setstack.h
--- a/libc/src/pthread/pthread_attr_setstack.h
+++ b/libc/src/pthread/pthread_attr_setstack.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-int pthread_attr_setstack(pthread_attr_t *attr, void *stack, size_t stacksize);
+int pthread_attr_setstack(pthread_attr_t *attr, void *stack,
+                          size_t stacksize) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_attr_setstacksize.h b/libc/src/pthread/pthread_attr_setstacksize.h
--- a/libc/src/pthread/pthread_attr_setstacksize.h
+++ b/libc/src/pthread/pthread_attr_setstacksize.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_attr_setstacksize(pthread_attr_t *attr, size_t stacksize);
+int pthread_attr_setstacksize(pthread_attr_t *attr, size_t stacksize) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_create.h b/libc/src/pthread/pthread_create.h
--- a/libc/src/pthread/pthread_create.h
+++ b/libc/src/pthread/pthread_create.h
@@ -15,7 +15,7 @@
 
 int pthread_create(pthread_t *__restrict thread,
                    const pthread_attr_t *__restrict attr,
-                   __pthread_start_t func, void *arg);
+                   __pthread_start_t func, void *arg) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_detach.h b/libc/src/pthread/pthread_detach.h
--- a/libc/src/pthread/pthread_detach.h
+++ b/libc/src/pthread/pthread_detach.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_detach(pthread_t thread);
+int pthread_detach(pthread_t thread) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_equal.h b/libc/src/pthread/pthread_equal.h
--- a/libc/src/pthread/pthread_equal.h
+++ b/libc/src/pthread/pthread_equal.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_equal(pthread_t lhs, pthread_t rhs);
+int pthread_equal(pthread_t lhs, pthread_t rhs) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_exit.h b/libc/src/pthread/pthread_exit.h
--- a/libc/src/pthread/pthread_exit.h
+++ b/libc/src/pthread/pthread_exit.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void pthread_exit(void *retval);
+void pthread_exit(void *retval) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_getname_np.h b/libc/src/pthread/pthread_getname_np.h
--- a/libc/src/pthread/pthread_getname_np.h
+++ b/libc/src/pthread/pthread_getname_np.h
@@ -14,7 +14,7 @@
 
 namespace __llvm_libc {
 
-int pthread_getname_np(pthread_t, char *, size_t);
+int pthread_getname_np(pthread_t, char *, size_t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_getspecific.h b/libc/src/pthread/pthread_getspecific.h
--- a/libc/src/pthread/pthread_getspecific.h
+++ b/libc/src/pthread/pthread_getspecific.h
@@ -14,7 +14,7 @@
 
 namespace __llvm_libc {
 
-void *pthread_getspecific(pthread_key_t);
+void *pthread_getspecific(pthread_key_t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_join.h b/libc/src/pthread/pthread_join.h
--- a/libc/src/pthread/pthread_join.h
+++ b/libc/src/pthread/pthread_join.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_join(pthread_t thread, void **retval);
+int pthread_join(pthread_t thread, void **retval) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_key_create.h b/libc/src/pthread/pthread_key_create.h
--- a/libc/src/pthread/pthread_key_create.h
+++ b/libc/src/pthread/pthread_key_create.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_key_create(pthread_key_t *key, __pthread_tss_dtor_t dtor);
+int pthread_key_create(pthread_key_t *key, __pthread_tss_dtor_t dtor) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_key_delete.h b/libc/src/pthread/pthread_key_delete.h
--- a/libc/src/pthread/pthread_key_delete.h
+++ b/libc/src/pthread/pthread_key_delete.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_key_delete(pthread_key_t key);
+int pthread_key_delete(pthread_key_t key) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_mutex_destroy.h b/libc/src/pthread/pthread_mutex_destroy.h
--- a/libc/src/pthread/pthread_mutex_destroy.h
+++ b/libc/src/pthread/pthread_mutex_destroy.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_mutex_destroy(pthread_mutex_t *mutex);
+int pthread_mutex_destroy(pthread_mutex_t *mutex) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_mutex_init.h b/libc/src/pthread/pthread_mutex_init.h
--- a/libc/src/pthread/pthread_mutex_init.h
+++ b/libc/src/pthread/pthread_mutex_init.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int pthread_mutex_init(pthread_mutex_t *mutex,
-                       const pthread_mutexattr_t *__restrict attr);
+                       const pthread_mutexattr_t *__restrict attr) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_mutex_lock.h b/libc/src/pthread/pthread_mutex_lock.h
--- a/libc/src/pthread/pthread_mutex_lock.h
+++ b/libc/src/pthread/pthread_mutex_lock.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_mutex_lock(pthread_mutex_t *mutex);
+int pthread_mutex_lock(pthread_mutex_t *mutex) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_mutex_unlock.h b/libc/src/pthread/pthread_mutex_unlock.h
--- a/libc/src/pthread/pthread_mutex_unlock.h
+++ b/libc/src/pthread/pthread_mutex_unlock.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_mutex_unlock(pthread_mutex_t *mutex);
+int pthread_mutex_unlock(pthread_mutex_t *mutex) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_mutexattr_destroy.h b/libc/src/pthread/pthread_mutexattr_destroy.h
--- a/libc/src/pthread/pthread_mutexattr_destroy.h
+++ b/libc/src/pthread/pthread_mutexattr_destroy.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_mutexattr_destroy(pthread_mutexattr_t *attr);
+int pthread_mutexattr_destroy(pthread_mutexattr_t *attr) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_mutexattr_getpshared.h b/libc/src/pthread/pthread_mutexattr_getpshared.h
--- a/libc/src/pthread/pthread_mutexattr_getpshared.h
+++ b/libc/src/pthread/pthread_mutexattr_getpshared.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int pthread_mutexattr_getpshared(const pthread_mutexattr_t *__restrict attr,
-                                 int *__restrict pshared);
+                                 int *__restrict pshared) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_mutexattr_getrobust.h b/libc/src/pthread/pthread_mutexattr_getrobust.h
--- a/libc/src/pthread/pthread_mutexattr_getrobust.h
+++ b/libc/src/pthread/pthread_mutexattr_getrobust.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int pthread_mutexattr_getrobust(const pthread_mutexattr_t *__restrict attr,
-                                int *__restrict robust);
+                                int *__restrict robust) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_mutexattr_gettype.h b/libc/src/pthread/pthread_mutexattr_gettype.h
--- a/libc/src/pthread/pthread_mutexattr_gettype.h
+++ b/libc/src/pthread/pthread_mutexattr_gettype.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int pthread_mutexattr_gettype(const pthread_mutexattr_t *__restrict attr,
-                              int *__restrict type);
+                              int *__restrict type) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_mutexattr_init.h b/libc/src/pthread/pthread_mutexattr_init.h
--- a/libc/src/pthread/pthread_mutexattr_init.h
+++ b/libc/src/pthread/pthread_mutexattr_init.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_mutexattr_init(pthread_mutexattr_t *attr);
+int pthread_mutexattr_init(pthread_mutexattr_t *attr) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_mutexattr_setpshared.h b/libc/src/pthread/pthread_mutexattr_setpshared.h
--- a/libc/src/pthread/pthread_mutexattr_setpshared.h
+++ b/libc/src/pthread/pthread_mutexattr_setpshared.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int pthread_mutexattr_setpshared(pthread_mutexattr_t *__restrict attr,
-                                 int pshared);
+                                 int pshared) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_mutexattr_setrobust.h b/libc/src/pthread/pthread_mutexattr_setrobust.h
--- a/libc/src/pthread/pthread_mutexattr_setrobust.h
+++ b/libc/src/pthread/pthread_mutexattr_setrobust.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int pthread_mutexattr_setrobust(pthread_mutexattr_t *__restrict attr,
-                                int robust);
+                                int robust) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_mutexattr_settype.h b/libc/src/pthread/pthread_mutexattr_settype.h
--- a/libc/src/pthread/pthread_mutexattr_settype.h
+++ b/libc/src/pthread/pthread_mutexattr_settype.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-int pthread_mutexattr_settype(pthread_mutexattr_t *__restrict attr, int type);
+int pthread_mutexattr_settype(pthread_mutexattr_t *__restrict attr,
+                              int type) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_once.h b/libc/src/pthread/pthread_once.h
--- a/libc/src/pthread/pthread_once.h
+++ b/libc/src/pthread/pthread_once.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_once(pthread_once_t *flag, __pthread_once_func_t func);
+int pthread_once(pthread_once_t *flag, __pthread_once_func_t func) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_self.h b/libc/src/pthread/pthread_self.h
--- a/libc/src/pthread/pthread_self.h
+++ b/libc/src/pthread/pthread_self.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-pthread_t pthread_self();
+pthread_t pthread_self() noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_setname_np.h b/libc/src/pthread/pthread_setname_np.h
--- a/libc/src/pthread/pthread_setname_np.h
+++ b/libc/src/pthread/pthread_setname_np.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_setname_np(pthread_t, const char *name);
+int pthread_setname_np(pthread_t, const char *name) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/pthread/pthread_setspecific.h b/libc/src/pthread/pthread_setspecific.h
--- a/libc/src/pthread/pthread_setspecific.h
+++ b/libc/src/pthread/pthread_setspecific.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int pthread_setspecific(pthread_key_t, const void *);
+int pthread_setspecific(pthread_key_t, const void *) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sched/sched_getaffinity.h b/libc/src/sched/sched_getaffinity.h
--- a/libc/src/sched/sched_getaffinity.h
+++ b/libc/src/sched/sched_getaffinity.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int sched_getaffinity(pid_t tid, size_t cpuset_size, cpu_set_t *mask);
+int sched_getaffinity(pid_t tid, size_t cpuset_size, cpu_set_t *mask) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sched/sched_getcpucount.h b/libc/src/sched/sched_getcpucount.h
--- a/libc/src/sched/sched_getcpucount.h
+++ b/libc/src/sched/sched_getcpucount.h
@@ -16,7 +16,7 @@
 
 // This function is for internal use in the CPU_COUNT macro, but since that's a
 // macro and will be applied to client files, this must be a public entrypoint.
-int __sched_getcpucount(size_t cpuset_size, const cpu_set_t *mask);
+int __sched_getcpucount(size_t cpuset_size, const cpu_set_t *mask) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sched/sched_setaffinity.h b/libc/src/sched/sched_setaffinity.h
--- a/libc/src/sched/sched_setaffinity.h
+++ b/libc/src/sched/sched_setaffinity.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-int sched_setaffinity(pid_t pid, size_t cpuset_size, const cpu_set_t *mask);
+int sched_setaffinity(pid_t pid, size_t cpuset_size,
+                      const cpu_set_t *mask) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/setjmp/longjmp.h b/libc/src/setjmp/longjmp.h
--- a/libc/src/setjmp/longjmp.h
+++ b/libc/src/setjmp/longjmp.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void longjmp(__jmp_buf *buf, int val);
+void longjmp(__jmp_buf *buf, int val) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/setjmp/setjmp_impl.h b/libc/src/setjmp/setjmp_impl.h
--- a/libc/src/setjmp/setjmp_impl.h
+++ b/libc/src/setjmp/setjmp_impl.h
@@ -15,7 +15,7 @@
 
 namespace __llvm_libc {
 
-int setjmp(__jmp_buf *buf);
+int setjmp(__jmp_buf *buf) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/signal/kill.h b/libc/src/signal/kill.h
--- a/libc/src/signal/kill.h
+++ b/libc/src/signal/kill.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int kill(pid_t pid, int sig);
+int kill(pid_t pid, int sig) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/signal/raise.h b/libc/src/signal/raise.h
--- a/libc/src/signal/raise.h
+++ b/libc/src/signal/raise.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int raise(int sig);
+int raise(int sig) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/signal/sigaction.h b/libc/src/signal/sigaction.h
--- a/libc/src/signal/sigaction.h
+++ b/libc/src/signal/sigaction.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int sigaction(int signal, const struct sigaction *__restrict libc_new,
-              struct sigaction *__restrict libc_old);
+              struct sigaction *__restrict libc_old) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/signal/sigaddset.h b/libc/src/signal/sigaddset.h
--- a/libc/src/signal/sigaddset.h
+++ b/libc/src/signal/sigaddset.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int sigaddset(sigset_t *set, int signum);
+int sigaddset(sigset_t *set, int signum) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/signal/sigaltstack.h b/libc/src/signal/sigaltstack.h
--- a/libc/src/signal/sigaltstack.h
+++ b/libc/src/signal/sigaltstack.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int sigaltstack(const stack_t *__restrict ss, stack_t *__restrict oss);
+int sigaltstack(const stack_t *__restrict ss, stack_t *__restrict oss) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/signal/sigdelset.h b/libc/src/signal/sigdelset.h
--- a/libc/src/signal/sigdelset.h
+++ b/libc/src/signal/sigdelset.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int sigdelset(sigset_t *set, int signum);
+int sigdelset(sigset_t *set, int signum) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/signal/sigemptyset.h b/libc/src/signal/sigemptyset.h
--- a/libc/src/signal/sigemptyset.h
+++ b/libc/src/signal/sigemptyset.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int sigemptyset(sigset_t *set);
+int sigemptyset(sigset_t *set) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/signal/sigfillset.h b/libc/src/signal/sigfillset.h
--- a/libc/src/signal/sigfillset.h
+++ b/libc/src/signal/sigfillset.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int sigfillset(sigset_t *set);
+int sigfillset(sigset_t *set) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/signal/signal.h b/libc/src/signal/signal.h
--- a/libc/src/signal/signal.h
+++ b/libc/src/signal/signal.h
@@ -15,7 +15,7 @@
 
 using sighandler_t = __sighandler_t;
 
-sighandler_t signal(int signum, sighandler_t handler);
+sighandler_t signal(int signum, sighandler_t handler) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/signal/sigprocmask.h b/libc/src/signal/sigprocmask.h
--- a/libc/src/signal/sigprocmask.h
+++ b/libc/src/signal/sigprocmask.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int sigprocmask(int how, const sigset_t *__restrict set,
-                sigset_t *__restrict oldset);
+                sigset_t *__restrict oldset) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/spawn/posix_spawn.h b/libc/src/spawn/posix_spawn.h
--- a/libc/src/spawn/posix_spawn.h
+++ b/libc/src/spawn/posix_spawn.h
@@ -16,7 +16,8 @@
 int posix_spawn(pid_t *__restrict pid, const char *__restrict path,
                 const posix_spawn_file_actions_t *file_actions,
                 const posix_spawnattr_t *__restrict attr,
-                char *const *__restrict argv, char *const *__restrict envp);
+                char *const *__restrict argv,
+                char *const *__restrict envp) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/spawn/posix_spawn_file_actions_addclose.h b/libc/src/spawn/posix_spawn_file_actions_addclose.h
--- a/libc/src/spawn/posix_spawn_file_actions_addclose.h
+++ b/libc/src/spawn/posix_spawn_file_actions_addclose.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int posix_spawn_file_actions_addclose(
-    posix_spawn_file_actions_t *__restrict actions, int fd);
+    posix_spawn_file_actions_t *__restrict actions, int fd) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/spawn/posix_spawn_file_actions_adddup2.h b/libc/src/spawn/posix_spawn_file_actions_adddup2.h
--- a/libc/src/spawn/posix_spawn_file_actions_adddup2.h
+++ b/libc/src/spawn/posix_spawn_file_actions_adddup2.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int posix_spawn_file_actions_adddup2(posix_spawn_file_actions_t *actions,
-                                     int fd, int newfd);
+                                     int fd, int newfd) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/spawn/posix_spawn_file_actions_addopen.h b/libc/src/spawn/posix_spawn_file_actions_addopen.h
--- a/libc/src/spawn/posix_spawn_file_actions_addopen.h
+++ b/libc/src/spawn/posix_spawn_file_actions_addopen.h
@@ -15,7 +15,7 @@
 
 int posix_spawn_file_actions_addopen(
     posix_spawn_file_actions_t *__restrict actions, int fd,
-    const char *__restrict path, int oflag, mode_t mode);
+    const char *__restrict path, int oflag, mode_t mode) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/spawn/posix_spawn_file_actions_destroy.h b/libc/src/spawn/posix_spawn_file_actions_destroy.h
--- a/libc/src/spawn/posix_spawn_file_actions_destroy.h
+++ b/libc/src/spawn/posix_spawn_file_actions_destroy.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-int posix_spawn_file_actions_destroy(posix_spawn_file_actions_t *actions);
+int posix_spawn_file_actions_destroy(
+    posix_spawn_file_actions_t *actions) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/spawn/posix_spawn_file_actions_init.h b/libc/src/spawn/posix_spawn_file_actions_init.h
--- a/libc/src/spawn/posix_spawn_file_actions_init.h
+++ b/libc/src/spawn/posix_spawn_file_actions_init.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int posix_spawn_file_actions_init(posix_spawn_file_actions_t *actions);
+int posix_spawn_file_actions_init(posix_spawn_file_actions_t *actions) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/clearerr.h b/libc/src/stdio/clearerr.h
--- a/libc/src/stdio/clearerr.h
+++ b/libc/src/stdio/clearerr.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void clearerr(::FILE *stream);
+void clearerr(::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/clearerr_unlocked.h b/libc/src/stdio/clearerr_unlocked.h
--- a/libc/src/stdio/clearerr_unlocked.h
+++ b/libc/src/stdio/clearerr_unlocked.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void clearerr_unlocked(::FILE *stream);
+void clearerr_unlocked(::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fclose.h b/libc/src/stdio/fclose.h
--- a/libc/src/stdio/fclose.h
+++ b/libc/src/stdio/fclose.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fclose(::FILE *stream);
+int fclose(::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/feof.h b/libc/src/stdio/feof.h
--- a/libc/src/stdio/feof.h
+++ b/libc/src/stdio/feof.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int feof(::FILE *stream);
+int feof(::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/feof_unlocked.h b/libc/src/stdio/feof_unlocked.h
--- a/libc/src/stdio/feof_unlocked.h
+++ b/libc/src/stdio/feof_unlocked.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int feof_unlocked(::FILE *stream);
+int feof_unlocked(::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/ferror.h b/libc/src/stdio/ferror.h
--- a/libc/src/stdio/ferror.h
+++ b/libc/src/stdio/ferror.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int ferror(::FILE *stream);
+int ferror(::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/ferror_unlocked.h b/libc/src/stdio/ferror_unlocked.h
--- a/libc/src/stdio/ferror_unlocked.h
+++ b/libc/src/stdio/ferror_unlocked.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int ferror_unlocked(::FILE *stream);
+int ferror_unlocked(::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fflush.h b/libc/src/stdio/fflush.h
--- a/libc/src/stdio/fflush.h
+++ b/libc/src/stdio/fflush.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fflush(::FILE *stream);
+int fflush(::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fgetc.h b/libc/src/stdio/fgetc.h
--- a/libc/src/stdio/fgetc.h
+++ b/libc/src/stdio/fgetc.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fgetc(::FILE *f);
+int fgetc(::FILE *f) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fgetc_unlocked.h b/libc/src/stdio/fgetc_unlocked.h
--- a/libc/src/stdio/fgetc_unlocked.h
+++ b/libc/src/stdio/fgetc_unlocked.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fgetc_unlocked(::FILE *f);
+int fgetc_unlocked(::FILE *f) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fgets.h b/libc/src/stdio/fgets.h
--- a/libc/src/stdio/fgets.h
+++ b/libc/src/stdio/fgets.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-char *fgets(char *__restrict str, int count, ::FILE *__restrict raw_stream);
+char *fgets(char *__restrict str, int count,
+            ::FILE *__restrict raw_stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/flockfile.h b/libc/src/stdio/flockfile.h
--- a/libc/src/stdio/flockfile.h
+++ b/libc/src/stdio/flockfile.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void flockfile(::FILE *stream);
+void flockfile(::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fopen.h b/libc/src/stdio/fopen.h
--- a/libc/src/stdio/fopen.h
+++ b/libc/src/stdio/fopen.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-::FILE *fopen(const char *__restrict name, const char *__restrict mode);
+::FILE *fopen(const char *__restrict name,
+              const char *__restrict mode) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fopencookie.h b/libc/src/stdio/fopencookie.h
--- a/libc/src/stdio/fopencookie.h
+++ b/libc/src/stdio/fopencookie.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 ::FILE *fopencookie(void *cookie, const char *__restrict mode,
-                    cookie_io_functions_t desc);
+                    cookie_io_functions_t desc) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fprintf.h b/libc/src/stdio/fprintf.h
--- a/libc/src/stdio/fprintf.h
+++ b/libc/src/stdio/fprintf.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-int fprintf(::FILE *__restrict stream, const char *__restrict format, ...);
+int fprintf(::FILE *__restrict stream, const char *__restrict format,
+            ...) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fputc.h b/libc/src/stdio/fputc.h
--- a/libc/src/stdio/fputc.h
+++ b/libc/src/stdio/fputc.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fputc(int c, ::FILE *stream);
+int fputc(int c, ::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fputs.h b/libc/src/stdio/fputs.h
--- a/libc/src/stdio/fputs.h
+++ b/libc/src/stdio/fputs.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fputs(const char *__restrict str, ::FILE *__restrict stream);
+int fputs(const char *__restrict str, ::FILE *__restrict stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fread.h b/libc/src/stdio/fread.h
--- a/libc/src/stdio/fread.h
+++ b/libc/src/stdio/fread.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 size_t fread(void *__restrict buffer, size_t size, size_t nmemb,
-             ::FILE *stream);
+             ::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fread_unlocked.h b/libc/src/stdio/fread_unlocked.h
--- a/libc/src/stdio/fread_unlocked.h
+++ b/libc/src/stdio/fread_unlocked.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 size_t fread_unlocked(void *__restrict buffer, size_t size, size_t nmemb,
-                      ::FILE *stream);
+                      ::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fscanf.h b/libc/src/stdio/fscanf.h
--- a/libc/src/stdio/fscanf.h
+++ b/libc/src/stdio/fscanf.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-int fscanf(::FILE *__restrict stream, const char *__restrict format, ...);
+int fscanf(::FILE *__restrict stream, const char *__restrict format,
+           ...) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fseek.h b/libc/src/stdio/fseek.h
--- a/libc/src/stdio/fseek.h
+++ b/libc/src/stdio/fseek.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fseek(::FILE *stream, long offset, int whence);
+int fseek(::FILE *stream, long offset, int whence) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/ftell.h b/libc/src/stdio/ftell.h
--- a/libc/src/stdio/ftell.h
+++ b/libc/src/stdio/ftell.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-long ftell(::FILE *f);
+long ftell(::FILE *f) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/funlockfile.h b/libc/src/stdio/funlockfile.h
--- a/libc/src/stdio/funlockfile.h
+++ b/libc/src/stdio/funlockfile.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void funlockfile(::FILE *stream);
+void funlockfile(::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fwrite.h b/libc/src/stdio/fwrite.h
--- a/libc/src/stdio/fwrite.h
+++ b/libc/src/stdio/fwrite.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 size_t fwrite(const void *__restrict ptr, size_t size, size_t nmemb,
-              ::FILE *__restrict stream);
+              ::FILE *__restrict stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/fwrite_unlocked.h b/libc/src/stdio/fwrite_unlocked.h
--- a/libc/src/stdio/fwrite_unlocked.h
+++ b/libc/src/stdio/fwrite_unlocked.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 size_t fwrite_unlocked(const void *__restrict ptr, size_t size, size_t nmemb,
-                       ::FILE *__restrict stream);
+                       ::FILE *__restrict stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/getc.h b/libc/src/stdio/getc.h
--- a/libc/src/stdio/getc.h
+++ b/libc/src/stdio/getc.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int getc(::FILE *f);
+int getc(::FILE *f) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/getc_unlocked.h b/libc/src/stdio/getc_unlocked.h
--- a/libc/src/stdio/getc_unlocked.h
+++ b/libc/src/stdio/getc_unlocked.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int getc_unlocked(::FILE *f);
+int getc_unlocked(::FILE *f) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/printf.h b/libc/src/stdio/printf.h
--- a/libc/src/stdio/printf.h
+++ b/libc/src/stdio/printf.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int printf(const char *__restrict format, ...);
+int printf(const char *__restrict format, ...) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/putc.h b/libc/src/stdio/putc.h
--- a/libc/src/stdio/putc.h
+++ b/libc/src/stdio/putc.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int putc(int c, ::FILE *stream);
+int putc(int c, ::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/putchar.h b/libc/src/stdio/putchar.h
--- a/libc/src/stdio/putchar.h
+++ b/libc/src/stdio/putchar.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int putchar(int c);
+int putchar(int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/puts.h b/libc/src/stdio/puts.h
--- a/libc/src/stdio/puts.h
+++ b/libc/src/stdio/puts.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int puts(const char *__restrict str);
+int puts(const char *__restrict str) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/remove.h b/libc/src/stdio/remove.h
--- a/libc/src/stdio/remove.h
+++ b/libc/src/stdio/remove.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int remove(const char *path);
+int remove(const char *path) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/scanf.h b/libc/src/stdio/scanf.h
--- a/libc/src/stdio/scanf.h
+++ b/libc/src/stdio/scanf.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int scanf(const char *__restrict format, ...);
+int scanf(const char *__restrict format, ...) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/setbuf.h b/libc/src/stdio/setbuf.h
--- a/libc/src/stdio/setbuf.h
+++ b/libc/src/stdio/setbuf.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void setbuf(::FILE *__restrict stream, char *__restrict buf);
+void setbuf(::FILE *__restrict stream, char *__restrict buf) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/setvbuf.h b/libc/src/stdio/setvbuf.h
--- a/libc/src/stdio/setvbuf.h
+++ b/libc/src/stdio/setvbuf.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int setvbuf(::FILE *__restrict stream, char *__restrict buf, int type,
-            size_t size);
+            size_t size) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/snprintf.h b/libc/src/stdio/snprintf.h
--- a/libc/src/stdio/snprintf.h
+++ b/libc/src/stdio/snprintf.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 int snprintf(char *__restrict buffer, size_t buffsz,
-             const char *__restrict format, ...);
+             const char *__restrict format, ...) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/sprintf.h b/libc/src/stdio/sprintf.h
--- a/libc/src/stdio/sprintf.h
+++ b/libc/src/stdio/sprintf.h
@@ -11,7 +11,8 @@
 
 namespace __llvm_libc {
 
-int sprintf(char *__restrict buffer, const char *__restrict format, ...);
+int sprintf(char *__restrict buffer, const char *__restrict format,
+            ...) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/sscanf.h b/libc/src/stdio/sscanf.h
--- a/libc/src/stdio/sscanf.h
+++ b/libc/src/stdio/sscanf.h
@@ -11,7 +11,8 @@
 
 namespace __llvm_libc {
 
-int sscanf(const char *__restrict buffer, const char *__restrict format, ...);
+int sscanf(const char *__restrict buffer, const char *__restrict format,
+           ...) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdio/ungetc.h b/libc/src/stdio/ungetc.h
--- a/libc/src/stdio/ungetc.h
+++ b/libc/src/stdio/ungetc.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int ungetc(int c, ::FILE *stream);
+int ungetc(int c, ::FILE *stream) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/_Exit.h b/libc/src/stdlib/_Exit.h
--- a/libc/src/stdlib/_Exit.h
+++ b/libc/src/stdlib/_Exit.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-[[noreturn]] void _Exit(int status);
+[[noreturn]] void _Exit(int status) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/abort.h b/libc/src/stdlib/abort.h
--- a/libc/src/stdlib/abort.h
+++ b/libc/src/stdlib/abort.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-[[noreturn]] void abort();
+[[noreturn]] void abort() noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/abs.h b/libc/src/stdlib/abs.h
--- a/libc/src/stdlib/abs.h
+++ b/libc/src/stdlib/abs.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int abs(int n);
+int abs(int n) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/atexit.h b/libc/src/stdlib/atexit.h
--- a/libc/src/stdlib/atexit.h
+++ b/libc/src/stdlib/atexit.h
@@ -15,7 +15,7 @@
 
 constexpr size_t CALLBACK_LIST_SIZE_FOR_TESTS = 1024;
 
-int atexit(void (*function)());
+int atexit(void (*function)()) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/atof.h b/libc/src/stdlib/atof.h
--- a/libc/src/stdlib/atof.h
+++ b/libc/src/stdlib/atof.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double atof(const char *str);
+double atof(const char *str) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/atoi.h b/libc/src/stdlib/atoi.h
--- a/libc/src/stdlib/atoi.h
+++ b/libc/src/stdlib/atoi.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int atoi(const char *str);
+int atoi(const char *str) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/atol.h b/libc/src/stdlib/atol.h
--- a/libc/src/stdlib/atol.h
+++ b/libc/src/stdlib/atol.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long atol(const char *str);
+long atol(const char *str) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/atoll.h b/libc/src/stdlib/atoll.h
--- a/libc/src/stdlib/atoll.h
+++ b/libc/src/stdlib/atoll.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long long atoll(const char *str);
+long long atoll(const char *str) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/bsearch.h b/libc/src/stdlib/bsearch.h
--- a/libc/src/stdlib/bsearch.h
+++ b/libc/src/stdlib/bsearch.h
@@ -11,6 +11,7 @@
 namespace __llvm_libc {
 
 void *bsearch(const void *key, const void *array, size_t array_size,
-              size_t elem_size, int (*compare)(const void *, const void *));
+              size_t elem_size,
+              int (*compare)(const void *, const void *)) noexcept;
 
 } // namespace __llvm_libc
diff --git a/libc/src/stdlib/div.h b/libc/src/stdlib/div.h
--- a/libc/src/stdlib/div.h
+++ b/libc/src/stdlib/div.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-div_t div(int x, int y);
+div_t div(int x, int y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/exit.h b/libc/src/stdlib/exit.h
--- a/libc/src/stdlib/exit.h
+++ b/libc/src/stdlib/exit.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void exit(int status);
+void exit(int status) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/getenv.h b/libc/src/stdlib/getenv.h
--- a/libc/src/stdlib/getenv.h
+++ b/libc/src/stdlib/getenv.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-char *getenv(const char *name);
+char *getenv(const char *name) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/labs.h b/libc/src/stdlib/labs.h
--- a/libc/src/stdlib/labs.h
+++ b/libc/src/stdlib/labs.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long labs(long n);
+long labs(long n) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/ldiv.h b/libc/src/stdlib/ldiv.h
--- a/libc/src/stdlib/ldiv.h
+++ b/libc/src/stdlib/ldiv.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-ldiv_t ldiv(long x, long y);
+ldiv_t ldiv(long x, long y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/llabs.h b/libc/src/stdlib/llabs.h
--- a/libc/src/stdlib/llabs.h
+++ b/libc/src/stdlib/llabs.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-long long llabs(long long n);
+long long llabs(long long n) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/lldiv.h b/libc/src/stdlib/lldiv.h
--- a/libc/src/stdlib/lldiv.h
+++ b/libc/src/stdlib/lldiv.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-lldiv_t lldiv(long long x, long long y);
+lldiv_t lldiv(long long x, long long y) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/qsort.h b/libc/src/stdlib/qsort.h
--- a/libc/src/stdlib/qsort.h
+++ b/libc/src/stdlib/qsort.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 void qsort(void *array, size_t array_size, size_t elem_size,
-           int (*compare)(const void *, const void *));
+           int (*compare)(const void *, const void *)) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/rand.h b/libc/src/stdlib/rand.h
--- a/libc/src/stdlib/rand.h
+++ b/libc/src/stdlib/rand.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int rand(void);
+int rand(void) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/srand.h b/libc/src/stdlib/srand.h
--- a/libc/src/stdlib/srand.h
+++ b/libc/src/stdlib/srand.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void srand(unsigned int seed);
+void srand(unsigned int seed) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/strtod.h b/libc/src/stdlib/strtod.h
--- a/libc/src/stdlib/strtod.h
+++ b/libc/src/stdlib/strtod.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-double strtod(const char *__restrict str, char **__restrict str_end);
+double strtod(const char *__restrict str, char **__restrict str_end) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/strtof.h b/libc/src/stdlib/strtof.h
--- a/libc/src/stdlib/strtof.h
+++ b/libc/src/stdlib/strtof.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-float strtof(const char *__restrict str, char **__restrict str_end);
+float strtof(const char *__restrict str, char **__restrict str_end) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/strtol.h b/libc/src/stdlib/strtol.h
--- a/libc/src/stdlib/strtol.h
+++ b/libc/src/stdlib/strtol.h
@@ -11,7 +11,8 @@
 
 namespace __llvm_libc {
 
-long strtol(const char *__restrict str, char **__restrict str_end, int base);
+long strtol(const char *__restrict str, char **__restrict str_end,
+            int base) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/strtold.h b/libc/src/stdlib/strtold.h
--- a/libc/src/stdlib/strtold.h
+++ b/libc/src/stdlib/strtold.h
@@ -11,7 +11,8 @@
 
 namespace __llvm_libc {
 
-long double strtold(const char *__restrict str, char **__restrict str_end);
+long double strtold(const char *__restrict str,
+                    char **__restrict str_end) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/strtoll.h b/libc/src/stdlib/strtoll.h
--- a/libc/src/stdlib/strtoll.h
+++ b/libc/src/stdlib/strtoll.h
@@ -12,7 +12,7 @@
 namespace __llvm_libc {
 
 long long strtoll(const char *__restrict str, char **__restrict str_end,
-                  int base);
+                  int base) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/strtoul.h b/libc/src/stdlib/strtoul.h
--- a/libc/src/stdlib/strtoul.h
+++ b/libc/src/stdlib/strtoul.h
@@ -12,7 +12,7 @@
 namespace __llvm_libc {
 
 unsigned long strtoul(const char *__restrict str, char **__restrict str_end,
-                      int base);
+                      int base) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/stdlib/strtoull.h b/libc/src/stdlib/strtoull.h
--- a/libc/src/stdlib/strtoull.h
+++ b/libc/src/stdlib/strtoull.h
@@ -12,7 +12,7 @@
 namespace __llvm_libc {
 
 unsigned long long strtoull(const char *__restrict str,
-                            char **__restrict str_end, int base);
+                            char **__restrict str_end, int base) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/bcmp.h b/libc/src/string/bcmp.h
--- a/libc/src/string/bcmp.h
+++ b/libc/src/string/bcmp.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int bcmp(const void *lhs, const void *rhs, size_t count);
+int bcmp(const void *lhs, const void *rhs, size_t count) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/bcopy.h b/libc/src/string/bcopy.h
--- a/libc/src/string/bcopy.h
+++ b/libc/src/string/bcopy.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void bcopy(const void *src, void *dest, size_t count);
+void bcopy(const void *src, void *dest, size_t count) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/bzero.h b/libc/src/string/bzero.h
--- a/libc/src/string/bzero.h
+++ b/libc/src/string/bzero.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void bzero(void *ptr, size_t count);
+void bzero(void *ptr, size_t count) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/memccpy.h b/libc/src/string/memccpy.h
--- a/libc/src/string/memccpy.h
+++ b/libc/src/string/memccpy.h
@@ -14,7 +14,7 @@
 namespace __llvm_libc {
 
 void *memccpy(void *__restrict dest, const void *__restrict src, int c,
-              size_t count);
+              size_t count) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/memchr.h b/libc/src/string/memchr.h
--- a/libc/src/string/memchr.h
+++ b/libc/src/string/memchr.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void *memchr(const void *src, int c, size_t n);
+void *memchr(const void *src, int c, size_t n) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/memcmp.h b/libc/src/string/memcmp.h
--- a/libc/src/string/memcmp.h
+++ b/libc/src/string/memcmp.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int memcmp(const void *lhs, const void *rhs, size_t count);
+int memcmp(const void *lhs, const void *rhs, size_t count) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/memcpy.h b/libc/src/string/memcpy.h
--- a/libc/src/string/memcpy.h
+++ b/libc/src/string/memcpy.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void *memcpy(void *__restrict, const void *__restrict, size_t);
+void *memcpy(void *__restrict, const void *__restrict, size_t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/memmove.h b/libc/src/string/memmove.h
--- a/libc/src/string/memmove.h
+++ b/libc/src/string/memmove.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void *memmove(void *dst, const void *src, size_t count);
+void *memmove(void *dst, const void *src, size_t count) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/mempcpy.h b/libc/src/string/mempcpy.h
--- a/libc/src/string/mempcpy.h
+++ b/libc/src/string/mempcpy.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-void *mempcpy(void *__restrict dest, const void *__restrict src, size_t count);
+void *mempcpy(void *__restrict dest, const void *__restrict src,
+              size_t count) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/memrchr.h b/libc/src/string/memrchr.h
--- a/libc/src/string/memrchr.h
+++ b/libc/src/string/memrchr.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void *memrchr(const void *src, int c, size_t n);
+void *memrchr(const void *src, int c, size_t n) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/memset.h b/libc/src/string/memset.h
--- a/libc/src/string/memset.h
+++ b/libc/src/string/memset.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void *memset(void *ptr, int value, size_t count);
+void *memset(void *ptr, int value, size_t count) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/stpcpy.h b/libc/src/string/stpcpy.h
--- a/libc/src/string/stpcpy.h
+++ b/libc/src/string/stpcpy.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-char *stpcpy(char *__restrict dest, const char *__restrict src);
+char *stpcpy(char *__restrict dest, const char *__restrict src) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/stpncpy.h b/libc/src/string/stpncpy.h
--- a/libc/src/string/stpncpy.h
+++ b/libc/src/string/stpncpy.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-char *stpncpy(char *__restrict dest, const char *__restrict src, size_t n);
+char *stpncpy(char *__restrict dest, const char *__restrict src,
+              size_t n) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strcat.h b/libc/src/string/strcat.h
--- a/libc/src/string/strcat.h
+++ b/libc/src/string/strcat.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-char *strcat(char *__restrict dest, const char *__restrict src);
+char *strcat(char *__restrict dest, const char *__restrict src) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strchr.h b/libc/src/string/strchr.h
--- a/libc/src/string/strchr.h
+++ b/libc/src/string/strchr.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-char *strchr(const char *src, int c);
+char *strchr(const char *src, int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strcmp.h b/libc/src/string/strcmp.h
--- a/libc/src/string/strcmp.h
+++ b/libc/src/string/strcmp.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int strcmp(const char *left, const char *right);
+int strcmp(const char *left, const char *right) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strcoll.h b/libc/src/string/strcoll.h
--- a/libc/src/string/strcoll.h
+++ b/libc/src/string/strcoll.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int strcoll(const char *left, const char *right);
+int strcoll(const char *left, const char *right) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strcpy.h b/libc/src/string/strcpy.h
--- a/libc/src/string/strcpy.h
+++ b/libc/src/string/strcpy.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-char *strcpy(char *__restrict dest, const char *__restrict src);
+char *strcpy(char *__restrict dest, const char *__restrict src) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strcspn.h b/libc/src/string/strcspn.h
--- a/libc/src/string/strcspn.h
+++ b/libc/src/string/strcspn.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-size_t strcspn(const char *src, const char *segment);
+size_t strcspn(const char *src, const char *segment) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strdup.h b/libc/src/string/strdup.h
--- a/libc/src/string/strdup.h
+++ b/libc/src/string/strdup.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-char *strdup(const char *src);
+char *strdup(const char *src) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strerror.h b/libc/src/string/strerror.h
--- a/libc/src/string/strerror.h
+++ b/libc/src/string/strerror.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-char *strerror(int err_num);
+char *strerror(int err_num) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strerror_r.h b/libc/src/string/strerror_r.h
--- a/libc/src/string/strerror_r.h
+++ b/libc/src/string/strerror_r.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-char *strerror_r(int err_num, char *buf, size_t buflen);
+char *strerror_r(int err_num, char *buf, size_t buflen) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strlcat.h b/libc/src/string/strlcat.h
--- a/libc/src/string/strlcat.h
+++ b/libc/src/string/strlcat.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-size_t strlcat(char *__restrict dst, const char *__restrict src, size_t size);
+size_t strlcat(char *__restrict dst, const char *__restrict src,
+               size_t size) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strlcpy.h b/libc/src/string/strlcpy.h
--- a/libc/src/string/strlcpy.h
+++ b/libc/src/string/strlcpy.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-size_t strlcpy(char *__restrict dst, const char *__restrict src, size_t size);
+size_t strlcpy(char *__restrict dst, const char *__restrict src,
+               size_t size) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strlen.h b/libc/src/string/strlen.h
--- a/libc/src/string/strlen.h
+++ b/libc/src/string/strlen.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-size_t strlen(const char *src);
+size_t strlen(const char *src) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strncat.h b/libc/src/string/strncat.h
--- a/libc/src/string/strncat.h
+++ b/libc/src/string/strncat.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-char *strncat(char *__restrict dest, const char *__restrict src, size_t count);
+char *strncat(char *__restrict dest, const char *__restrict src,
+              size_t count) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strncmp.h b/libc/src/string/strncmp.h
--- a/libc/src/string/strncmp.h
+++ b/libc/src/string/strncmp.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int strncmp(const char *left, const char *right, size_t n);
+int strncmp(const char *left, const char *right, size_t n) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strncpy.h b/libc/src/string/strncpy.h
--- a/libc/src/string/strncpy.h
+++ b/libc/src/string/strncpy.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-char *strncpy(char *__restrict dest, const char *__restrict src, size_t n);
+char *strncpy(char *__restrict dest, const char *__restrict src,
+              size_t n) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strndup.h b/libc/src/string/strndup.h
--- a/libc/src/string/strndup.h
+++ b/libc/src/string/strndup.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-char *strndup(const char *src, size_t size);
+char *strndup(const char *src, size_t size) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strnlen.h b/libc/src/string/strnlen.h
--- a/libc/src/string/strnlen.h
+++ b/libc/src/string/strnlen.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-size_t strnlen(const char *src, size_t n);
+size_t strnlen(const char *src, size_t n) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strpbrk.h b/libc/src/string/strpbrk.h
--- a/libc/src/string/strpbrk.h
+++ b/libc/src/string/strpbrk.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-char *strpbrk(const char *src, const char *breakset);
+char *strpbrk(const char *src, const char *breakset) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strrchr.h b/libc/src/string/strrchr.h
--- a/libc/src/string/strrchr.h
+++ b/libc/src/string/strrchr.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-char *strrchr(const char *src, int c);
+char *strrchr(const char *src, int c) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strsignal.h b/libc/src/string/strsignal.h
--- a/libc/src/string/strsignal.h
+++ b/libc/src/string/strsignal.h
@@ -12,7 +12,7 @@
 
 namespace __llvm_libc {
 
-char *strsignal(int sig_num);
+char *strsignal(int sig_num) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strspn.h b/libc/src/string/strspn.h
--- a/libc/src/string/strspn.h
+++ b/libc/src/string/strspn.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-size_t strspn(const char *src, const char *segment);
+size_t strspn(const char *src, const char *segment) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strstr.h b/libc/src/string/strstr.h
--- a/libc/src/string/strstr.h
+++ b/libc/src/string/strstr.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-char *strstr(const char *haystack, const char *needle);
+char *strstr(const char *haystack, const char *needle) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strtok.h b/libc/src/string/strtok.h
--- a/libc/src/string/strtok.h
+++ b/libc/src/string/strtok.h
@@ -11,7 +11,8 @@
 
 namespace __llvm_libc {
 
-char *strtok(char *__restrict src, const char *__restrict delimiter_string);
+char *strtok(char *__restrict src,
+             const char *__restrict delimiter_string) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/string/strtok_r.h b/libc/src/string/strtok_r.h
--- a/libc/src/string/strtok_r.h
+++ b/libc/src/string/strtok_r.h
@@ -12,7 +12,7 @@
 namespace __llvm_libc {
 
 char *strtok_r(char *__restrict src, const char *__restrict delimiter_string,
-               char **__restrict saveptr);
+               char **__restrict saveptr) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/mman/madvise.h b/libc/src/sys/mman/madvise.h
--- a/libc/src/sys/mman/madvise.h
+++ b/libc/src/sys/mman/madvise.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int madvise(void *addr, size_t size, int advice);
+int madvise(void *addr, size_t size, int advice) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/mman/mmap.h b/libc/src/sys/mman/mmap.h
--- a/libc/src/sys/mman/mmap.h
+++ b/libc/src/sys/mman/mmap.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-void *mmap(void *addr, size_t size, int prot, int flags, int fd, off_t offset);
+void *mmap(void *addr, size_t size, int prot, int flags, int fd,
+           off_t offset) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/mman/mprotect.h b/libc/src/sys/mman/mprotect.h
--- a/libc/src/sys/mman/mprotect.h
+++ b/libc/src/sys/mman/mprotect.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int mprotect(void *addr, size_t size, int prot);
+int mprotect(void *addr, size_t size, int prot) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/mman/munmap.h b/libc/src/sys/mman/munmap.h
--- a/libc/src/sys/mman/munmap.h
+++ b/libc/src/sys/mman/munmap.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int munmap(void *addr, size_t size);
+int munmap(void *addr, size_t size) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/mman/posix_madvise.h b/libc/src/sys/mman/posix_madvise.h
--- a/libc/src/sys/mman/posix_madvise.h
+++ b/libc/src/sys/mman/posix_madvise.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int posix_madvise(void *addr, size_t size, int advice);
+int posix_madvise(void *addr, size_t size, int advice) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/random/getrandom.h b/libc/src/sys/random/getrandom.h
--- a/libc/src/sys/random/getrandom.h
+++ b/libc/src/sys/random/getrandom.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-ssize_t getrandom(void *buf, size_t buflen, unsigned int flags);
+ssize_t getrandom(void *buf, size_t buflen, unsigned int flags) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/resource/getrlimit.h b/libc/src/sys/resource/getrlimit.h
--- a/libc/src/sys/resource/getrlimit.h
+++ b/libc/src/sys/resource/getrlimit.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int getrlimit(int resource, struct rlimit *lim);
+int getrlimit(int resource, struct rlimit *lim) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/resource/setrlimit.h b/libc/src/sys/resource/setrlimit.h
--- a/libc/src/sys/resource/setrlimit.h
+++ b/libc/src/sys/resource/setrlimit.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int setrlimit(int resource, const struct rlimit *lim);
+int setrlimit(int resource, const struct rlimit *lim) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/select/select.h b/libc/src/sys/select/select.h
--- a/libc/src/sys/select/select.h
+++ b/libc/src/sys/select/select.h
@@ -14,7 +14,8 @@
 namespace __llvm_libc {
 
 int select(int nfds, fd_set *__restrict read_set, fd_set *__restrict write_set,
-           fd_set *__restrict error_set, struct timeval *__restrict timeout);
+           fd_set *__restrict error_set,
+           struct timeval *__restrict timeout) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/sendfile/sendfile.h b/libc/src/sys/sendfile/sendfile.h
--- a/libc/src/sys/sendfile/sendfile.h
+++ b/libc/src/sys/sendfile/sendfile.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-ssize_t sendfile(int, int, off_t *, size_t);
+ssize_t sendfile(int, int, off_t *, size_t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/stat/chmod.h b/libc/src/sys/stat/chmod.h
--- a/libc/src/sys/stat/chmod.h
+++ b/libc/src/sys/stat/chmod.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int chmod(const char *path, mode_t mode);
+int chmod(const char *path, mode_t mode) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/stat/fchmod.h b/libc/src/sys/stat/fchmod.h
--- a/libc/src/sys/stat/fchmod.h
+++ b/libc/src/sys/stat/fchmod.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fchmod(int fd, mode_t mode);
+int fchmod(int fd, mode_t mode) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/stat/fchmodat.h b/libc/src/sys/stat/fchmodat.h
--- a/libc/src/sys/stat/fchmodat.h
+++ b/libc/src/sys/stat/fchmodat.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fchmodat(int dirfd, const char *path, mode_t mode, int flags);
+int fchmodat(int dirfd, const char *path, mode_t mode, int flags) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/stat/fstat.h b/libc/src/sys/stat/fstat.h
--- a/libc/src/sys/stat/fstat.h
+++ b/libc/src/sys/stat/fstat.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int fstat(int fd, struct stat *statbuf);
+int fstat(int fd, struct stat *statbuf) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/stat/lstat.h b/libc/src/sys/stat/lstat.h
--- a/libc/src/sys/stat/lstat.h
+++ b/libc/src/sys/stat/lstat.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-int lstat(const char *__restrict path, struct stat *__restrict statbuf);
+int lstat(const char *__restrict path,
+          struct stat *__restrict statbuf) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/stat/mkdir.h b/libc/src/sys/stat/mkdir.h
--- a/libc/src/sys/stat/mkdir.h
+++ b/libc/src/sys/stat/mkdir.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int mkdir(const char *path, mode_t mode);
+int mkdir(const char *path, mode_t mode) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/stat/mkdirat.h b/libc/src/sys/stat/mkdirat.h
--- a/libc/src/sys/stat/mkdirat.h
+++ b/libc/src/sys/stat/mkdirat.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int mkdirat(int dfd, const char *path, mode_t mode);
+int mkdirat(int dfd, const char *path, mode_t mode) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/stat/stat.h b/libc/src/sys/stat/stat.h
--- a/libc/src/sys/stat/stat.h
+++ b/libc/src/sys/stat/stat.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int stat(const char *__restrict path, struct stat *__restrict statbuf);
+int stat(const char *__restrict path, struct stat *__restrict statbuf) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/utsname/uname.h b/libc/src/sys/utsname/uname.h
--- a/libc/src/sys/utsname/uname.h
+++ b/libc/src/sys/utsname/uname.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int uname(struct utsname *name);
+int uname(struct utsname *name) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/wait/wait.h b/libc/src/sys/wait/wait.h
--- a/libc/src/sys/wait/wait.h
+++ b/libc/src/sys/wait/wait.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-pid_t wait(int *waitstatus);
+pid_t wait(int *waitstatus) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/wait/wait4.h b/libc/src/sys/wait/wait4.h
--- a/libc/src/sys/wait/wait4.h
+++ b/libc/src/sys/wait/wait4.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-pid_t wait4(pid_t pid, int *waitstatus, int options, struct rusage *usage);
+pid_t wait4(pid_t pid, int *waitstatus, int options,
+            struct rusage *usage) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/sys/wait/waitpid.h b/libc/src/sys/wait/waitpid.h
--- a/libc/src/sys/wait/waitpid.h
+++ b/libc/src/sys/wait/waitpid.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-pid_t waitpid(pid_t pid, int *waitstatus, int options);
+pid_t waitpid(pid_t pid, int *waitstatus, int options) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/termios/cfgetispeed.h b/libc/src/termios/cfgetispeed.h
--- a/libc/src/termios/cfgetispeed.h
+++ b/libc/src/termios/cfgetispeed.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-speed_t cfgetispeed(const struct termios *t);
+speed_t cfgetispeed(const struct termios *t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/termios/cfgetospeed.h b/libc/src/termios/cfgetospeed.h
--- a/libc/src/termios/cfgetospeed.h
+++ b/libc/src/termios/cfgetospeed.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-speed_t cfgetospeed(const struct termios *t);
+speed_t cfgetospeed(const struct termios *t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/termios/cfsetispeed.h b/libc/src/termios/cfsetispeed.h
--- a/libc/src/termios/cfsetispeed.h
+++ b/libc/src/termios/cfsetispeed.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int cfsetispeed(struct termios *t, speed_t speed);
+int cfsetispeed(struct termios *t, speed_t speed) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/termios/cfsetospeed.h b/libc/src/termios/cfsetospeed.h
--- a/libc/src/termios/cfsetospeed.h
+++ b/libc/src/termios/cfsetospeed.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int cfsetospeed(struct termios *t, speed_t speed);
+int cfsetospeed(struct termios *t, speed_t speed) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/termios/tcdrain.h b/libc/src/termios/tcdrain.h
--- a/libc/src/termios/tcdrain.h
+++ b/libc/src/termios/tcdrain.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int tcdrain(int fd);
+int tcdrain(int fd) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/termios/tcflow.h b/libc/src/termios/tcflow.h
--- a/libc/src/termios/tcflow.h
+++ b/libc/src/termios/tcflow.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int tcflow(int fd, int action);
+int tcflow(int fd, int action) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/termios/tcflush.h b/libc/src/termios/tcflush.h
--- a/libc/src/termios/tcflush.h
+++ b/libc/src/termios/tcflush.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int tcflush(int fd, int queue_selector);
+int tcflush(int fd, int queue_selector) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/termios/tcgetattr.h b/libc/src/termios/tcgetattr.h
--- a/libc/src/termios/tcgetattr.h
+++ b/libc/src/termios/tcgetattr.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int tcgetattr(int fd, struct termios *t);
+int tcgetattr(int fd, struct termios *t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/termios/tcgetsid.h b/libc/src/termios/tcgetsid.h
--- a/libc/src/termios/tcgetsid.h
+++ b/libc/src/termios/tcgetsid.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-pid_t tcgetsid(int fd);
+pid_t tcgetsid(int fd) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/termios/tcsendbreak.h b/libc/src/termios/tcsendbreak.h
--- a/libc/src/termios/tcsendbreak.h
+++ b/libc/src/termios/tcsendbreak.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int tcsendbreak(int fd, int duration);
+int tcsendbreak(int fd, int duration) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/termios/tcsetattr.h b/libc/src/termios/tcsetattr.h
--- a/libc/src/termios/tcsetattr.h
+++ b/libc/src/termios/tcsetattr.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int tcsetattr(int fd, int actions, const struct termios *t);
+int tcsetattr(int fd, int actions, const struct termios *t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/call_once.h b/libc/src/threads/call_once.h
--- a/libc/src/threads/call_once.h
+++ b/libc/src/threads/call_once.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void call_once(once_flag *flag, __call_once_func_t func);
+void call_once(once_flag *flag, __call_once_func_t func) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/cnd_broadcast.h b/libc/src/threads/cnd_broadcast.h
--- a/libc/src/threads/cnd_broadcast.h
+++ b/libc/src/threads/cnd_broadcast.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int cnd_broadcast(cnd_t *cond);
+int cnd_broadcast(cnd_t *cond) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/cnd_destroy.h b/libc/src/threads/cnd_destroy.h
--- a/libc/src/threads/cnd_destroy.h
+++ b/libc/src/threads/cnd_destroy.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void cnd_destroy(cnd_t *cond);
+void cnd_destroy(cnd_t *cond) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/cnd_init.h b/libc/src/threads/cnd_init.h
--- a/libc/src/threads/cnd_init.h
+++ b/libc/src/threads/cnd_init.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int cnd_init(cnd_t *cond);
+int cnd_init(cnd_t *cond) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/cnd_signal.h b/libc/src/threads/cnd_signal.h
--- a/libc/src/threads/cnd_signal.h
+++ b/libc/src/threads/cnd_signal.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int cnd_signal(cnd_t *cond);
+int cnd_signal(cnd_t *cond) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/cnd_wait.h b/libc/src/threads/cnd_wait.h
--- a/libc/src/threads/cnd_wait.h
+++ b/libc/src/threads/cnd_wait.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int cnd_wait(cnd_t *cond, mtx_t *mutex);
+int cnd_wait(cnd_t *cond, mtx_t *mutex) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/mtx_destroy.h b/libc/src/threads/mtx_destroy.h
--- a/libc/src/threads/mtx_destroy.h
+++ b/libc/src/threads/mtx_destroy.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void mtx_destroy(mtx_t *mutex);
+void mtx_destroy(mtx_t *mutex) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/mtx_init.h b/libc/src/threads/mtx_init.h
--- a/libc/src/threads/mtx_init.h
+++ b/libc/src/threads/mtx_init.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int mtx_init(mtx_t *mutex, int type);
+int mtx_init(mtx_t *mutex, int type) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/mtx_lock.h b/libc/src/threads/mtx_lock.h
--- a/libc/src/threads/mtx_lock.h
+++ b/libc/src/threads/mtx_lock.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int mtx_lock(mtx_t *mutex);
+int mtx_lock(mtx_t *mutex) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/mtx_unlock.h b/libc/src/threads/mtx_unlock.h
--- a/libc/src/threads/mtx_unlock.h
+++ b/libc/src/threads/mtx_unlock.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int mtx_unlock(mtx_t *mutex);
+int mtx_unlock(mtx_t *mutex) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/thrd_create.h b/libc/src/threads/thrd_create.h
--- a/libc/src/threads/thrd_create.h
+++ b/libc/src/threads/thrd_create.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int thrd_create(thrd_t *thread, thrd_start_t func, void *arg);
+int thrd_create(thrd_t *thread, thrd_start_t func, void *arg) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/thrd_current.h b/libc/src/threads/thrd_current.h
--- a/libc/src/threads/thrd_current.h
+++ b/libc/src/threads/thrd_current.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-thrd_t thrd_current();
+thrd_t thrd_current() noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/thrd_detach.h b/libc/src/threads/thrd_detach.h
--- a/libc/src/threads/thrd_detach.h
+++ b/libc/src/threads/thrd_detach.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int thrd_detach(thrd_t thread);
+int thrd_detach(thrd_t thread) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/thrd_equal.h b/libc/src/threads/thrd_equal.h
--- a/libc/src/threads/thrd_equal.h
+++ b/libc/src/threads/thrd_equal.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int thrd_equal(thrd_t lhs, thrd_t rhs);
+int thrd_equal(thrd_t lhs, thrd_t rhs) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/thrd_exit.h b/libc/src/threads/thrd_exit.h
--- a/libc/src/threads/thrd_exit.h
+++ b/libc/src/threads/thrd_exit.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void thrd_exit(int retval);
+void thrd_exit(int retval) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/thrd_join.h b/libc/src/threads/thrd_join.h
--- a/libc/src/threads/thrd_join.h
+++ b/libc/src/threads/thrd_join.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int thrd_join(thrd_t thread, int *retval);
+int thrd_join(thrd_t thread, int *retval) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/tss_create.h b/libc/src/threads/tss_create.h
--- a/libc/src/threads/tss_create.h
+++ b/libc/src/threads/tss_create.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int tss_create(tss_t *key, tss_dtor_t dtor);
+int tss_create(tss_t *key, tss_dtor_t dtor) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/tss_delete.h b/libc/src/threads/tss_delete.h
--- a/libc/src/threads/tss_delete.h
+++ b/libc/src/threads/tss_delete.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void tss_delete(tss_t key);
+void tss_delete(tss_t key) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/tss_get.h b/libc/src/threads/tss_get.h
--- a/libc/src/threads/tss_get.h
+++ b/libc/src/threads/tss_get.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-void *tss_get(pthread_key_t);
+void *tss_get(pthread_key_t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/threads/tss_set.h b/libc/src/threads/tss_set.h
--- a/libc/src/threads/tss_set.h
+++ b/libc/src/threads/tss_set.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int tss_set(tss_t, void *);
+int tss_set(tss_t, void *) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/time/asctime.h b/libc/src/time/asctime.h
--- a/libc/src/time/asctime.h
+++ b/libc/src/time/asctime.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-char *asctime(const struct tm *timeptr);
+char *asctime(const struct tm *timeptr) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/time/asctime_r.h b/libc/src/time/asctime_r.h
--- a/libc/src/time/asctime_r.h
+++ b/libc/src/time/asctime_r.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-char *asctime_r(const struct tm *timeptr, char *buffer);
+char *asctime_r(const struct tm *timeptr, char *buffer) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/time/clock.h b/libc/src/time/clock.h
--- a/libc/src/time/clock.h
+++ b/libc/src/time/clock.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-clock_t clock();
+clock_t clock() noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/time/clock_gettime.h b/libc/src/time/clock_gettime.h
--- a/libc/src/time/clock_gettime.h
+++ b/libc/src/time/clock_gettime.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int clock_gettime(clockid_t clockid, struct timespec *tp);
+int clock_gettime(clockid_t clockid, struct timespec *tp) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/time/difftime.h b/libc/src/time/difftime.h
--- a/libc/src/time/difftime.h
+++ b/libc/src/time/difftime.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-double difftime(time_t end, time_t beginning);
+double difftime(time_t end, time_t beginning) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/time/gettimeofday.h b/libc/src/time/gettimeofday.h
--- a/libc/src/time/gettimeofday.h
+++ b/libc/src/time/gettimeofday.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int gettimeofday(struct timeval *tv, void *tz);
+int gettimeofday(struct timeval *tv, void *tz) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/time/gmtime.h b/libc/src/time/gmtime.h
--- a/libc/src/time/gmtime.h
+++ b/libc/src/time/gmtime.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-struct tm *gmtime(const time_t *timer);
+struct tm *gmtime(const time_t *timer) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/time/gmtime_r.h b/libc/src/time/gmtime_r.h
--- a/libc/src/time/gmtime_r.h
+++ b/libc/src/time/gmtime_r.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-struct tm *gmtime_r(const time_t *timer, struct tm *result);
+struct tm *gmtime_r(const time_t *timer, struct tm *result) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/time/mktime.h b/libc/src/time/mktime.h
--- a/libc/src/time/mktime.h
+++ b/libc/src/time/mktime.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-time_t mktime(struct tm *t1);
+time_t mktime(struct tm *t1) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/time/nanosleep.h b/libc/src/time/nanosleep.h
--- a/libc/src/time/nanosleep.h
+++ b/libc/src/time/nanosleep.h
@@ -14,7 +14,7 @@
 
 namespace __llvm_libc {
 
-int nanosleep(const struct timespec *req, struct timespec *rem);
+int nanosleep(const struct timespec *req, struct timespec *rem) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/time/time_func.h b/libc/src/time/time_func.h
--- a/libc/src/time/time_func.h
+++ b/libc/src/time/time_func.h
@@ -15,7 +15,7 @@
 // public header file time.h.
 namespace __llvm_libc {
 
-time_t time(time_t *tp);
+time_t time(time_t *tp) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/access.h b/libc/src/unistd/access.h
--- a/libc/src/unistd/access.h
+++ b/libc/src/unistd/access.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int access(const char *path, int mode);
+int access(const char *path, int mode) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/chdir.h b/libc/src/unistd/chdir.h
--- a/libc/src/unistd/chdir.h
+++ b/libc/src/unistd/chdir.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int chdir(const char *path);
+int chdir(const char *path) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/close.h b/libc/src/unistd/close.h
--- a/libc/src/unistd/close.h
+++ b/libc/src/unistd/close.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int close(int fd);
+int close(int fd) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/dup.h b/libc/src/unistd/dup.h
--- a/libc/src/unistd/dup.h
+++ b/libc/src/unistd/dup.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int dup(int fd);
+int dup(int fd) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/dup2.h b/libc/src/unistd/dup2.h
--- a/libc/src/unistd/dup2.h
+++ b/libc/src/unistd/dup2.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int dup2(int oldfd, int newfd);
+int dup2(int oldfd, int newfd) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/dup3.h b/libc/src/unistd/dup3.h
--- a/libc/src/unistd/dup3.h
+++ b/libc/src/unistd/dup3.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int dup3(int oldfd, int newfd, int flags);
+int dup3(int oldfd, int newfd, int flags) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/execv.h b/libc/src/unistd/execv.h
--- a/libc/src/unistd/execv.h
+++ b/libc/src/unistd/execv.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int execv(const char *path, char *const argv[]);
+int execv(const char *path, char *const argv[]) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/execve.h b/libc/src/unistd/execve.h
--- a/libc/src/unistd/execve.h
+++ b/libc/src/unistd/execve.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int execve(const char *path, char *const argv[], char *const envp[]);
+int execve(const char *path, char *const argv[], char *const envp[]) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/fchdir.h b/libc/src/unistd/fchdir.h
--- a/libc/src/unistd/fchdir.h
+++ b/libc/src/unistd/fchdir.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int fchdir(int fd);
+int fchdir(int fd) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/fork.h b/libc/src/unistd/fork.h
--- a/libc/src/unistd/fork.h
+++ b/libc/src/unistd/fork.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-pid_t fork();
+pid_t fork() noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/fsync.h b/libc/src/unistd/fsync.h
--- a/libc/src/unistd/fsync.h
+++ b/libc/src/unistd/fsync.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int fsync(int fd);
+int fsync(int fd) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/ftruncate.h b/libc/src/unistd/ftruncate.h
--- a/libc/src/unistd/ftruncate.h
+++ b/libc/src/unistd/ftruncate.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int ftruncate(int, off_t);
+int ftruncate(int, off_t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/getcwd.h b/libc/src/unistd/getcwd.h
--- a/libc/src/unistd/getcwd.h
+++ b/libc/src/unistd/getcwd.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-char *getcwd(char *buf, size_t size);
+char *getcwd(char *buf, size_t size) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/geteuid.h b/libc/src/unistd/geteuid.h
--- a/libc/src/unistd/geteuid.h
+++ b/libc/src/unistd/geteuid.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-uid_t geteuid();
+uid_t geteuid() noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/getopt.h b/libc/src/unistd/getopt.h
--- a/libc/src/unistd/getopt.h
+++ b/libc/src/unistd/getopt.h
@@ -15,10 +15,10 @@
 namespace __llvm_libc {
 
 namespace impl {
-void set_getopt_state(char **, int *, int *, unsigned *, int, FILE *);
+void set_getopt_state(char **, int *, int *, unsigned *, int, FILE *) noexcept;
 }
 
-int getopt(int argc, char *const argv[], const char *optstring);
+int getopt(int argc, char *const argv[], const char *optstring) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/getopt.cpp b/libc/src/unistd/getopt.cpp
--- a/libc/src/unistd/getopt.cpp
+++ b/libc/src/unistd/getopt.cpp
@@ -185,7 +185,7 @@
 #ifndef LLVM_LIBC_PUBLIC_PACKAGING
 // This is used exclusively in tests.
 void set_getopt_state(char **optarg, int *optind, int *optopt, unsigned *optpos,
-                      int opterr, FILE *errstream) {
+                      int opterr, FILE *errstream) noexcept {
   ctx = {optarg, optind, optopt, optpos, opterr, errstream};
 }
 #endif
diff --git a/libc/src/unistd/getpid.h b/libc/src/unistd/getpid.h
--- a/libc/src/unistd/getpid.h
+++ b/libc/src/unistd/getpid.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-pid_t getpid();
+pid_t getpid() noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/getppid.h b/libc/src/unistd/getppid.h
--- a/libc/src/unistd/getppid.h
+++ b/libc/src/unistd/getppid.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-pid_t getppid();
+pid_t getppid() noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/getuid.h b/libc/src/unistd/getuid.h
--- a/libc/src/unistd/getuid.h
+++ b/libc/src/unistd/getuid.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-uid_t getuid();
+uid_t getuid() noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/isatty.h b/libc/src/unistd/isatty.h
--- a/libc/src/unistd/isatty.h
+++ b/libc/src/unistd/isatty.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int isatty(int fd);
+int isatty(int fd) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/link.h b/libc/src/unistd/link.h
--- a/libc/src/unistd/link.h
+++ b/libc/src/unistd/link.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int link(const char *, const char *);
+int link(const char *, const char *) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/linkat.h b/libc/src/unistd/linkat.h
--- a/libc/src/unistd/linkat.h
+++ b/libc/src/unistd/linkat.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int linkat(int, const char *, int, const char *, int);
+int linkat(int, const char *, int, const char *, int) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/lseek.h b/libc/src/unistd/lseek.h
--- a/libc/src/unistd/lseek.h
+++ b/libc/src/unistd/lseek.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-off_t lseek(int fd, off_t offset, int whence);
+off_t lseek(int fd, off_t offset, int whence) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/pread.h b/libc/src/unistd/pread.h
--- a/libc/src/unistd/pread.h
+++ b/libc/src/unistd/pread.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-ssize_t pread(int fd, void *buf, size_t count, off_t offset);
+ssize_t pread(int fd, void *buf, size_t count, off_t offset) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/pwrite.h b/libc/src/unistd/pwrite.h
--- a/libc/src/unistd/pwrite.h
+++ b/libc/src/unistd/pwrite.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset);
+ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/read.h b/libc/src/unistd/read.h
--- a/libc/src/unistd/read.h
+++ b/libc/src/unistd/read.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-ssize_t read(int fd, void *buf, size_t count);
+ssize_t read(int fd, void *buf, size_t count) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/readlink.h b/libc/src/unistd/readlink.h
--- a/libc/src/unistd/readlink.h
+++ b/libc/src/unistd/readlink.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-ssize_t readlink(const char *__restrict, char *__restrict, size_t);
+ssize_t readlink(const char *__restrict, char *__restrict, size_t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/readlinkat.h b/libc/src/unistd/readlinkat.h
--- a/libc/src/unistd/readlinkat.h
+++ b/libc/src/unistd/readlinkat.h
@@ -13,7 +13,8 @@
 
 namespace __llvm_libc {
 
-ssize_t readlinkat(int, const char *__restrict, char *__restrict, size_t);
+ssize_t readlinkat(int, const char *__restrict, char *__restrict,
+                   size_t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/rmdir.h b/libc/src/unistd/rmdir.h
--- a/libc/src/unistd/rmdir.h
+++ b/libc/src/unistd/rmdir.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int rmdir(const char *path);
+int rmdir(const char *path) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/symlink.h b/libc/src/unistd/symlink.h
--- a/libc/src/unistd/symlink.h
+++ b/libc/src/unistd/symlink.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int symlink(const char *, const char *);
+int symlink(const char *, const char *) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/symlinkat.h b/libc/src/unistd/symlinkat.h
--- a/libc/src/unistd/symlinkat.h
+++ b/libc/src/unistd/symlinkat.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int symlinkat(const char *, int, const char *);
+int symlinkat(const char *, int, const char *) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/syscall.h b/libc/src/unistd/syscall.h
--- a/libc/src/unistd/syscall.h
+++ b/libc/src/unistd/syscall.h
@@ -15,7 +15,7 @@
 namespace __llvm_libc {
 
 long __llvm_libc_syscall(long number, long arg1, long arg2, long arg3,
-                         long arg4, long arg5, long arg6);
+                         long arg4, long arg5, long arg6) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/sysconf.h b/libc/src/unistd/sysconf.h
--- a/libc/src/unistd/sysconf.h
+++ b/libc/src/unistd/sysconf.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-long sysconf(int name);
+long sysconf(int name) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/truncate.h b/libc/src/unistd/truncate.h
--- a/libc/src/unistd/truncate.h
+++ b/libc/src/unistd/truncate.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-int truncate(const char *, off_t);
+int truncate(const char *, off_t) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/unlink.h b/libc/src/unistd/unlink.h
--- a/libc/src/unistd/unlink.h
+++ b/libc/src/unistd/unlink.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int unlink(const char *path);
+int unlink(const char *path) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/unlinkat.h b/libc/src/unistd/unlinkat.h
--- a/libc/src/unistd/unlinkat.h
+++ b/libc/src/unistd/unlinkat.h
@@ -11,7 +11,7 @@
 
 namespace __llvm_libc {
 
-int unlinkat(int dfd, const char *path, int flags);
+int unlinkat(int dfd, const char *path, int flags) noexcept;
 
 } // namespace __llvm_libc
 
diff --git a/libc/src/unistd/write.h b/libc/src/unistd/write.h
--- a/libc/src/unistd/write.h
+++ b/libc/src/unistd/write.h
@@ -13,7 +13,7 @@
 
 namespace __llvm_libc {
 
-ssize_t write(int fd, const void *buf, size_t count);
+ssize_t write(int fd, const void *buf, size_t count) noexcept;
 
 } // namespace __llvm_libc