diff --git a/libc/src/__support/File/CMakeLists.txt b/libc/src/__support/File/CMakeLists.txt
--- a/libc/src/__support/File/CMakeLists.txt
+++ b/libc/src/__support/File/CMakeLists.txt
@@ -35,20 +35,32 @@
 endif()
 
 add_subdirectory(${LIBC_TARGET_OS})
-set(target_file libc.src.__support.File.${LIBC_TARGET_OS}.${LIBC_TARGET_OS}_file)
+
+set(target_file libc.src.__support.File.${LIBC_TARGET_OS}.file)
+set(target_stdout libc.src.__support.File.${LIBC_TARGET_OS}.stdout)
+set(target_stderr libc.src.__support.File.${LIBC_TARGET_OS}.stderr)
+set(target_stdin libc.src.__support.File.${LIBC_TARGET_OS}.stdin)
+
+set(file_targets "${target_file};${target_stdout};${target_stdin};${target_stderr}")
+set(file_aliases "platform_file;platform_stdout;platform_stdin;platform_stderr")
+
+foreach(alias target IN ZIP_LISTS file_aliases file_targets)
+  if(TARGET ${target})
+    add_object_library(
+      ${alias}
+      ALIAS
+        ${target}
+      DEPENDS
+        ${target}
+    )
+  endif()
+endforeach()
+
 set(target_dir libc.src.__support.File.${LIBC_TARGET_OS}.${LIBC_TARGET_OS}_dir)
-if((NOT TARGET ${target_file}) OR (NOT TARGET ${target_dir}))
+if(NOT TARGET ${target_dir})
   return()
 endif()
 
-add_object_library(
-  platform_file
-  ALIAS
-    ${target_file}
-  DEPENDS
-    ${target_file}
-)
-
 add_object_library(
   platform_dir
   ALIAS
diff --git a/libc/src/__support/File/linux/CMakeLists.txt b/libc/src/__support/File/linux/CMakeLists.txt
--- a/libc/src/__support/File/linux/CMakeLists.txt
+++ b/libc/src/__support/File/linux/CMakeLists.txt
@@ -1,7 +1,9 @@
 add_object_library(
-  linux_file
+  file
   SRCS
     file.cpp
+  HDRS
+    file.h
   DEPENDS
     libc.include.fcntl
     libc.include.stdio
@@ -13,6 +15,30 @@
     libc.src.__support.File.file
 )
 
+add_object_library(
+  stdout
+  SRCS
+    stdout.cpp
+  DEPENDS
+    .file
+)
+
+add_object_library(
+  stdin
+  SRCS
+    stdin.cpp
+  DEPENDS
+    .file
+)
+
+add_object_library(
+  stderr
+  SRCS
+    stderr.cpp
+  DEPENDS
+    .file
+)
+
 add_object_library(
   linux_dir
   SRCS
diff --git a/libc/src/__support/File/linux/file.h b/libc/src/__support/File/linux/file.h
new file mode 100644
--- /dev/null
+++ b/libc/src/__support/File/linux/file.h
@@ -0,0 +1,32 @@
+//===--- Linux specialization of the File data structure ------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/File/file.h"
+
+namespace __llvm_libc {
+
+FileIOResult linux_file_write(File *, const void *, size_t);
+FileIOResult linux_file_read(File *, void *, size_t);
+ErrorOr<long> linux_file_seek(File *, long, int);
+int linux_file_close(File *);
+
+class LinuxFile : public File {
+  int fd;
+
+public:
+  constexpr LinuxFile(int file_descriptor, uint8_t *buffer, size_t buffer_size,
+                      int buffer_mode, bool owned, File::ModeFlags modeflags)
+      : File(&linux_file_write, &linux_file_read, &linux_file_seek,
+             &linux_file_close, buffer, buffer_size, buffer_mode, owned,
+             modeflags),
+        fd(file_descriptor) {}
+
+  int get_fd() const { return fd; }
+};
+
+} // namespace __llvm_libc
diff --git a/libc/src/__support/File/linux/file.cpp b/libc/src/__support/File/linux/file.cpp
--- a/libc/src/__support/File/linux/file.cpp
+++ b/libc/src/__support/File/linux/file.cpp
@@ -1,4 +1,4 @@
-//===--- Linux specialization of the File data structure ------------------===//
+//===--- Implementation of the Linux specialization of File ---------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "file.h"
+
 #include "src/__support/File/file.h"
 
 #include "src/__support/CPP/new.h"
@@ -18,31 +20,7 @@
 
 namespace __llvm_libc {
 
-namespace {
-
-FileIOResult write_func(File *, const void *, size_t);
-FileIOResult read_func(File *, void *, size_t);
-ErrorOr<long> seek_func(File *, long, int);
-int close_func(File *);
-
-} // anonymous namespace
-
-class LinuxFile : public File {
-  int fd;
-
-public:
-  constexpr LinuxFile(int file_descriptor, uint8_t *buffer, size_t buffer_size,
-                      int buffer_mode, bool owned, File::ModeFlags modeflags)
-      : File(&write_func, &read_func, &seek_func, &close_func, buffer,
-             buffer_size, buffer_mode, owned, modeflags),
-        fd(file_descriptor) {}
-
-  int get_fd() const { return fd; }
-};
-
-namespace {
-
-FileIOResult write_func(File *f, const void *data, size_t size) {
+FileIOResult linux_file_write(File *f, const void *data, size_t size) {
   auto *lf = reinterpret_cast<LinuxFile *>(f);
   int ret = __llvm_libc::syscall_impl<int>(SYS_write, lf->get_fd(), data, size);
   if (ret < 0) {
@@ -51,7 +29,7 @@
   return ret;
 }
 
-FileIOResult read_func(File *f, void *buf, size_t size) {
+FileIOResult linux_file_read(File *f, void *buf, size_t size) {
   auto *lf = reinterpret_cast<LinuxFile *>(f);
   int ret = __llvm_libc::syscall_impl<int>(SYS_read, lf->get_fd(), buf, size);
   if (ret < 0) {
@@ -60,7 +38,7 @@
   return ret;
 }
 
-ErrorOr<long> seek_func(File *f, long offset, int whence) {
+ErrorOr<long> linux_file_seek(File *f, long offset, int whence) {
   auto *lf = reinterpret_cast<LinuxFile *>(f);
   long result;
 #ifdef SYS_lseek
@@ -90,7 +68,7 @@
   return result;
 }
 
-int close_func(File *f) {
+int linux_file_close(File *f) {
   auto *lf = reinterpret_cast<LinuxFile *>(f);
   int ret = __llvm_libc::syscall_impl<int>(SYS_close, lf->get_fd());
   if (ret < 0) {
@@ -100,8 +78,6 @@
   return 0;
 }
 
-} // anonymous namespace
-
 ErrorOr<File *> openfile(const char *path, const char *mode) {
   using ModeFlags = File::ModeFlags;
   auto modeflags = File::mode_flags(mode);
@@ -166,28 +142,4 @@
   return lf->get_fd();
 }
 
-constexpr size_t STDIN_BUFFER_SIZE = 512;
-uint8_t stdin_buffer[STDIN_BUFFER_SIZE];
-static LinuxFile StdIn(0, stdin_buffer, STDIN_BUFFER_SIZE, _IOFBF, false,
-                       File::ModeFlags(File::OpenMode::READ));
-File *stdin = &StdIn;
-
-constexpr size_t STDOUT_BUFFER_SIZE = 1024;
-uint8_t stdout_buffer[STDOUT_BUFFER_SIZE];
-static LinuxFile StdOut(1, stdout_buffer, STDOUT_BUFFER_SIZE, _IOLBF, false,
-                        File::ModeFlags(File::OpenMode::APPEND));
-File *stdout = &StdOut;
-
-constexpr size_t STDERR_BUFFER_SIZE = 0;
-static LinuxFile StdErr(2, nullptr, STDERR_BUFFER_SIZE, _IONBF, false,
-                        File::ModeFlags(File::OpenMode::APPEND));
-File *stderr = &StdErr;
-
 } // namespace __llvm_libc
-
-// Provide the external defintitions of the standard IO streams.
-extern "C" {
-FILE *stdin = reinterpret_cast<FILE *>(&__llvm_libc::StdIn);
-FILE *stderr = reinterpret_cast<FILE *>(&__llvm_libc::StdErr);
-FILE *stdout = reinterpret_cast<FILE *>(&__llvm_libc::StdOut);
-}
diff --git a/libc/src/__support/File/linux/stderr.cpp b/libc/src/__support/File/linux/stderr.cpp
new file mode 100644
--- /dev/null
+++ b/libc/src/__support/File/linux/stderr.cpp
@@ -0,0 +1,23 @@
+//===--- Definition of Linux stderr ---------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "file.h"
+#include <stdio.h>
+
+namespace __llvm_libc {
+
+constexpr size_t STDERR_BUFFER_SIZE = 0;
+static LinuxFile StdErr(2, nullptr, STDERR_BUFFER_SIZE, _IONBF, false,
+                        File::ModeFlags(File::OpenMode::APPEND));
+File *stderr = &StdErr;
+
+} // namespace __llvm_libc
+
+extern "C" {
+FILE *stderr = reinterpret_cast<FILE *>(&__llvm_libc::StdErr);
+}
diff --git a/libc/src/__support/File/linux/stdin.cpp b/libc/src/__support/File/linux/stdin.cpp
new file mode 100644
--- /dev/null
+++ b/libc/src/__support/File/linux/stdin.cpp
@@ -0,0 +1,24 @@
+//===--- Definition of Linux stdin ----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "file.h"
+#include <stdio.h>
+
+namespace __llvm_libc {
+
+constexpr size_t STDIN_BUFFER_SIZE = 512;
+uint8_t stdin_buffer[STDIN_BUFFER_SIZE];
+static LinuxFile StdIn(0, stdin_buffer, STDIN_BUFFER_SIZE, _IOFBF, false,
+                       File::ModeFlags(File::OpenMode::READ));
+File *stdin = &StdIn;
+
+} // namespace __llvm_libc
+
+extern "C" {
+FILE *stdin = reinterpret_cast<FILE *>(&__llvm_libc::StdIn);
+} // extern "C"
diff --git a/libc/src/__support/File/linux/stdout.cpp b/libc/src/__support/File/linux/stdout.cpp
new file mode 100644
--- /dev/null
+++ b/libc/src/__support/File/linux/stdout.cpp
@@ -0,0 +1,24 @@
+//===--- Definition of Linux stdout ---------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "file.h"
+#include <stdio.h>
+
+namespace __llvm_libc {
+
+constexpr size_t STDOUT_BUFFER_SIZE = 1024;
+uint8_t stdout_buffer[STDOUT_BUFFER_SIZE];
+static LinuxFile StdOut(1, stdout_buffer, STDOUT_BUFFER_SIZE, _IOLBF, false,
+                        File::ModeFlags(File::OpenMode::APPEND));
+File *stdout = &StdOut;
+
+} // namespace __llvm_libc
+
+extern "C" {
+FILE *stdout = reinterpret_cast<FILE *>(&__llvm_libc::StdOut);
+} // extern "C"
diff --git a/libc/src/stdio/CMakeLists.txt b/libc/src/stdio/CMakeLists.txt
--- a/libc/src/stdio/CMakeLists.txt
+++ b/libc/src/stdio/CMakeLists.txt
@@ -422,6 +422,7 @@
  list(APPEND printf_deps
       libc.src.__support.File.file
       libc.src.__support.File.platform_file
+      libc.src.__support.File.platform_stdout
   )
 else()
  set(printf_copts "-DLIBC_COPT_PRINTF_USE_SYSTEM_FILE")
diff --git a/libc/src/stdio/generic/CMakeLists.txt b/libc/src/stdio/generic/CMakeLists.txt
--- a/libc/src/stdio/generic/CMakeLists.txt
+++ b/libc/src/stdio/generic/CMakeLists.txt
@@ -72,7 +72,7 @@
     libc.src.errno.errno
     libc.include.stdio
     libc.src.__support.File.file
-    libc.src.__support.File.platform_file
+    libc.src.__support.File.platform_stdout
 )
 
 add_entrypoint_object(
@@ -84,7 +84,7 @@
   DEPENDS
     libc.include.stdio
     libc.src.__support.File.file
-    libc.src.__support.File.platform_file
+    libc.src.__support.File.platform_stdin
 )
 
 add_entrypoint_object(
@@ -96,7 +96,7 @@
   DEPENDS
     libc.include.stdio
     libc.src.__support.File.file
-    libc.src.__support.File.platform_file
+    libc.src.__support.File.platform_stdout
 )
 
 add_entrypoint_object(
@@ -108,5 +108,5 @@
   DEPENDS
     libc.include.stdio
     libc.src.__support.File.file
-    libc.src.__support.File.platform_file
+    libc.src.__support.File.platform_stderr
 )
diff --git a/libc/src/unistd/CMakeLists.txt b/libc/src/unistd/CMakeLists.txt
--- a/libc/src/unistd/CMakeLists.txt
+++ b/libc/src/unistd/CMakeLists.txt
@@ -266,6 +266,7 @@
     libc.src.__support.CPP.optional
     libc.src.__support.CPP.string_view
     libc.src.__support.File.file
+    libc.src.__support.File.platform_stderr
     libc.src.stdio.fprintf
 )
 
diff --git a/libc/test/src/__support/File/CMakeLists.txt b/libc/test/src/__support/File/CMakeLists.txt
--- a/libc/test/src/__support/File/CMakeLists.txt
+++ b/libc/test/src/__support/File/CMakeLists.txt
@@ -21,18 +21,34 @@
     libc.src.__support.File.file
 )
 
-if (TARGET libc.src.__support.File.platform_file)
-  add_libc_test(
-    platform_file_test
-    SUITE
-      libc-support-tests
-    SRCS
-      platform_file_test.cpp
-    DEPENDS
-      libc.src.__support.File.file
-      libc.src.__support.File.platform_file
-      libc.include.stdio
-  )
-endif()
+add_libc_test(
+  platform_file_test
+  SUITE
+    libc-support-tests
+  SRCS
+    platform_file_test.cpp
+  DEPENDS
+    libc.src.__support.File.file
+    libc.src.__support.File.platform_file
+    libc.include.stdio
+)
+
+set(platform_stream_targets "platform_stdout;platform_stdin;platform_stderr")
+foreach(target IN LISTS platform_file_targets)
+  if(TARGET libc.src.__support.File.${target})
+    add_libc_test(
+      ${target}_test
+      HERMETIC_TEST_ONLY
+      SUITE
+        libc-support-tests
+      SRCS
+        ${target}_test.cpp
+      DEPENDS
+        libc.src.__support.File.file
+        libc.src.__support.File.${target}
+        libc.include.stdio
+    )
+  endif()
+endforeach()
 
 add_subdirectory(testdata)
diff --git a/libc/test/src/__support/File/platform_file_test.cpp b/libc/test/src/__support/File/platform_file_test.cpp
--- a/libc/test/src/__support/File/platform_file_test.cpp
+++ b/libc/test/src/__support/File/platform_file_test.cpp
@@ -201,8 +201,3 @@
   ASSERT_TRUE(file->error());
   ASSERT_EQ(file->close(), 0);
 }
-
-TEST(LlvmLibcPlatformFileTest, StdOutStdErrSmokeTest) {
-  EXPECT_FALSE(__llvm_libc::stdout == nullptr);
-  EXPECT_FALSE(__llvm_libc::stderr == nullptr);
-}
diff --git a/libc/test/src/__support/File/platform_stderr_test.cpp b/libc/test/src/__support/File/platform_stderr_test.cpp
new file mode 100644
--- /dev/null
+++ b/libc/test/src/__support/File/platform_stderr_test.cpp
@@ -0,0 +1,12 @@
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/File/file.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcPlatformStreamTest, StdErrSmokeTest) {
+  EXPECT_FALSE(__llvm_libc::stderr == nullptr);
+}
diff --git a/libc/test/src/__support/File/platform_stdin_test.cpp b/libc/test/src/__support/File/platform_stdin_test.cpp
new file mode 100644
--- /dev/null
+++ b/libc/test/src/__support/File/platform_stdin_test.cpp
@@ -0,0 +1,12 @@
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/File/file.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcPlatformStreamTest, StdInSmokeTest) {
+  EXPECT_FALSE(__llvm_libc::stdin == nullptr);
+}
diff --git a/libc/test/src/__support/File/platform_stdout_test.cpp b/libc/test/src/__support/File/platform_stdout_test.cpp
new file mode 100644
--- /dev/null
+++ b/libc/test/src/__support/File/platform_stdout_test.cpp
@@ -0,0 +1,12 @@
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/File/file.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcPlatformStreamTest, StdOutSmokeTest) {
+  EXPECT_FALSE(__llvm_libc::stdout == nullptr);
+}
diff --git a/libc/test/src/stdio/CMakeLists.txt b/libc/test/src/stdio/CMakeLists.txt
--- a/libc/test/src/stdio/CMakeLists.txt
+++ b/libc/test/src/stdio/CMakeLists.txt
@@ -136,13 +136,16 @@
 )
 
 if(LLVM_LIBC_FULL_BUILD)
-# In fullbuild mode, fprintf's tests use the internal FILE for other functions.
- list(APPEND fprintf_test_deps
-      libc.src.stdio.fclose
-      libc.src.stdio.ferror
-      libc.src.stdio.fopen
-      libc.src.stdio.fread
+  # In fullbuild mode, fprintf's tests use the internal FILE for other functions.
+  list(APPEND fprintf_test_deps
+       libc.src.stdio.fclose
+       libc.src.stdio.ferror
+       libc.src.stdio.fopen
+       libc.src.stdio.fread
   )
+  # This is to be used for tests which write to libc's platform streams
+  # under full build but write to system-lib's streams otherwise.
+  set(hermetic_test_only HERMETIC_TEST_ONLY)
 else()
 # Else in overlay mode they use the system's FILE.
  set(fprintf_test_copts "-DLIBC_COPT_PRINTF_USE_SYSTEM_FILE")
@@ -161,8 +164,9 @@
     ${fprintf_test_copts}
 )
 
-add_libc_unittest(
+add_libc_test(
   printf_test
+  ${hermetic_test_only}
   SUITE
     libc_stdio_unittests
   SRCS
@@ -205,8 +209,9 @@
     ${fprintf_test_copts}
 )
 
-add_libc_unittest(
+add_libc_test(
   vprintf_test
+  ${hermetic_test_only}
   SUITE
     libc_stdio_unittests
   SRCS
@@ -244,6 +249,7 @@
 
 add_libc_test(
   puts_test
+  HERMETIC_TEST_ONLY # writes to libc's stdout
   SUITE
     libc_stdio_unittests
   SRCS
@@ -254,6 +260,7 @@
 
 add_libc_test(
   fputs_test
+  HERMETIC_TEST_ONLY # writes to libc's stdout and stderr
   SUITE
     libc_stdio_unittests
   SRCS
diff --git a/libc/test/src/unistd/CMakeLists.txt b/libc/test/src/unistd/CMakeLists.txt
--- a/libc/test/src/unistd/CMakeLists.txt
+++ b/libc/test/src/unistd/CMakeLists.txt
@@ -430,8 +430,9 @@
     libc.src.unistd.sysconf
 )
 
-add_libc_unittest(
+add_libc_test(
   getopt_test
+  HERMETIC_TEST_ONLY # Uses libc's own stderr
   SUITE
     libc_unistd_unittests
   SRCS
diff --git a/libc/test/src/unistd/getopt_test.cpp b/libc/test/src/unistd/getopt_test.cpp
--- a/libc/test/src/unistd/getopt_test.cpp
+++ b/libc/test/src/unistd/getopt_test.cpp
@@ -34,27 +34,25 @@
       &test_globals::optpos, &test_globals::opterr, errstream);
 }
 
+static void my_memcpy(char *dest, const char *src, size_t size) {
+  for (size_t i = 0; i < size; i++)
+    dest[i] = src[i];
+}
+
+ssize_t cookie_write(void *cookie, const char *buf, size_t size) {
+  char **pos = static_cast<char **>(cookie);
+  my_memcpy(*pos, buf, size);
+  *pos += size;
+  return size;
+}
+
+static cookie_io_functions_t cookie{nullptr, &cookie_write, nullptr, nullptr};
+
 // TODO: <stdio> could be either llvm-libc's or the system libc's. The former
 // doesn't currently support fmemopen but does have fopencookie. In the future
 // just use that instead. This memopen does no error checking for the size
 // of the buffer, etc.
-FILE *memopen(char **pos) {
-  static auto memcpy = [](char *dest, const char *src, size_t size) {
-    for (size_t i = 0; i < size; i++)
-      dest[i] = src[i];
-  };
-
-  static auto *write =
-      +[](void *cookie, const char *buf, size_t size) -> ssize_t {
-    char **pos = static_cast<char **>(cookie);
-    memcpy(*pos, buf, size);
-    *pos += size;
-    return size;
-  };
-
-  static cookie_io_functions_t cookie{nullptr, write, nullptr, nullptr};
-  return __llvm_libc::fopencookie(pos, "w", cookie);
-}
+FILE *memopen(char **pos) { return __llvm_libc::fopencookie(pos, "w", cookie); }
 
 struct LlvmLibcGetoptTest : public __llvm_libc::testing::Test {
   FILE *errstream;