[libc] Add initial assert definition

[abrachet]

Summary

This patch adds a temporary __assert_fail and assert definition to make it available to internal llvm libc code. __assert_fail writes to fd 2 directly instead of stderr, using SYS_write. I have not put it in its own linux directory because this is temporary and it should be using stdio's api in the future. It does not currently print out the line number (although we could do that by stringifying __LINE__ if reviewers wish).

[abrachet]

libc/test/src/assert/assert_test.cpp

17

Should we close standard streams in death tests so it doesn't print to the terminal?

[sivachandra]

Did not do a proper review. Left couple of very high level comments.

libc/src/assert/__assert_fail.cpp

2

Looks like this is a linux only solution so should sit in a linux specific area. Or, is it because it is a temporary solution, and you envision that the final implementation would use stderr and make it platform independent?

20

Can you add to the comment how the final solution is going to look like?

[sivachandra]

libc/src/assert/__assert_fail.cpp

2

Ah, scrub this. I missed the message in the summary.

[sivachandra]

libc/config/linux/api.td

62

I think extern C for c++ is missing here.

69

Why not the assert macro?

72

Instead, we should define the assert macro as:

#ifdef __cplusplus
extern C
#endif
void __assert_fail(...); // Don't use size_t for arg types
#define assert ...
#endif

libc/spec/stdc.td

29

This is implementation detail so should not be listed here.

[abrachet]

• Prefer unsigned over size_t
• Remove __assert_fail from stdc.td
• Add comment to __assert_fail.cpp

[abrachet]

libc/config/linux/api.td

62

I'll add just commit this outside of this patch to not mess with the diff.

69

assert shouldn't be inside the include guards of assert.h so I think it needs to be handwritten in assert.h.def

72

Same as above. For reference the generated header looks like

//===---------------- C standard library header assert.h ------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIBC_ASSERT_H
#define LLVM_LIBC_ASSERT_H

#include <__llvm-libc-common.h>

#ifndef __cplusplus
#define static_assert _Static_assert
#endif

__BEGIN_C_DECLS

__END_C_DECLS

#ifdef __cplusplus
extern "C"
#endif
_Noreturn void __assert_fail(const char *, const char *, 
                             unsigned, const char *);

#endif // LLVM_LIBC_ASSERT_H

// This file may be usefully included multiple times to change assert()'s
// definition based on NDEBUG.

#undef assert

#ifdef NDEBUG
#define assert(e) (void)0
#else
#define assert(e) \
    ((e) ? (void)0 : __assert_fail(#e, __FILE__, __LINE__, __PRETTY_FUNCTION__))
#endif

[sivachandra]

libc/include/assert.h.def

15

What do you think about moving %%public_api outside of the header guards?
Leave the __assert_fail definition within the header guards but define static_assert with an undef like:

#ifndef __cplusplus
#undef static_assert
#define static_assert _Static_assert
#endif

Then, we don't have to put the assert macro definition in the .h.def file?

[abrachet]

Put %%public_api() outside of include guards and put assert's definition in config/linux.api.td.
Close standard error in assert death test so it doesn't print error message.

libc/config/linux/api.td

 
 def OffT : TypeDecl<"off_t"> {
   let Decl = [{
     #define __need_off_t
     #include <__posix-types.h>
   }];
 }
 
+def AssertMacro : MacroDef<"assert"> {
+  let Defn = [{
+    #undef assert
+
+    #ifdef NDEBUG
+    #define assert(e) (void)0
+    #else
+
+    #ifdef __cplusplus
+    extern "C"
+    #endif
+    _Noreturn void __assert_fail(const char *, const char *, unsigned, const char *);
+
+    #define assert(e)  \
+      ((e) ? (void)0 : __assert_fail(#e, __FILE__, __LINE__, __PRETTY_FUNCTION__))
+
+    #endif
+  }];
+}
+
+def StaticAssertMacro : MacroDef<"static_assert"> {
+  let Defn = [{
+    #ifndef __cplusplus
+    #undef static_assert
+    #define static_assert _Static_assert
+    #endif
+  }];
+}
+
 def NullMacro : MacroDef<"NULL"> {
   let Defn = [{
     #define __need_NULL
     #include <stddef.h>
   }];
 }
 
 def ErrnoMacro : MacroDef<"errno"> {
   let Defn = [{
     #ifdef __cplusplus
     extern "C"
     #endif
     int *__errno_location();
     #define errno (*__errno_location())
   }];
 }
 
+def AssertAPI : PublicAPI<"assert.h"> {
+  let Macros = [
+    AssertMacro,
+    StaticAssertMacro,
+  ];
+}
+
 def MathAPI : PublicAPI<"math.h"> {
   let Functions = [
    "acos",
    "acosl",
   ];
 }
 
 def StringAPI : PublicAPI<"string.h"> {

libc/include/CMakeLists.txt

add_header(
   math_h
   HDR
     math.h
   DEPENDS
     llvm_libc_common_h
 )
 
 add_gen_header(
+  assert_h
+  DEF_FILE assert.h.def
+  GEN_HDR assert.h
+  DEPENDS
+    llvm_libc_common_h
+)
+
+add_gen_header(
   string_h
   DEF_FILE string.h.def
   GEN_HDR string.h
   DEPENDS
     llvm_libc_common_h
 )
 
 add_gen_header(

libc/include/assert.h.def

+//===---------------- C standard library header assert.h ------------------===//
+//
+// 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 <__llvm-libc-common.h>
+
+// This file may be usefully included multiple times to change assert()'s
+// definition based on NDEBUG.
+
+%%public_api()

libc/lib/CMakeLists.txt

 
 add_entrypoint_library(
   llvmlibc
   DEPENDS
+    # assert.h entrypoints
+    __assert_fail
+
     # errno.h entrypoints
     __errno_location
 
     # string.h entrypoints
     strcpy
     strcat
 
     # sys/mman.h entrypoints

libc/spec/stdc.td

def StdC : StandardSpec<"stdc"> {
   NamedType MtxTType = NamedType<"mtx_t">;
   PtrType MtxTTypePtr = PtrType<MtxTType>;
   NamedType ThrdStartTType = NamedType<"thrd_start_t">;
   NamedType ThrdTType = NamedType<"thrd_t">;
   PtrType ThrdTTypePtr = PtrType<ThrdTType>;
 
   PtrType IntPtr = PtrType<IntType>;
 
+  HeaderSpec Assert = HeaderSpec<
+      "assert.h",
+      [
+          Macro<"static_assert">,
+          Macro<"assert">,
+      ],
+      [], // Types
+      [], // Enumerations
+      []
+  >;
+
   HeaderSpec String = HeaderSpec<
       "string.h",
       [
           Macro<"NULL">,
       ],
       [
           SizeTType,
       ],
HeaderSpec Threads = HeaderSpec<
                   ArgSpec<ThrdTTypePtr>,
                   ArgSpec<IntPtr>,
               ]
           >
       ]
   >;
 
   let Headers = [
+    Assert,
     Errno,
     Math,
     String,
     StdIO,
     StdLib,
     Signal,
     Threads,
   ];
 }

libc/src/CMakeLists.txt

+add_subdirectory(assert)
 add_subdirectory(errno)
 add_subdirectory(math)
 add_subdirectory(signal)
 add_subdirectory(stdlib)
 add_subdirectory(string)
 # TODO: Add this target conditional to the target OS.
 add_subdirectory(sys)
 add_subdirectory(threads)
 
 add_subdirectory(__support)

libc/src/assert/CMakeLists.txt

+add_entrypoint_object(
+  __assert_fail
+  SRCS
+    __assert_fail.cpp
+  HDRS
+    assert.h
+  DEPENDS
+    abort
+    # These two dependencies are temporary and should be replaced by fprintf
+    # later.
+    sys_syscall_h
+    linux_syscall_h
+)

libc/src/assert/__assert_fail.cpp

+//===----------------- Implementation of __assert_fail --------------------===//
+//
+// 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/assert/assert.h"
+#include "src/stdlib/abort.h"
+
+// These includes are temporary.
+#include "config/linux/syscall.h" // For internal syscall function.
+#include "include/sys/syscall.h"  // For syscall numbers.
+
+namespace __llvm_libc {
+
+// This is just a temporary solution to make assert available to internal
+// llvm libc code. In the future writeToStderr will not exist and __assert_fail
+// will call fprintf(stderr, ...).
+static void writeToStderr(const char *s) {
+  size_t length = 0;
+  for (const char *curr = s; *curr; ++curr, ++length);
+  __llvm_libc::syscall(SYS_write, 2, s, length);
+}
+
+void LLVM_LIBC_ENTRYPOINT(__assert_fail)(const char *assertion, const char *file,
+                                         unsigned line, const char *function) {
+  writeToStderr(file);
+  writeToStderr(": Assertion failed: '");
+  writeToStderr(assertion);
+  writeToStderr("' in function: '");
+  writeToStderr(function);
+  writeToStderr("'\n");
+  __llvm_libc::abort();
+}
+
+} // namespace __llvm_libc

libc/src/assert/assert.h

+//===-------------------- Internal header for assert ----------*- C++ -*---===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_ASSERT_ASSERT_H
+#define LLVM_LIBC_SRC_ASSERT_ASSERT_H
+
+#include <stddef.h>
+
+namespace __llvm_libc {
+
+[[noreturn]] void __assert_fail(const char *assertion, const char *file, unsigned line,
+                  const char *function);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_ASSERT_ASSERT_H
+
+#undef assert
+
+#ifdef NDEBUG
+#define assert(e) (void)0
+#else
+#define assert(e)                                                              \
+  ((e) ? (void)0 :                                                             \
+    __llvm_libc::__assert_fail(#e, __FILE__, __LINE__, __PRETTY_FUNCTION__))
+#endif

libc/test/src/CMakeLists.txt

+add_subdirectory(assert)
 add_subdirectory(errno)
 add_subdirectory(signal)
 add_subdirectory(stdlib)
 add_subdirectory(string)
 add_subdirectory(sys)
 add_subdirectory(threads)

libc/test/src/assert/CMakeLists.txt

+add_libc_testsuite(libc_assert_unittests)
+
+add_libc_unittest(
+  assert_test
+  SUITE
+    libc_assert_unittests
+  SRCS
+    assert_test.cpp
+  DEPENDS
+    __assert_fail
+    # These are necessary for now because dependencies are not properly added.
+    abort
+    raise
+    _Exit
+)

libc/test/src/assert/assert_test.cpp

+//===---------------------- Unittests for assert --------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#undef NDEBUG
+#include "src/assert/assert.h"
+#include "utils/UnitTest/Test.h"
+
+extern "C" int close(int);
+
+TEST(Assert, Enabled) {
+  // -1 matches against any signal, which is necessary for now until
+  // __llvm_libc::abort() unblocks SIGABRT. Close standard error for the
+  // child process so we don't print the assertion failure message.
+  EXPECT_DEATH(
+      [] {
+        close(2);
+        assert(0);
+      },
+      -1);
+}
+
+#define NDEBUG
+#include "src/assert/assert.h"
+
+TEST(Assert, Disabled) {
+  EXPECT_EXITS([] { assert(0); }, 0);
+}