[libc] Create abort and _Exit

[abrachet]

Summary

This revision creates abort and _Exit implementations

[abrachet]

There are no tests at the moment, although I have tested them. I am waiting for D74665 (which I am waiting for D74652 to hopeful reuse some code), but didn't want this patch to block on these. I'd be happy to rebase against D74665 and add tests here though.

libc/spec/stdc.td

186–187

These should both be _Noreturn or __attribute__((noreturn)) I'm not sure how best to express this. Should I add a noreturn macro to include/__llvm_libc_common.h? Then how would I express this in stdc.td?

[MaskRay]

libc/src/stdlib/abort.cpp

20

If there is a signal handler for SIGABRT, the code should try blocking the signal. Since signals are not available, this is fine.

libc/src/stdlib/linux/_Exit.cpp

20

Which arch does not define SYS_exit_group?

[abrachet]

Remove #ifdef for exit_group.
Add todo to ignore SIGABRT before raise.

[abrachet]

libc/src/stdlib/abort.cpp

20

I have added the above TODO. Maybe it is wrong as I think more about it though, maybe sigprocmask is a better choice to remove the signal handler.

I think there also needs to be some kind of lock once we start playing with signal handlers. WDYT?

libc/src/stdlib/linux/_Exit.cpp

20

It is since 2.5.35. I guess that is old enough to remove the check, so I have removed it.

[abrachet]

Rebase against D74665 to provide tests for this patch.

[sivachandra]

libc/spec/stdc.td

186–187

Will this help: https://reviews.llvm.org/D75393

libc/src/stdlib/abort.cpp

20

Yeah. Please add a big TODO comment explaining what you intend to do in follow-up patches. To get it right, I agree with you that we will need a lock (or multiple locks). So, once the mutex patch lands, we can get back to finishing this.

[abrachet]

• Added more descriptive TODO to abort
• Added forgotten entry points in lib/CMakeLists.txt
• Added changes from D75393
• Rebased against d1536673c68d

[sivachandra]

Just a few comments on comments. But, overall LGTM.

libc/src/stdlib/abort.cpp

19

Do you need sigaction also?

20

I think you mean SIG_DFL?

22

I am being pedantic but I think it is important to leave a more detailed comment here: I think I understand why we need a recursive mutex, but can you also explicitly detail in the comment why a recursive mutex et al is required.

[abrachet]

Update todo comment for abort

[abrachet]

libc/src/stdlib/abort.cpp

19

Yes to remove the user installed SIGABRT handler.

20

Indeed, good catch

20

Yeah. Please add a big TODO comment explaining what you intend to do in follow-up patches. To get it right, I agree with you that we will need a lock (or multiple locks). So, once the mutex patch lands, we can get back to finishing this.

I have added what I think I will do in the future but the more I think about this the more complicated it is. The future patches here should be interesting :)

libc/config/linux/api.td

let TypeDeclarations = [
     SizeT,
   ];
 
   let Functions = [
     "snprintf",
   ];
 }
 
+def StdlibAPI : PublicAPI<"stdlib.h"> {
+  let Functions = [
+    "_Exit",
+    "abort",
+  ];
+}
+
 def ErrnoAPI : PublicAPI<"errno.h"> {
   let Macros = [
     ErrnoMacro,
     // We largely depend on linux/errno.h to give us the
     // various error macro definitions. However, some libc
     // implementations have chosen to provide definitions
     // for some of the error macros to account for the ones
     // missing in linux/errno.h. There is no harm in doing

libc/include/CMakeLists.txt

add_gen_header(
   DEF_FILE signal.h.def
   PARAMS
     platform_signal=../config/${LIBC_TARGET_OS}/signal.h.in
   GEN_HDR signal.h
   DATA_FILES
     ../config/${LIBC_TARGET_OS}/signal.h.in
 )
 
+add_gen_header(
+  stdlib_h
+  DEF_FILE stdlib.h.def
+  GEN_HDR stdlib.h
+  DEPENDS
+    llvm_libc_common_h
+)
+
 # TODO: Not all platforms will have a include/sys directory. Add the sys
 # directory and the targets for sys/*.h files conditional to the OS requiring
 # them.
 file(MAKE_DIRECTORY "sys")
 
 add_gen_header(
   sys_mman_h
   DEF_FILE sys/mman.h.def

libc/include/__llvm-libc-common.h

 #ifdef __cplusplus
 
 #undef __BEGIN_C_DECLS
 #define __BEGIN_C_DECLS extern "C" {
 
 #undef __END_C_DECLS
 #define __END_C_DECLS }
 
+#undef _Noreturn
+#define _Noreturn [[noreturn]]
+
 #else // not __cplusplus
 
 #undef __BEGIN_C_DECLS
 #define __BEGIN_C_DECLS
 
 #undef __END_C_DECLS
 #define __END_C_DECLS
 
 #undef __restrict
 #define __restrict restrict // C99 and above support the restrict keyword.
 
 #endif // __cplusplus
 
 #endif // LLVM_LIBC___COMMON_H

libc/include/stdlib.h.def

+//===---------------- C standard library header stdlib.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_STDLIB_H
+#define LLVM_LIBC_STDLIB_H
+
+#include <__llvm-libc-common.h>
+
+%%public_api()
+
+#endif // LLVM_LIBC_STDLIB_H

libc/lib/CMakeLists.txt

DEPENDS
     mmap
     munmap
 
     # signal.h entrypoints
     raise
     sigaddset
     sigemptyset
     sigprocmask
+
+    # stdlib.h entrypoints
+    _Exit
+    abort
 )
 
 add_entrypoint_library(
   llvmlibm
   DEPENDS
     # math.h entrypoints
     round
 )
 
 add_redirector_library(
   llvmlibc_redirectors
   DEPENDS
     round_redirector
 )

libc/spec/spec.td

 def DoubleType : NamedType<"double">;
 def LongDoubleType : NamedType<"long double">;
 def CharType : NamedType<"char">;
 
 // Common types
 def VoidPtr : PtrType<VoidType>;
 def SizeTType : NamedType<"size_t">;
 
+// _Noreturn is really not a type, but it is convenient to treat it as a type.
+def NoReturn : NamedType<"_Noreturn void">;
+
 class Macro<string name> {
   string Name = name;
 }
 
 class EnumeratedNameValue<string name, string value = "__default__"> {
   string Name = name;
   string Value = value;
 }

libc/spec/stdc.td

HeaderSpec StdIO = HeaderSpec<
               [ArgSpec<CharPtr>,
                ArgSpec<SizeTType>,
                ArgSpec<ConstCharRestrictedPtr>,
                ArgSpec<VarArgType>]
           >,
       ]
   >;
 
+  HeaderSpec StdLib = HeaderSpec<
+      "stdlib.h",
+      [], // Macros
+      [], // Types
+      [], // Enumerations
+      [
+          FunctionSpec<"abort", RetValSpec<NoReturn>, [ArgSpec<VoidType>]>,
+          FunctionSpec<"_Exit", RetValSpec<NoReturn>, [ArgSpec<IntType>]>,
+      ]
+  >;
+
   HeaderSpec Errno = HeaderSpec<
       "errno.h",
       [
         Macro<"errno">,
         Macro<"EDOM">,
         Macro<"EILSEQ">,
         Macro<"ERANGE">,
       ]
HeaderSpec Threads = HeaderSpec<
       ]
   >;
 
   let Headers = [
     Errno,
     Math,
     String,
     StdIO,
+    StdLib,
     Signal,
     Threads,
   ];
 }

libc/src/CMakeLists.txt

 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(__support)

libc/src/stdlib/CMakeLists.txt

+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${LIBC_TARGET_OS})
+endif()
+
+add_entrypoint_object(
+  abort
+  SRCS
+    abort.cpp
+  HDRS
+    abort.h
+  DEPENDS
+    raise
+    _Exit
+    stdlib_h
+)

libc/src/stdlib/_Exit.h

+//===----------------- Implementation header for _Exit ---------*- 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__EXIT_H
+#define LLVM_LIBC_SRC__EXIT_H
+
+namespace __llvm_libc {
+
+[[noreturn]] void _Exit(int status);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC__EXIT_H

libc/src/stdlib/abort.h

+//===----------------- Implementation header for abort ---------*- 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_ABORT_H
+#define LLVM_LIBC_SRC_ABORT_H
+
+namespace __llvm_libc {
+
+[[noreturn]] void abort();
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_ABORT_H

libc/src/stdlib/abort.cpp

+//===---------------------- Implementation of abort -----------------------===//
+//
+// 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/common.h"
+#include "src/signal/raise.h"
+#include "src/stdlib/_Exit.h"
+
+#include "src/stdlib/abort.h"
+
+namespace __llvm_libc {
+
+void LLVM_LIBC_ENTRYPOINT(abort)() {
+  // TODO: When sigprocmask and sigaction land:
+  // Unblock SIGABRT, raise it, if it was ignored or the handler returned,
+  // change its action to SIG_DFL, raise it again.
+  // TODO: When C11 mutexes land:
+  // Aquire recursive mutex (in case the current signal handler for SIGABRT
+  // itself calls abort we don't want to deadlock on the same thread trying
+  // to aquire it's own mutex.)
+  __llvm_libc::raise(SIGABRT);
+  __llvm_libc::raise(SIGKILL);
+  __llvm_libc::_Exit(127);
+}
+
+} // namespace __llvm_libc

libc/src/stdlib/linux/CMakeLists.txt

+add_entrypoint_object(
+  _Exit
+  SRCS
+    _Exit.cpp
+  HDRS
+    ../_Exit.h
+  DEPENDS
+    sys_syscall_h
+    linux_syscall_h
+    stdlib_h
+)

libc/src/stdlib/linux/_Exit.cpp

+//===------------------- Linux Implementation of _Exit --------------------===//
+//
+// 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 "config/linux/syscall.h" // For internal syscall function.
+#include "include/sys/syscall.h"  // For syscall numbers.
+#include "src/__support/common.h"
+
+#include "src/stdlib/_Exit.h"
+
+namespace __llvm_libc {
+
+void LLVM_LIBC_ENTRYPOINT(_Exit)(int status) {
+  for (;;) {
+    __llvm_libc::syscall(SYS_exit_group, status);
+    __llvm_libc::syscall(SYS_exit, status);
+  }
+}
+
+} // namespace __llvm_libc

libc/test/src/CMakeLists.txt

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

libc/test/src/stdlib/CMakeLists.txt

+add_libc_testsuite(libc_stdlib_unittests)
+
+add_libc_unittest(
+  _Exit_test
+  SUITE
+    libc_stdlib_unittests
+  SRCS
+    _Exit_test.cpp
+  DEPENDS
+    stdlib_h
+    _Exit
+)
+
+add_libc_unittest(
+  abort_test
+  SUITE
+    libc_stdlib_unittests
+  SRCS
+    abort_test.cpp
+  DEPENDS
+    stdlib_h
+    signal_h
+    abort
+    _Exit
+    raise
+)

libc/test/src/stdlib/_Exit_test.cpp

+//===----------------------- Unittests for _Exit --------------------------===//
+//
+// 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 "include/stdlib.h"
+#include "src/stdlib/_Exit.h"
+#include "utils/UnitTest/Test.h"
+
+TEST(Stdlib, _Exit) {
+  EXPECT_EXITS([] { __llvm_libc::_Exit(1); }, 1);
+  EXPECT_EXITS([] { __llvm_libc::_Exit(65); }, 65);
+}

libc/test/src/stdlib/abort_test.cpp

+//===----------------------- Unittests for abort --------------------------===//
+//
+// 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 "include/signal.h"
+#include "include/stdlib.h"
+#include "src/stdlib/abort.h"
+#include "utils/UnitTest/Test.h"
+
+TEST(Stdlib, abort) {
+  // -1 matches against any signal, which is necessary for now until
+  // __llvm_libc::abort() unblocks SIGABRT.
+  EXPECT_DEATH([] { __llvm_libc::abort(); }, -1);
+}