[libc] Implement `exit` for the GPU partially

[jhuber6]

Summary

This patch implements the exit function on the GPU. This required
breaking the entrypoints calling eachother on linux since this doesn't
work with a non-aliased target. This is only partial support because
full support requires a malloc / free implementation for the exit
callbacks array.

[sivachandra]

libc/src/stdlib/gpu/_Exit.cpp

1

We can unify the _Exit implementation now as it uses the OSUtil abstraction. Move this to the top-level directory and remove the linux/_Exit.cpp implementation.

[jhuber6]

Merging

[sivachandra]

libc/config/gpu/entrypoints.txt

70

Why are they separated out like this?

[jhuber6]

libc/config/gpu/entrypoints.txt

70

It was like that in the x64 one so I just copied it.

[jhuber6]

Fix leftover dep on syscalls.

libc/config/gpu/entrypoints.txt

set(TARGET_LIBC_ENTRYPOINTS
     libc.src.string.strtok
     libc.src.string.strtok_r
 
     # stdlib.h entrypoints
     libc.src.stdlib.atoi
     libc.src.stdlib.atof
     libc.src.stdlib.atol
     libc.src.stdlib.atoll
-    libc.src.stdlib.atexit
     libc.src.stdlib.strtod
     libc.src.stdlib.strtof
     libc.src.stdlib.strtol
     libc.src.stdlib.strtold
     libc.src.stdlib.strtoll
     libc.src.stdlib.strtoul
     libc.src.stdlib.strtoull
 
+    # stdlib.h entrypoints
+    libc.src.stdlib._Exit
+    libc.src.stdlib.atexit
+    libc.src.stdlib.exit
+
     # Only implemented in the test suite
     libc.src.stdlib.malloc
     libc.src.stdlib.aligned_alloc
     libc.src.stdlib.realloc
     libc.src.stdlib.free
 
     # errno.h entrypoints
     libc.src.errno.errno
 )
 
 set(TARGET_LLVMLIBC_ENTRYPOINTS
   ${TARGET_LIBC_ENTRYPOINTS}
 )
 

libc/src/stdlib/CMakeLists.txt

add_entrypoint_object(
   exit
   SRCS
     exit.cpp
   HDRS
     exit.h
   DEPENDS
     ._Exit
     .atexit
+    libc.src.__support.OSUtil.osutil
 )
 
 add_entrypoint_object(
   abort
   ALIAS
   DEPENDS
     .${LIBC_TARGET_OS}.abort
 )

libc/src/stdlib/exit.cpp

 //===-- 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 "src/stdlib/exit.h"
+#include "src/__support/OSUtil/quick_exit.h"
 #include "src/__support/common.h"
-#include "src/stdlib/_Exit.h"
 
 namespace __llvm_libc {
 
 namespace internal {
 void call_exit_callbacks();
 }
 
 LLVM_LIBC_FUNCTION(void, exit, (int status)) {
   internal::call_exit_callbacks();
-  _Exit(status);
+  quick_exit(status);
 }
 
 } // namespace __llvm_libc

libc/src/stdlib/gpu/CMakeLists.txt

+add_entrypoint_object(
+  _Exit
+  SRCS
+    _Exit.cpp
+  HDRS
+    ../_Exit.h
+  DEPENDS
+    libc.include.stdlib
+    libc.src.__support.OSUtil.osutil
+)

libc/src/stdlib/gpu/_Exit.cpp

-//===-- Implementation of exit --------------------------------------------===//
+//===------------------- GPU 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 "src/stdlib/exit.h"
+#include "src/__support/OSUtil/quick_exit.h"
 #include "src/__support/common.h"
+
 #include "src/stdlib/_Exit.h"
 
 namespace __llvm_libc {
 
-namespace internal {
-void call_exit_callbacks();
-}
-
-LLVM_LIBC_FUNCTION(void, exit, (int status)) {
-  internal::call_exit_callbacks();
-  _Exit(status);
-}
+LLVM_LIBC_FUNCTION(void, _Exit, (int status)) { quick_exit(status); }
 
 } // namespace __llvm_libc

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 "include/sys/syscall.h"          // For syscall numbers.
-#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/OSUtil/quick_exit.h"
 #include "src/__support/common.h"
 
 #include "src/stdlib/_Exit.h"
 
 namespace __llvm_libc {
 
-LLVM_LIBC_FUNCTION(void, _Exit, (int status)) {
-  for (;;) {
-    __llvm_libc::syscall_impl(SYS_exit_group, status);
-    __llvm_libc::syscall_impl(SYS_exit, status);
-  }
-}
+LLVM_LIBC_FUNCTION(void, _Exit, (int status)) { quick_exit(status); }
 
 } // namespace __llvm_libc