[libc][OSUtil] refactor quick_exit to be an object library everywhere (#85955)

The usage of __builtin_unreachable after calls to quick_exit were distressing.
If a function is properly marked [[noreturn]] then __builtin_unreachable is not
necessary.

Looking into this further, we seem to have header only implementations for CPU
targets. The inline nature of these functions is curious; we're going to exit,
it doesn't matter if we need to pay the call of a function or not. If we just
make these functions have distinct TUs rather than be header only, we can clean
up the cmake rules for quick_exit which were different between CPU and GPU.

Remove darwin support for quick_exit. This isn't being tested, and we can bring
it back when necessary.

Author: nickdesaulniers

libc/src/__support/OSUtil/CMakeLists.txt

@@ -8,23 +8,10 @@ if(NOT TARGET ${target_os_util})
   return()
 endif()
 
-# The OSUtil is an object library in GPU mode.
-if(NOT LIBC_TARGET_OS_IS_GPU)
-  add_header_library(
-    osutil
-    HDRS
-      io.h
-      quick_exit.h
-      syscall.h
-    DEPENDS
-      ${target_os_util}
-  )
-else()
-  add_object_library(
-    osutil
-    ALIAS
-      ${target_os_util}
-    DEPENDS
-      ${target_os_util}
-  )
-endif()
+add_object_library(
+  osutil
+  ALIAS
+    ${target_os_util}
+  DEPENDS
+    ${target_os_util}
+)

libc/src/__support/OSUtil/baremetal/CMakeLists.txt

@@ -1,8 +1,9 @@
-add_header_library(
+add_object_library(
   baremetal_util
+  SRCS
+    quick_exit.cpp
   HDRS
     io.h
-    quick_exit.h
   DEPENDS
     libc.src.__support.common
     libc.src.__support.CPP.string_view

libc/src/__support/OSUtil/baremetal/quick_exit.h renamed to libc/src/__support/OSUtil/baremetal/quick_exit.cpp

@@ -6,16 +6,13 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_BAREMETAL_QUICK_EXIT_H
-#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_BAREMETAL_QUICK_EXIT_H
-
-namespace LIBC_NAMESPACE {
+#include "src/__support/OSUtil/quick_exit.h"
 
 // This is intended to be provided by the vendor.
-extern "C" void __llvm_libc_quick_exit(int status);
+[[noreturn]] extern "C" void __llvm_libc_quick_exit(int status);
 
-void quick_exit(int status) { __llvm_libc_quick_exit(status); }
+namespace LIBC_NAMESPACE {
 
-} // namespace LIBC_NAMESPACE
+[[noreturn]] void quick_exit(int status) { __llvm_libc_quick_exit(status); }
 
-#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_BAREMETAL_QUICK_EXIT_H
+} // namespace LIBC_NAMESPACE

libc/src/__support/OSUtil/darwin/CMakeLists.txt

@@ -8,7 +8,6 @@ add_header_library(
   darwin_util
   HDRS
     io.h
-    quick_exit.h
     syscall.h
   DEPENDS
     .${LIBC_TARGET_ARCHITECTURE}.darwin_util

libc/src/__support/OSUtil/darwin/quick_exit.h

@@ -4,7 +4,6 @@ add_object_library(
     quick_exit.cpp
     io.cpp
   HDRS
-    quick_exit.h
     io.h
   DEPENDS
     libc.src.__support.common

libc/src/__support/OSUtil/gpu/CMakeLists.txt

@@ -6,17 +6,14 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_GPU_QUICK_EXIT_H
-#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_GPU_QUICK_EXIT_H
-
-#include "quick_exit.h"
+#include "src/__support/OSUtil/quick_exit.h"
 
 #include "src/__support/RPC/rpc_client.h"
 #include "src/__support/macros/properties/architectures.h"
 
 namespace LIBC_NAMESPACE {
 
-void quick_exit(int status) {
+[[noreturn]] void quick_exit(int status) {
   // We want to first make sure the server is listening before we exit.
   rpc::Client::Port port = rpc::client.open<RPC_EXIT>();
   port.send_and_recv([](rpc::Buffer *) {}, [](rpc::Buffer *) {});
@@ -29,5 +26,3 @@ void quick_exit(int status) {
 }
 
 } // namespace LIBC_NAMESPACE
-
-#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_GPU_QUICK_EXIT_H

libc/src/__support/OSUtil/gpu/quick_exit.cpp

@@ -4,11 +4,12 @@ endif()
 
 add_subdirectory(${LIBC_TARGET_ARCHITECTURE})
 
-add_header_library(
+add_object_library(
   linux_util
+  SRCS
+    quick_exit.cpp
   HDRS
     io.h
-    quick_exit.h
     syscall.h
   DEPENDS
     .${LIBC_TARGET_ARCHITECTURE}.linux_${LIBC_TARGET_ARCHITECTURE}_util

libc/src/__support/OSUtil/gpu/quick_exit.h

@@ -6,13 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_QUICK_EXIT_H
-#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_QUICK_EXIT_H
-
-#include "syscall.h" // For internal syscall function.
-
 #include "src/__support/common.h"
-
+#include "syscall.h"     // For internal syscall function.
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace LIBC_NAMESPACE {
@@ -22,7 +17,7 @@ namespace LIBC_NAMESPACE {
 #ifdef LIBC_TARGET_ARCH_IS_X86
 __attribute__((no_stack_protector))
 #endif
-LIBC_INLINE void
+__attribute__((noreturn)) void
 quick_exit(int status) {
   for (;;) {
     LIBC_NAMESPACE::syscall_impl<long>(SYS_exit_group, status);
@@ -31,5 +26,3 @@ quick_exit(int status) {
 }
 
 } // namespace LIBC_NAMESPACE
-
-#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_LINUX_QUICK_EXIT_H

libc/src/__support/OSUtil/linux/CMakeLists.txt

@@ -9,17 +9,10 @@
 #ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_QUICK_EXIT_H
 #define LLVM_LIBC_SRC___SUPPORT_OSUTIL_QUICK_EXIT_H
 
-#include "src/__support/macros/properties/architectures.h"
+namespace LIBC_NAMESPACE {
 
-#if defined(LIBC_TARGET_ARCH_IS_GPU)
-#include "gpu/quick_exit.h"
-#elif defined(__APPLE__)
-#include "darwin/quick_exit.h"
-#elif defined(__linux__)
-#include "linux/quick_exit.h"
-#elif defined(__ELF__)
-// TODO: Ideally we would have LIBC_TARGET_OS_IS_BAREMETAL.
-#include "baremetal/quick_exit.h"
-#endif
+[[noreturn]] void quick_exit(int status);
+
+}
 
 #endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_QUICK_EXIT_H

libc/src/__support/OSUtil/linux/quick_exit.h renamed to libc/src/__support/OSUtil/linux/quick_exit.cpp

@@ -414,10 +414,11 @@ add_entrypoint_object(
   CXX_STANDARD
     20 # For constinit of the atexit callback list.
   DEPENDS
-    libc.src.__support.fixedvector
+    libc.src.__support.CPP.new
+    libc.src.__support.OSUtil.osutil
     libc.src.__support.blockstore
+    libc.src.__support.fixedvector
     libc.src.__support.threads.mutex
-    libc.src.__support.CPP.new
 )
 
 add_entrypoint_object(

libc/src/__support/OSUtil/quick_exit.h

@@ -13,9 +13,8 @@
 
 namespace LIBC_NAMESPACE {
 
-LLVM_LIBC_FUNCTION(void, _Exit, (int status)) {
+[[noreturn]] LLVM_LIBC_FUNCTION(void, _Exit, (int status)) {
   quick_exit(status);
-  __builtin_unreachable();
 }
 
 } // namespace LIBC_NAMESPACE

libc/src/stdlib/CMakeLists.txt

@@ -14,10 +14,9 @@ extern "C" void __cxa_finalize(void *);
 
 namespace LIBC_NAMESPACE {
 
-LLVM_LIBC_FUNCTION(void, exit, (int status)) {
+[[noreturn]] LLVM_LIBC_FUNCTION(void, exit, (int status)) {
   __cxa_finalize(nullptr);
   quick_exit(status);
-  __builtin_unreachable();
 }
 
 } // namespace LIBC_NAMESPACE

libc/src/stdlib/_Exit.cpp

@@ -1002,10 +1002,7 @@ libc_support_library(
 libc_support_library(
     name = "__support_osutil_quick_exit",
     hdrs = ["src/__support/OSUtil/quick_exit.h"],
-    textual_hdrs = [
-        "src/__support/OSUtil/linux/quick_exit.h",
-        #TODO: add support for GPU quick_exit (isn't just in a header.)
-    ],
+    srcs = ["src/__support/OSUtil/linux/quick_exit.cpp"],
     deps = [
         ":__support_osutil_syscall",
     ],