[libc] Fix callback type in exit_handlers.cpp not matching

[jhuber6]

Summary:
This file is an object library, but uses the LIBC_COPT_PUBLIC_PACKAING
option. This will always be undefined which leads to a type mismatch
when uses actually try to link against it. This patch simply removes
this and turns it into a header only library. This means that the
implementations of the callback lists and the mutexes need to live in
their respective files. The result is that atexit needs to be defined
for at_quick_exit to be valid.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Joseph Huber (jhuber6)

Changes

Summary:
This file is an object library, but uses the LIBC_COPT_PUBLIC_PACKAING
option. This will always be undefined which leads to a type mismatch
when uses actually try to link against it. This patch simply removes
this and turns it into a header only library. This means that the
implementations of the callback lists and the mutexes need to live in
their respective files. The result is that atexit needs to be defined
for at_quick_exit to be valid.

---

Full diff: https://github.com/llvm/llvm-project/pull/97642.diff

5 Files Affected:

• (modified) libc/src/stdlib/CMakeLists.txt (+6-6)
• (modified) libc/src/stdlib/at_quick_exit.cpp (+2)
• (modified) libc/src/stdlib/atexit.cpp (+3)
• (removed) libc/src/stdlib/exit_handler.cpp (-42)
• (modified) libc/src/stdlib/exit_handler.h (+21-3)

diff --git a/libc/src/stdlib/CMakeLists.txt b/libc/src/stdlib/CMakeLists.txt
index 677bf358c82c4..3913db7938fdd 100644
--- a/libc/src/stdlib/CMakeLists.txt
+++ b/libc/src/stdlib/CMakeLists.txt
@@ -458,15 +458,11 @@ add_entrypoint_object(
 
 # TODO: Move all exit functions to linux specific 
 
-if (TARGET libc.src.__support.threads.mutex)
-add_object_library(
+if(TARGET libc.src.__support.threads.mutex)
+add_header_library(
   exit_handler
-  SRCS
-    exit_handler.cpp
   HDRS
     exit_handler.h
-  CXX_STANDARD
-    20 # For constinit 
   DEPENDS
     libc.src.__support.CPP.mutex
     libc.src.__support.CPP.new
@@ -483,6 +479,8 @@ add_entrypoint_object(
     atexit.cpp
   HDRS
     atexit.h
+  CXX_STANDARD
+    20 # For constinit 
   DEPENDS
     .exit_handler
 )
@@ -493,6 +491,8 @@ add_entrypoint_object(
     at_quick_exit.cpp
   HDRS
     at_quick_exit.h
+  CXX_STANDARD
+    20 # For constinit 
   DEPENDS
     .exit_handler
 )
diff --git a/libc/src/stdlib/at_quick_exit.cpp b/libc/src/stdlib/at_quick_exit.cpp
index 752d67e7fe44d..ada845633c825 100644
--- a/libc/src/stdlib/at_quick_exit.cpp
+++ b/libc/src/stdlib/at_quick_exit.cpp
@@ -13,6 +13,8 @@
 
 namespace LIBC_NAMESPACE {
 
+constinit ExitCallbackList at_quick_exit_callbacks;
+
 LLVM_LIBC_FUNCTION(int, at_quick_exit, (__atexithandler_t callback)) {
   return add_atexit_unit(
       at_quick_exit_callbacks,
diff --git a/libc/src/stdlib/atexit.cpp b/libc/src/stdlib/atexit.cpp
index ca3cbfe87a88c..fabe6524903f9 100644
--- a/libc/src/stdlib/atexit.cpp
+++ b/libc/src/stdlib/atexit.cpp
@@ -13,6 +13,9 @@
 
 namespace LIBC_NAMESPACE {
 
+constinit ExitCallbackList atexit_callbacks;
+Mutex handler_list_mtx(false, false, false, false);
+
 extern "C" {
 
 int __cxa_atexit(AtExitCallback *callback, void *payload, void *) {
diff --git a/libc/src/stdlib/exit_handler.cpp b/libc/src/stdlib/exit_handler.cpp
deleted file mode 100644
index ed41247e4a31d..0000000000000
--- a/libc/src/stdlib/exit_handler.cpp
+++ /dev/null
@@ -1,42 +0,0 @@
-//===--- Implementation of exit_handler------------------------------------===//
-//
-// 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_handler.h"
-#include "src/__support/CPP/mutex.h" // lock_guard
-
-namespace LIBC_NAMESPACE {
-
-constinit ExitCallbackList at_quick_exit_callbacks;
-constinit ExitCallbackList atexit_callbacks;
-
-Mutex handler_list_mtx(false, false, false, false);
-
-void stdc_at_exit_func(void *payload) {
-  reinterpret_cast<StdCAtExitCallback *>(payload)();
-}
-
-void call_exit_callbacks(ExitCallbackList &callbacks) {
-  handler_list_mtx.lock();
-  while (!callbacks.empty()) {
-    AtExitUnit &unit = callbacks.back();
-    callbacks.pop_back();
-    handler_list_mtx.unlock();
-    unit.callback(unit.payload);
-    handler_list_mtx.lock();
-  }
-  ExitCallbackList::destroy(&callbacks);
-}
-
-int add_atexit_unit(ExitCallbackList &callbacks, const AtExitUnit &unit) {
-  cpp::lock_guard lock(handler_list_mtx);
-  if (callbacks.push_back(unit))
-    return 0;
-  return -1;
-}
-
-} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdlib/exit_handler.h b/libc/src/stdlib/exit_handler.h
index 8494c2f2e526e..97657cf5b3fd6 100644
--- a/libc/src/stdlib/exit_handler.h
+++ b/libc/src/stdlib/exit_handler.h
@@ -42,11 +42,29 @@ extern ExitCallbackList at_quick_exit_callbacks;
 
 extern Mutex handler_list_mtx;
 
-void stdc_at_exit_func(void *payload);
+LIBC_INLINE void stdc_at_exit_func(void *payload) {
+  reinterpret_cast<StdCAtExitCallback *>(payload)();
+}
 
-void call_exit_callbacks(ExitCallbackList &callbacks);
+LIBC_INLINE void call_exit_callbacks(ExitCallbackList &callbacks) {
+  handler_list_mtx.lock();
+  while (!callbacks.empty()) {
+    AtExitUnit &unit = callbacks.back();
+    callbacks.pop_back();
+    handler_list_mtx.unlock();
+    unit.callback(unit.payload);
+    handler_list_mtx.lock();
+  }
+  ExitCallbackList::destroy(&callbacks);
+}
 
-int add_atexit_unit(ExitCallbackList &callbacks, const AtExitUnit &unit);
+LIBC_INLINE int add_atexit_unit(ExitCallbackList &callbacks,
+                                const AtExitUnit &unit) {
+  cpp::lock_guard lock(handler_list_mtx);
+  if (callbacks.push_back(unit))
+    return 0;
+  return -1;
+}
 
 } // namespace LIBC_NAMESPACE