[libc-commits] [libc] [libc][patch 2/n] provide _malloc_thread_cleanup option (PR #133730)
Schrodinger ZHU Yifan via libc-commits
libc-commits at lists.llvm.org
Mon Mar 31 07:54:45 PDT 2025
https://github.com/SchrodingerZhu created https://github.com/llvm/llvm-project/pull/133730
- **[libc] ensure tls dtors are called in main thread**
- **[libc] add _malloc_thread_cleanup option**
>From 175ae9a1e62fd06977a4646d46aaca1b9fa526e3 Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <i at zhuyi.fan>
Date: Sun, 30 Mar 2025 12:15:40 -0400
Subject: [PATCH 1/2] [libc] ensure tls dtors are called in main thread
---
libc/src/__support/threads/thread.cpp | 5 ++++
libc/src/__support/threads/thread.h | 6 ++--
libc/src/stdlib/exit.cpp | 4 +++
.../src/__support/threads/CMakeLists.txt | 21 +++++++++++++
.../__support/threads/double_exit_test.cpp | 23 ++++++++++++++
.../src/__support/threads/main_exit_test.cpp | 30 +++++++++++++++++++
6 files changed, 87 insertions(+), 2 deletions(-)
create mode 100644 libc/test/integration/src/__support/threads/double_exit_test.cpp
create mode 100644 libc/test/integration/src/__support/threads/main_exit_test.cpp
diff --git a/libc/src/__support/threads/thread.cpp b/libc/src/__support/threads/thread.cpp
index 6f6b75be5766d..c7135596622c6 100644
--- a/libc/src/__support/threads/thread.cpp
+++ b/libc/src/__support/threads/thread.cpp
@@ -154,6 +154,9 @@ ThreadAtExitCallbackMgr *get_thread_atexit_callback_mgr() {
}
void call_atexit_callbacks(ThreadAttributes *attrib) {
+ if (attrib->dtors_called)
+ return;
+ attrib->dtors_called = true;
attrib->atexit_callback_mgr->call();
for (size_t i = 0; i < TSS_KEY_COUNT; ++i) {
TSSValueUnit &unit = tss_values[i];
@@ -163,6 +166,8 @@ void call_atexit_callbacks(ThreadAttributes *attrib) {
}
}
+extern "C" void __cxa_thread_finalize() { call_atexit_callbacks(self.attrib); }
+
} // namespace internal
cpp::optional<unsigned int> new_tss_key(TSSDtor *dtor) {
diff --git a/libc/src/__support/threads/thread.h b/libc/src/__support/threads/thread.h
index f2b1f6bbb253d..f7710fde2c70d 100644
--- a/libc/src/__support/threads/thread.h
+++ b/libc/src/__support/threads/thread.h
@@ -109,12 +109,14 @@ struct alignas(STACK_ALIGNMENT) ThreadAttributes {
ThreadReturnValue retval;
ThreadAtExitCallbackMgr *atexit_callback_mgr;
void *platform_data;
+ bool dtors_called;
- constexpr ThreadAttributes()
+ LIBC_INLINE constexpr ThreadAttributes()
: detach_state(uint32_t(DetachState::DETACHED)), stack(nullptr),
stacksize(0), guardsize(0), tls(0), tls_size(0), owned_stack(false),
tid(-1), style(ThreadStyle::POSIX), retval(),
- atexit_callback_mgr(nullptr), platform_data(nullptr) {}
+ atexit_callback_mgr(nullptr), platform_data(nullptr),
+ dtors_called(false) {}
};
using TSSDtor = void(void *);
diff --git a/libc/src/stdlib/exit.cpp b/libc/src/stdlib/exit.cpp
index 28a6f8a63c0c6..097a52339e5e8 100644
--- a/libc/src/stdlib/exit.cpp
+++ b/libc/src/stdlib/exit.cpp
@@ -14,8 +14,12 @@
namespace LIBC_NAMESPACE_DECL {
extern "C" void __cxa_finalize(void *);
+extern "C" [[gnu::weak]] void __cxa_thread_finalize();
+// TODO: use recursive mutex to protect this routine.
[[noreturn]] LLVM_LIBC_FUNCTION(void, exit, (int status)) {
+ if (__cxa_thread_finalize)
+ __cxa_thread_finalize();
__cxa_finalize(nullptr);
internal::exit(status);
}
diff --git a/libc/test/integration/src/__support/threads/CMakeLists.txt b/libc/test/integration/src/__support/threads/CMakeLists.txt
index 5a12d28ada3fd..40e96681b1207 100644
--- a/libc/test/integration/src/__support/threads/CMakeLists.txt
+++ b/libc/test/integration/src/__support/threads/CMakeLists.txt
@@ -25,3 +25,24 @@ add_integration_test(
DEPENDS
libc.src.__support.threads.thread
)
+
+add_integration_test(
+ main_exit_test
+ SUITE
+ libc-support-threads-integration-tests
+ SRCS
+ main_exit_test.cpp
+ DEPENDS
+ libc.src.__support.threads.thread
+)
+
+add_integration_test(
+ double_exit_test
+ SUITE
+ libc-support-threads-integration-tests
+ SRCS
+ double_exit_test.cpp
+ DEPENDS
+ libc.src.__support.threads.thread
+ libc.src.stdlib.exit
+)
diff --git a/libc/test/integration/src/__support/threads/double_exit_test.cpp b/libc/test/integration/src/__support/threads/double_exit_test.cpp
new file mode 100644
index 0000000000000..e4a163644a970
--- /dev/null
+++ b/libc/test/integration/src/__support/threads/double_exit_test.cpp
@@ -0,0 +1,23 @@
+//===-- Test handling of thread local data --------------------------------===//
+//
+// 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/threads/thread.h"
+#include "src/stdlib/exit.h"
+#include "test/IntegrationTest/test.h"
+
+extern "C" {
+[[gnu::weak]]
+void *__dso_handle = nullptr;
+int __cxa_thread_atexit_impl(void (*func)(void *), void *arg, void *dso);
+}
+
+TEST_MAIN() {
+ __cxa_thread_atexit_impl([](void *) { LIBC_NAMESPACE::exit(0); }, nullptr,
+ __dso_handle);
+ return 0;
+}
diff --git a/libc/test/integration/src/__support/threads/main_exit_test.cpp b/libc/test/integration/src/__support/threads/main_exit_test.cpp
new file mode 100644
index 0000000000000..c90e4e569cfba
--- /dev/null
+++ b/libc/test/integration/src/__support/threads/main_exit_test.cpp
@@ -0,0 +1,30 @@
+//===-- Test handling of thread local data --------------------------------===//
+//
+// 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/threads/thread.h"
+#include "test/IntegrationTest/test.h"
+
+bool called = false;
+
+extern "C" {
+[[gnu::weak]]
+void *__dso_handle = nullptr;
+int __cxa_thread_atexit_impl(void (*func)(void *), void *arg, void *dso);
+}
+
+[[gnu::destructor]]
+void destructor() {
+ if (!called)
+ __builtin_trap();
+}
+
+TEST_MAIN() {
+ __cxa_thread_atexit_impl([](void *) { called = true; }, nullptr,
+ __dso_handle);
+ return 0;
+}
>From d3a4c5e66b1a6de07f991699ff8f39f1dad72921 Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Mon, 31 Mar 2025 10:42:11 -0400
Subject: [PATCH 2/2] [libc] add _malloc_thread_cleanup option
---
libc/config/config.json | 4 ++++
libc/docs/configure.rst | 1 +
libc/src/__support/threads/linux/CMakeLists.txt | 7 +++++++
libc/src/__support/threads/linux/thread.cpp | 9 +++++++++
libc/src/stdlib/CMakeLists.txt | 8 ++++++++
libc/src/stdlib/atexit.cpp | 4 ++++
6 files changed, 33 insertions(+)
diff --git a/libc/config/config.json b/libc/config/config.json
index d738aade74427..b2688f1b29309 100644
--- a/libc/config/config.json
+++ b/libc/config/config.json
@@ -89,6 +89,10 @@
"LIBC_CONF_RWLOCK_DEFAULT_SPIN_COUNT": {
"value": 100,
"doc": "Default number of spins before blocking if a rwlock is in contention (default to 100)."
+ },
+ "LIBC_CONF_ENABLE_MALLOC_THREAD_CLEANUP": {
+ "value": false,
+ "doc": "Enable the `_malloc_thread_cleanup` weak symbol. When defined, this is function is called after `__cxa` and pthread-specific dtors. On main thread, this will be called after `atexit` functions and `.fini` dtors, right before TLS tearing down. This function can be overridden by allocators to perform cleanup. Allocators can use this symbol to avoid registering thread dtors using potentially reentrant routines."
}
},
"math": {
diff --git a/libc/docs/configure.rst b/libc/docs/configure.rst
index dee9a63101eb9..182d373c075f6 100644
--- a/libc/docs/configure.rst
+++ b/libc/docs/configure.rst
@@ -47,6 +47,7 @@ to learn about the defaults for your platform and target.
- ``LIBC_CONF_PRINTF_FLOAT_TO_STR_USE_MEGA_LONG_DOUBLE_TABLE``: Use large table for better printf long double performance.
- ``LIBC_CONF_PRINTF_RUNTIME_DISPATCH``: Use dynamic dispatch for the output mechanism to reduce code size.
* **"pthread" options**
+ - ``LIBC_CONF_ENABLE_MALLOC_THREAD_CLEANUP``: Enable the `_malloc_thread_cleanup` weak symbol. When defined, this is function is called after `__cxa` and pthread-specific dtors. On main thread, this will be called after `atexit` functions and `.fini` dtors, right before TLS tearing down. This function can be overridden by allocators to perform cleanup. Allocators can use this symbol to avoid registering thread dtors using potentially reentrant routines.
- ``LIBC_CONF_RAW_MUTEX_DEFAULT_SPIN_COUNT``: Default number of spins before blocking if a mutex is in contention (default to 100).
- ``LIBC_CONF_RWLOCK_DEFAULT_SPIN_COUNT``: Default number of spins before blocking if a rwlock is in contention (default to 100).
- ``LIBC_CONF_TIMEOUT_ENSURE_MONOTONICITY``: Automatically adjust timeout to CLOCK_MONOTONIC (default to true). POSIX API may require CLOCK_REALTIME, which can be unstable and leading to unexpected behavior. This option will convert the real-time timestamp to monotonic timestamp relative to the time of call.
diff --git a/libc/src/__support/threads/linux/CMakeLists.txt b/libc/src/__support/threads/linux/CMakeLists.txt
index 364e7e2b90585..3e7c16afe0f6e 100644
--- a/libc/src/__support/threads/linux/CMakeLists.txt
+++ b/libc/src/__support/threads/linux/CMakeLists.txt
@@ -71,6 +71,12 @@ add_header_library(
libc.src.__support.threads.mutex_common
)
+if (LIBC_CONF_ENABLE_MALLOC_THREAD_CLEANUP)
+ set(malloc_cleanup_flags -DLIBC_COPT_ENABLE_MALLOC_THREAD_CLEANUP)
+else()
+ set(malloc_cleanup_flags)
+endif()
+
add_object_library(
thread
SRCS
@@ -89,6 +95,7 @@ add_object_library(
libc.src.__support.threads.thread_common
COMPILE_OPTIONS
${libc_opt_high_flag}
+ ${malloc_cleanup_flags}
-fno-omit-frame-pointer # This allows us to sniff out the thread args from
# the new thread's stack reliably.
-Wno-frame-address # Yes, calling __builtin_return_address with a
diff --git a/libc/src/__support/threads/linux/thread.cpp b/libc/src/__support/threads/linux/thread.cpp
index c531d74c53355..2d6d4e517064d 100644
--- a/libc/src/__support/threads/linux/thread.cpp
+++ b/libc/src/__support/threads/linux/thread.cpp
@@ -482,6 +482,10 @@ int Thread::get_name(cpp::StringStream &name) const {
return 0;
}
+#ifdef LIBC_COPT_ENABLE_MALLOC_THREAD_CLEANUP
+extern "C" [[gnu::weak]] void _malloc_thread_cleanup();
+#endif // LIBC_COPT_ENABLE_MALLOC_THREAD_CLEANUP
+
void thread_exit(ThreadReturnValue retval, ThreadStyle style) {
auto attrib = self.attrib;
@@ -494,6 +498,11 @@ void thread_exit(ThreadReturnValue retval, ThreadStyle style) {
// different thread. The destructors of thread local and TSS objects should
// be called by the thread which owns them.
internal::call_atexit_callbacks(attrib);
+#ifdef LIBC_COPT_ENABLE_MALLOC_THREAD_CLEANUP
+ // call _malloc_thread_cleanup after the atexit callbacks
+ if (_malloc_thread_cleanup)
+ _malloc_thread_cleanup();
+#endif // LIBC_COPT_ENABLE_MALLOC_THREAD_CLEANUP
uint32_t joinable_state = uint32_t(DetachState::JOINABLE);
if (!attrib->detach_state.compare_exchange_strong(
diff --git a/libc/src/stdlib/CMakeLists.txt b/libc/src/stdlib/CMakeLists.txt
index 74ae864f72e23..7dd0c969cf9b2 100644
--- a/libc/src/stdlib/CMakeLists.txt
+++ b/libc/src/stdlib/CMakeLists.txt
@@ -589,6 +589,12 @@ add_header_library(
)
endif()
+if (LIBC_CONF_ENABLE_MALLOC_THREAD_CLEANUP)
+ set(malloc_cleanup_flags -DLIBC_COPT_ENABLE_MALLOC_THREAD_CLEANUP)
+else()
+ set(malloc_cleanup_flags)
+endif()
+
add_entrypoint_object(
atexit
SRCS
@@ -599,6 +605,8 @@ add_entrypoint_object(
20 # For constinit
DEPENDS
.exit_handler
+ COMPILE_OPTIONS
+ ${malloc_cleanup_flags}
)
add_entrypoint_object(
diff --git a/libc/src/stdlib/atexit.cpp b/libc/src/stdlib/atexit.cpp
index 799aad136bda5..979ed1f29b642 100644
--- a/libc/src/stdlib/atexit.cpp
+++ b/libc/src/stdlib/atexit.cpp
@@ -18,6 +18,10 @@ constinit ExitCallbackList atexit_callbacks;
Mutex handler_list_mtx(false, false, false, false);
[[gnu::weak]] extern void teardown_main_tls();
+namespace internal {
+[[gnu::weak]] extern void call_atexit_callbacks();
+}
+
extern "C" {
int __cxa_atexit(AtExitCallback *callback, void *payload, void *) {
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