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[libc++abi] Define __cxa_thread_atexit on platforms that need it #186054

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[libc++abi] Define __cxa_thread_atexit on platforms that need it #186054

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46301f0
[libc++abi] Revert gating of `__cxa_thread_atexit` on Wasm/WASI
whitequark Mar 12, 2026
d969738
Merge branch 'main' into wasi-__cxa_thread_atexit
ldionne Aug 3, 2026
c15c52f
Make header consistent with .cpp file
ldionne Aug 3, 2026
edecf53
Move logic to source file, not CMake
ldionne Aug 3, 2026
07bda8b
Opt-out instead of opt-in
ldionne Aug 3, 2026
ab56444
Update header
ldionne Aug 3, 2026
9eb67b3
Use 0-1 macro
ldionne Aug 4, 2026
2d35faa
Merge branch 'main' into wasi-__cxa_thread_atexit
ldionne Aug 4, 2026
ad67746
Disable on Windows too.
ldionne Aug 4, 2026
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11 changes: 11 additions & 0 deletions libcxxabi/include/__cxxabi_config.h
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Original file line number Diff line number Diff line change
Expand Up @@ -134,4 +134,15 @@
# define _LIBCXXABI_DISABLE_POINTER_FIELD_PROTECTION
#endif

// On Apple, Clang generates calls to _tlv_atexit and __cxa_thread_atexit is defined
// in libc instead. AIX uses a different mechanism for registering thread local
// destructors (__pt_atexit_np).
//
// On other platforms, libc++abi provides __cxa_thread_atexit.
#if defined(__APPLE__) || defined(_AIX)
# define _LIBCXXABI_DEFINE_THREAD_ATEXIT 0
#else
# define _LIBCXXABI_DEFINE_THREAD_ATEXIT 1
#endif

#endif // ____CXXABI_CONFIG_H
4 changes: 2 additions & 2 deletions libcxxabi/include/cxxabi.h
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Expand Up @@ -179,8 +179,8 @@ __cxa_decrement_exception_refcount(void *primary_exception) _LIBCXXABI_NOEXCEPT;
extern _LIBCXXABI_FUNC_VIS bool __cxa_uncaught_exception() _LIBCXXABI_NOEXCEPT;
extern _LIBCXXABI_FUNC_VIS unsigned int __cxa_uncaught_exceptions() _LIBCXXABI_NOEXCEPT;

#if defined(__linux__) || defined(__Fuchsia__)
// Linux and Fuchsia TLS support. Not yet an official part of the Itanium ABI.
#if _LIBCXXABI_DEFINE_THREAD_ATEXIT
// Register a thread local destructor. This is not yet an official part of the Itanium ABI.
// https://sourceware.org/glibc/wiki/Destructor%20support%20for%20thread_local%20variables
extern _LIBCXXABI_FUNC_VIS int __cxa_thread_atexit(void (*)(void *), void *,
void *) _LIBCXXABI_NOEXCEPT;
Expand Down
8 changes: 1 addition & 7 deletions libcxxabi/src/CMakeLists.txt
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Expand Up @@ -9,6 +9,7 @@ set(LIBCXXABI_SOURCES
cxa_handlers.cpp
cxa_vector.cpp
cxa_virtual.cpp
cxa_thread_atexit.cpp
# C++ STL files
stdlib_exception.cpp
stdlib_stdexcept.cpp
Expand Down Expand Up @@ -36,13 +37,6 @@ else()
)
endif()

if (LIBCXXABI_ENABLE_THREADS AND (UNIX OR FUCHSIA) AND NOT (APPLE OR CYGWIN)
AND NOT ("${CMAKE_SYSTEM_NAME}" MATCHES "AIX"))
list(APPEND LIBCXXABI_SOURCES
cxa_thread_atexit.cpp
)
endif()

set(LIBCXXABI_HEADERS
../include/cxxabi.h
)
Expand Down
18 changes: 11 additions & 7 deletions libcxxabi/src/cxa_thread_atexit.cpp
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Expand Up @@ -6,16 +6,18 @@
//
//===----------------------------------------------------------------------===//

#include "abort_message.h"
#include "cxxabi.h"

#if !defined(_LIBCXXABI_HAS_NO_THREADS) && _LIBCXXABI_DEFINE_THREAD_ATEXIT

#include <__thread/support.h>
#ifndef _LIBCXXABI_HAS_NO_THREADS
#include <stdlib.h>

#include "abort_message.h"

#if defined(__ELF__) && defined(_LIBCXXABI_LINK_PTHREAD_LIB)
#pragma comment(lib, "pthread")
#endif
#endif

#include <stdlib.h>

namespace __cxxabiv1 {

Expand Down Expand Up @@ -106,7 +108,6 @@ namespace {

#endif // HAVE___CXA_THREAD_ATEXIT_IMPL

#if defined(__linux__) || defined(__Fuchsia__)
extern "C" {
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_LIBCXXABI_FUNC_VIS int __cxa_thread_atexit(Dtor dtor, void* obj, void* dso_symbol) throw() {
Expand Down Expand Up @@ -141,6 +142,9 @@ extern "C" {
}
#endif // HAVE___CXA_THREAD_ATEXIT_IMPL
}

} // extern "C"
#endif // defined(__linux__) || defined(__Fuchsia__)

} // namespace __cxxabiv1

#endif // !defined(_LIBCXXABI_HAS_NO_THREADS) && _LIBCXXABI_DEFINE_THREAD_ATEXIT
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