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__builtin_thread_pointers now returns non-null even in single threaded builds #26751

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__builtin_thread_pointers now returns non-null even in single threaded builds #26751

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2 changes: 2 additions & 0 deletions test/other/test_pthread_stub.c
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Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,8 @@ void test_pthreads() {
int rtn;
int res;

printf("__builtin_thread_pointer non-null: %d\n", __builtin_thread_pointer() != NULL);

// pthread_atfork should silently succeed.
CHECK_SUCCESS(pthread_atfork(NULL, NULL, NULL));

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1 change: 1 addition & 0 deletions test/other/test_pthread_stub.out
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@@ -1,5 +1,6 @@
test_c11_threads
test_pthreads
__builtin_thread_pointer non-null: 1
cleanup: 42
test_pthread_getattr_np
stack_addr: 0, stack_size: 65536, guard_size: 8192
9 changes: 2 additions & 7 deletions tools/system_libs.py
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Expand Up @@ -1889,6 +1889,8 @@ class libmimalloc(MTLibrary):
'-DNDEBUG',
# Emscripten uses musl libc internally
'-DMI_LIBC_MUSL',
# enable use of `__builtin_thread_pointer()`
'-DMI_USE_BUILTIN_THREAD_POINTER',
]

# malloc/free/calloc are runtime functions and can be generated during LTO
Expand All @@ -1911,13 +1913,6 @@ class libmimalloc(MTLibrary):
# Include sbrk.c in libc, it uses tracing and libc itself doesn't have a tracing variant.
src_files += [utils.path_from_root('system/lib/libc/sbrk.c')]

def get_cflags(self):
cflags = super().get_cflags()
if self.is_mt:
# enable use of `__builtin_thread_pointer()` in multithreaded builds
cflags += ['-DMI_USE_BUILTIN_THREAD_POINTER']
return cflags

def can_use(self):
return super().can_use() and settings.MALLOC == 'mimalloc'

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