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gh-112535: Update _Py_ThreadId() to support PowerPC, IBM Z, etc #112553

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gh-112535: Update _Py_ThreadId() to support PowerPC, IBM Z, etc #112553

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2 changes: 2 additions & 0 deletions Include/object.h
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Original file line number Diff line number Diff line change
Expand Up @@ -261,6 +261,8 @@ _Py_ThreadId(void)
__asm__ ("mrs %0, tpidrro_el0" : "=r" (tid));
#elif defined(__aarch64__)
__asm__ ("mrs %0, tpidr_el0" : "=r" (tid));
#elif define(HAVE_BUILTIN_THREAD_POINTER)
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This line of the public C API which can be used by a C compiler different than the one used to build Python. I don't think that if define(HAVE_BUILTIN_THREAD_POINTER) check is reliable, according to what @colesbury wrote in the issue.

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I wrote "C compiler", but the C API can be parsed by parsers which are not C compiler, but written in any programming language. Moreover, the C API is used in C++.

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Ah got it, let me check :)

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@corona10 corona10 Nov 30, 2023 •
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. I don't think that if define(HAVE_BUILTIN_THREAD_POINTER) check is reliable
but the C API can be parsed by parsers which are not C compiler

Yeah, I thought that configuring time checking would be enough but it looks like we should consider 3rd party case.

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Yeah, I'm concerned that the compiler for CPython may be not exactly the same as the compiler for third-party extensions. For example, if we want to use __builtin_thread_pointer() for x86-64, it's available for GCC 11.1+, but an extension might be compiling with an older version of GCC that doesn't support it for that architecture.

Additionally, one thing to be careful of, is that macOS arm64 will successfully compile and run __builtin_thread_pointer(), but it returns the wrong value (CPU id).

PowerPC on GCC still requires a "register variable" https://github.com/bminor/glibc/blob/master/sysdeps/powerpc/nptl/thread_pointer.h (or it can fallback to a portable thread-local implementation, but that would be slower.)

tid = (uintptr_t)__builtin_thread_pointer();
#else
# error "define _Py_ThreadId for this platform"
#endif
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41 changes: 41 additions & 0 deletions configure
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17 changes: 17 additions & 0 deletions configure.ac
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Expand Up @@ -4541,6 +4541,23 @@ AS_VAR_IF([ac_cv_builtin_atomic], [yes], [
AC_DEFINE(HAVE_BUILTIN_ATOMIC, 1, [Has builtin __atomic_load_n() and __atomic_store_n() functions])
])

AC_CACHE_CHECK([for builtin __builtin_thread_pointer], [ac_cv_builtin_thread_pointer], [
AC_LINK_IFELSE(
[
AC_LANG_SOURCE([[
void *tp;
int main() {
tp = __builtin_thread_pointer();
return 0;
}
]])
],[ac_cv_builtin_thread_pointer=yes],[ac_cv_builtin_thread_pointer=no])
])

AS_VAR_IF([ac_cv_builtin_thread_pointer], [yes], [
AC_DEFINE(HAVE_BUILTIN_THREAD_POINTER, 1, [Has builtin __builtin_thread_pointer])
])

# --with-mimalloc
AC_MSG_CHECKING([for --with-mimalloc])
AC_ARG_WITH([mimalloc],
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3 changes: 3 additions & 0 deletions pyconfig.h.in
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Expand Up @@ -127,6 +127,9 @@
/* Has builtin __atomic_load_n() and __atomic_store_n() functions */
#undef HAVE_BUILTIN_ATOMIC

/* Has builtin __builtin_thread_pointer */
#undef HAVE_BUILTIN_THREAD_POINTER

/* Define to 1 if you have the <bzlib.h> header file. */
#undef HAVE_BZLIB_H

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