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Merged
vstinner merged 3 commits into from
Sep 8, 2023
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gh-109054: configure checks if libatomic is needed #109101

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efd3ec2
gh-109054: configure checks if libatomic is needed
vstinner Sep 7, 2023
22f3b86
Fix: don't declare LIBATOMIC
vstinner Sep 8, 2023
086303f
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vstinner Sep 8, 2023
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6 changes: 6 additions & 0 deletions Misc/NEWS.d/next/Build/2023-09-07-19-58-05.gh-issue-109054.5r3S3l.rst
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@@ -0,0 +1,6 @@
Fix building the ``_testcapi`` extension on Linux AArch64 which requires
linking to libatomic when ``<cpython/pyatomic.h>`` is used: the
``_Py_atomic_or_uint64()`` function requires libatomic
``__atomic_fetch_or_8()`` on this platform. The configure script now checks
if linking to libatomic is needed and generates a new LIBATOMIC variable
used to build the _testcapi extension. Patch by Victor Stinner.
85 changes: 84 additions & 1 deletion configure
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62 changes: 61 additions & 1 deletion configure.ac
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Expand Up@@ -6962,6 +6962,62 @@ then
[Define if you want to disable the GIL])
fi

# gh-109054: Check if -latomic is needed to get <pyatomic.h> atomic functions.
# On Linux aarch64, GCC may require programs and libraries to be linked
# explicitly to libatomic. Call _Py_atomic_or_uint64() which may require
# libatomic __atomic_fetch_or_8(), or not, depending on the C compiler and the
# compiler flags.
#
# Avoid #include <Python.h> or #include <pyport.h>. The <Python.h> header
# requires <pyconfig.h> header which is only written below by AC_OUTPUT below.
# If the check is done after AC_OUTPUT, modifying LIBATOMIC has no effect
# anymore. <pyport.h> cannot be included alone, it's designed to be included
# by <Python.h>: it expects other includes and macros to be defined.
_SAVE_VAR([CPPFLAGS])
CPPFLAGS="${BASECPPFLAGS} -I. -I${srcdir}/Include ${CPPFLAGS}"

AC_CACHE_CHECK([whether libatomic is needed by <pyatomic.h>],
[ac_cv_libatomic_needed],
[AC_RUN_IFELSE([AC_LANG_SOURCE([[
// pyatomic.h needs uint64_t and Py_ssize_t types
#include <stdint.h> // int64_t, intptr_t
#ifdef HAVE_SYS_TYPES_H
# include <sys/types.h> // ssize_t
#endif
// Code adapted from Include/pyport.h
#if HAVE_SSIZE_T
typedef ssize_t Py_ssize_t;
#elif SIZEOF_VOID_P == SIZEOF_SIZE_T
typedef intptr_t Py_ssize_t;
#else
# error "unable to define Py_ssize_t"
#endif

#include "cpython/pyatomic.h"

int main()
{
uint64_t byte;
_Py_atomic_store_uint64(&byte, 2);
if (_Py_atomic_or_uint64(&byte, 8) != 2) {
return 1; // error
}
if (_Py_atomic_load_uint64(&byte) != 10) {
return 1; // error
}
return 0; // all good
}
]])],[
ac_cv_libatomic_needed=no
],[ac_cv_libatomic_needed=yes],[ac_cv_libatomic_needed=yes])
])

AS_VAR_IF([ac_cv_libatomic_needed], [yes],
[LIBATOMIC=${LIBATOMIC-"-latomic"}])

@erlend-aaslanderlend-aaslandSep 8, 2023

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I just realised we could probably just use ${VAR="default"} instead of the more verbose VAR=${VAR-"default"}. However, let's stick to the existing practise :) And hopefully, configure.ac is git rm'd some day.

_RESTORE_VAR([CPPFLAGS])


# stdlib
AC_DEFUN([PY_STDLIB_MOD_SET_NA], [
m4_foreach([mod], [$@], [
AS_VAR_SET([py_cv_module_]mod, [n/a])])
Expand DownExpand Up@@ -7229,7 +7285,10 @@ PY_STDLIB_MOD([_hashlib], [], [test "$ac_cv_working_openssl_hashlib" = yes],
[$OPENSSL_INCLUDES], [$OPENSSL_LDFLAGS $OPENSSL_LDFLAGS_RPATH $LIBCRYPTO_LIBS])

dnl test modules
PY_STDLIB_MOD([_testcapi], [test "$TEST_MODULES" = yes])
PY_STDLIB_MOD([_testcapi],
[test "$TEST_MODULES" = yes], []
dnl Modules/_testcapi/pyatomic.c uses <cpython/pyatomic.h> header
[], [], [$LIBATOMIC])
PY_STDLIB_MOD([_testclinic], [test "$TEST_MODULES" = yes])
PY_STDLIB_MOD([_testclinic_limited], [test "$TEST_MODULES" = yes])
PY_STDLIB_MOD([_testinternalcapi], [test "$TEST_MODULES" = yes])
Expand DownExpand Up@@ -7262,6 +7321,7 @@ AC_CONFIG_FILES(m4_normalize([
Modules/Setup.stdlib
]))
AC_CONFIG_FILES([Modules/ld_so_aix], [chmod +x Modules/ld_so_aix])
# Generate files like pyconfig.h
AC_OUTPUT

AC_MSG_NOTICE([creating Modules/Setup.local])
Expand Down