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meson: always use libatomic if found

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Semi-quoting https://github.com/systemd/systemd/issues/25057:

clang-16 has made the choice to turn on -Werror=implicit-function-declaration,implicit-int.
(See Gentoo's tracker bug https://bugs.gentoo.org/870412).
Added in commit 132c73b57a, systemd now does a
check to see if libatomic is needed with some compile/link tests with e.g.
__atomic_exchange_1, but the tests don't provide a prototype for
__atomic_exchange_1 so with clang-16 the test fails, breaking the build.

Let's simplify things by linking to libatomic unconditionally if it is found
and seems to work. If actually unneeded, it might be dropped via --as-needed.
This seems to work with gcc and clang.

declare_dependency() is used instead of cc.find_library(), because the latter
picks up a symlink in gcc private directory (e.g.
/usr/lib/gcc/x86_64-redhat-linux/12/libatomic.so), and we don't want that.

Fixes #25057.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2022-10-19 16:23:41 +02:00 committed by Luca Boccassi
parent 2051a98172
commit 96f8c63601
1 changed files with 11 additions and 10 deletions
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21
meson.build
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@ -1013,22 +1013,23 @@ endif
#####################################################################
libatomic = []
if not cc.links('''#include <stdint.h>
int main() {
char i;
__atomic_exchange_1(&i, 1, 0);
return 1;
}''',
name : 'Atomic builtin requires -latomic')
libatomic = cc.find_library('atomic')
endif
threads = dependency('threads')
librt = cc.find_library('rt')
libm = cc.find_library('m')
libdl = cc.find_library('dl')
libcrypt = cc.find_library('crypt')
# On some architectures, libatomic is required. But on some installations,
# it is found, but actual linking fails. So let's try to use it opportunistically.
# If it is installed, but not needed, it will be dropped because of --as-needed.
if cc.links('''int main(int argc, char **argv) { return 0; }''',
args : '-latomic',
name : 'libatomic')
libatomic = declare_dependency(link_args : '-latomic')
else
libatomic = []
endif
crypt_header = conf.get('HAVE_CRYPT_H') == 1 ? '''#include <crypt.h>''' : '''#include <unistd.h>'''
foreach ident : [
['crypt_ra', crypt_header],