On Mon, Jan 01, 2018 at 11:09:07PM +0200, Konstantin Belousov wrote:
On Mon, Jan 01, 2018 at 09:47:40PM +0100, Pierre DAVID wrote:

I'm on a recent current:
    FreeBSD biceps.ma.maison 12.0-CURRENT FreeBSD 12.0-CURRENT #2 r327239: Wed 
Dec 27 18:25:46 CET 2017     
p...@biceps.ma.maison:/usr/obj/usr/src/amd64.amd64/sys/BICEPS  amd64

with clang 5.0.1:
    FreeBSD clang version 5.0.1 (tags/RELEASE_501/final 320880) (based on LLVM 
    Target: x86_64-unknown-freebsd12.0
    Thread model: posix
    InstalledDir: /usr/bin

I'm having a problem with the following source file:

#include <stdatomic.h>

struct foo
    int f1 ;
    char f2 ;
    int f3 ;
} ;

_Atomic struct foo a ;
struct foo b ;

int main (int argc, char *argv [])
    b = (struct foo) {.f1 = 5, .f2 = 7, .f3 = 9 } ;
    // atomic_store (&a, b) ;
    a = b ;

This code does not compile/link with:
    % cc foo.c -lstdthreads
    /tmp/foo-a0ef26.o: In function `main':
    foo.c:(.text+0x63): undefined reference to `__sync_lock_test_and_set_16'
    cc: error: linker command failed with exit code 1 (use -v to see invocation)

The gcc internal seems to be linked as "cc -v" told me:
    % cc -v foo.c -lstdthreads
     "/usr/bin/ld" --eh-frame-hdr -dynamic-linker /libexec/ld-elf.so.1 
--hash-style=both --enable-new-dtags -o a.out /usr/lib/crt1.o /usr/lib/crti.o 
/usr/lib/crtbegin.o -L/usr/lib /tmp/foo-d7a21b.o -lstdthreads -lgcc --as-needed -lgcc_s 
--no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/crtend.o 

The problem occurs with "atomic_store(&a, b)" as well as with "a = b".

If I remove the f3 member, the struct foo is only 8 bytes and the code

Did I missed something?

clang issues a calls to libatomic, which we do not provide.
As a workaround, use the following command to compile.  The resulting
binary works on all practically usable machines.
        $ cc -march=core2 source.c
You might want to turn off sse3/4.1 if you are concerned about older pentium4.

Thanks for your help. I wish that the C11 status of FreeBSD will soon
be complete out of the box, without the help of such a hack.

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