[Mesa-dev] Fix __atomic* builtins detection for Clang

[Jan Beich]

Jonathan Gray <jsg at jsg.id.au> writes:

> On Sat, May 13, 2017 at 02:22:30AM +0200, Jan Beich wrote:
>
>> "int" isn't large enough and lack of builtins only manifests at link time.
>> This was breaking build on FreeBSD 11.0 i386 with Clang 3.8.0.
>> 
>> glsl/.libs/libstandalone.a(libmesautil_la-disk_cache.o): In function `disk_cache_remove':
>> disk_cache.c:(.text+0x763): undefined reference to `__atomic_fetch_add_8'
>> glsl/.libs/libstandalone.a(libmesautil_la-disk_cache.o): In function `cache_put':
>> disk_cache.c:(.text+0xabc): undefined reference to `__atomic_fetch_add_8'
>> disk_cache.c:(.text+0xec1): undefined reference to `__atomic_fetch_add_8'
>> c++: error: linker command failed with exit code 1 (use -v to see invocation)
>
> You should be building with -march=i586 on i386 for CX8.

-march=i586 doesn't help. Dimitry, could this be a Clang bug?

$ cat a.c
#include <stdint.h>
int main() {
    uint64_t n;
    return __atomic_load_n(&n, __ATOMIC_ACQUIRE);
}

$ clang40 -m32 -march=i586 a.c
/tmp/a-d984ec.o: In function `main':
a.c:(.text+0x21): undefined reference to `__atomic_load_8'
clang-4.0: error: linker command failed with exit code 1 (use -v to see invocation)

full build log: http://sprunge.us/LJdh

>
> The diff is wrong as it will break other architectures, ie powerpc.

And it's not broken already? -latomic isn't passed anywhere.

>
> commit a6a38a038bd62e6d9558905f00bef81b5e7e6fcc
> Author: Grazvydas Ignotas <notasas at gmail.com>
> Date:   Fri Mar 31 01:26:25 2017 +0300
>
>     util/u_atomic: provide 64bit atomics where they're missing
>
> attempts to handle powerpc like situations, though not sync
> builtins being missing entirely.
>
>> ---
>>  configure.ac | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>> 
>> diff --git a/configure.ac b/configure.ac
>> index 957d15df8c..5b11941a0c 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -403,9 +403,10 @@ AM_CONDITIONAL([SSE41_SUPPORTED], [test x$SSE41_SUPPORTED = x1])
>>  AC_SUBST([SSE41_CFLAGS], $SSE41_CFLAGS)
>>  
>>  dnl Check for new-style atomic builtins
>> -AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
>> +AC_LINK_IFELSE([AC_LANG_SOURCE([[
>> +#include <stdint.h>
>>  int main() {
>> -    int n;
>> +    uint64_t n;
>>      return __atomic_load_n(&n, __ATOMIC_ACQUIRE);
>>  }]])], GCC_ATOMIC_BUILTINS_SUPPORTED=1)
>>  if test "x$GCC_ATOMIC_BUILTINS_SUPPORTED" = x1; then
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev