Re: [igt-dev] [PATCH i-g-t v2 1/4] meson: add libatomic dependency

[Guillaume Tucker <guillaume.tucker@collabora.com>]

On 14/06/2019 09:07, Ser, Simon wrote:
> On Thu, 2019-06-13 at 14:53 +0100, Guillaume Tucker wrote:
>> Add conditional dependency on libatomic in order to be able to use the
>> __atomic_* functions instead of the older __sync_* ones.  The
>> libatomic library is only needed when there aren't any native support
>> on the current architecture, so a linker test is used for this
>> purpose.  This enables atomic operations to be on a wider number of
>> architectures including MIPS.
>>
>> Signed-off-by: Guillaume Tucker <guillaume.tucker@collabora.com>
>> ---
>>  meson.build | 13 +++++++++++++
>>  1 file changed, 13 insertions(+)
>>
>> diff --git a/meson.build b/meson.build
>> index 6268c58d3634..da25a28f3268 100644
>> --- a/meson.build
>> +++ b/meson.build
>> @@ -179,6 +179,19 @@ math = cc.find_library('m')
>>  realtime = cc.find_library('rt')
>>  dlsym = cc.find_library('dl')
>>  zlib = cc.find_library('z')
>> +if cc.links('''
>> +#include <stdint.h>
>> +int main(void) {
>> +  uint32_t x32 = 0;
>> +  uint64_t x64 = 0;
>> +  __atomic_load_n(&x32, __ATOMIC_SEQ_CST);
>> +  __atomic_load_n(&x64, __ATOMIC_SEQ_CST);
> 
> Minor: maybe we could've used stdatomic.h's atomic_* functions (without
> the "__" prefix) for consistency with the actual IGT code?

I actually thought it was more correct to use the __atomic_*
functions directly from the libatomic library as this is a linker
test.  If for any reason stdatomic.h changes between versions or
compilers and uses something else than libatomic, then this test
would become invalid.

>> +  return 0;
>> +}''', name : 'built-in atomics')
>> +	libatomic = []
> 
> We could use null_dep instead, to make it consistent with the other
> branch.

Ack, will fix that in v3.

>> +else
>> +	libatomic = cc.find_library('atomic')
>> +endif
>>  
>>  if cc.has_header('linux/kd.h')
>>  	config.set('HAVE_LINUX_KD_H', 1)

Thanks,
Guillaume
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