[vlc-devel] [PATCH] aout/coreaudio: Use symbols directly instead of dlsym

[Rémi Denis-Courmont]

Hi,

Similar to weak ELF symbols then but they're a bit questionable for C/C++ semantics. A function cannot compare nul, as opposed to a function pointer.

Le 2 août 2019 16:24:53 GMT+03:00, Marvin Scholz <epirat07 at gmail.com> a écrit :
>On 2 Aug 2019, at 14:45, Rémi Denis-Courmont wrote:
>
>> Hi,
>>
>> That's not how symbol resolution normally works... Are you sure?
>
>Yes, thats the concept of partially available symbols (requires special
>annotation in the function declaration) which allows symbols to be 
>undefined
>without causing a failure at runtime (essentially a weak symbol).
>
>Most macOS headers use some complex macro magic to mark symbols as 
>partially
>available (weak) when targeting macOS versions that are lower than the 
>macOS
>version where the symbol was introduced.
>
>The user must then check if the symbol is NULL before using it or just 
>check
>the macOS version.
>
>The header declaring the symbol has it annotated correctly:
>https://opensource.apple.com/source/libplatform/libplatform-125/include/os/lock.h.auto.html
>
>>
>> Le 2 août 2019 14:59:13 GMT+03:00, Marvin Scholz <epirat07 at gmail.com>
>
>> a écrit :
>>> It is not needed to load the symbols using dlsym here, they will be
>>> automatically available if the OS version is recent enough or NULL
>if
>>> not.
>>> ---
>>> modules/audio_output/coreaudio_common.c | 4 ++--
>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/modules/audio_output/coreaudio_common.c
>>> b/modules/audio_output/coreaudio_common.c
>>> index 3a9ec69113..836a5f6de4 100644
>>> --- a/modules/audio_output/coreaudio_common.c
>>> +++ b/modules/audio_output/coreaudio_common.c
>>> @@ -63,10 +63,10 @@ ca_ClearOutBuffers(audio_output_t *p_aout)
>>> static void
>>> ca_init_once(void)
>>> {
>>> -    unfair_lock.lock = dlsym(RTLD_DEFAULT, "os_unfair_lock_lock");
>>> +    unfair_lock.lock = os_unfair_lock_lock;
>>>     if (!unfair_lock.lock)
>>>         return;
>>> -    unfair_lock.unlock = dlsym(RTLD_DEFAULT, 
>>> "os_unfair_lock_unlock");
>>> +    unfair_lock.unlock = os_unfair_lock_unlock;
>>>     if (!unfair_lock.unlock)
>>>         unfair_lock.lock = NULL;
>>>
>>> -- 
>>> 2.19.1
>>>
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>>
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