[FFmpeg-devel] [PATCH 1/2] libavutil: Add av_visibility_hidden for setting hidden symbol visibility

[Triang3l]

Yes, making everything except for av_ hidden by default would be more 
consistent with the current build process, which includes libavcodec.v. 
Though, this is a special case that results not only in increasing the 
shared object file size if libavcodec.v is not used, which is 
undesirable, yet harmless, but also in making the library not linkable 
with PIC at all unless those symbols are hidden or forced to be resolved 
at link time some other way.

Thanks for implementing the fix very quickly, by the way!

I'd also suggest writing a comment in the code describing specifically 
the original issue that the current instances of the usage of 
visibility("hidden") resolves, so the reason why it's used there is not 
forgotten, and there's a clear pattern of relation between movrel X() 
and av_visibility_hidden to follow when adding new assembly code. Though 
if the convention is to rely on `git blame` for this purpose, that 
shouldn't be necessary.

— Triang3l

On 11/07/2022 15:12, Henrik Gramner wrote:
> On Mon, Jul 11, 2022 at 11:19 AM Martin Storsjö <martin at martin.st> wrote:
>> +#if (AV_GCC_VERSION_AT_LEAST(4,0) || defined(__clang__)) && (defined(__ELF__) || defined(__MACH__))
>> +#    define av_visibility_hidden __attribute__((visibility("hidden")))
>> +#else
>> +#    define av_visibility_hidden
>> +#endif
> The usual approach is to compile with -fvisibility=hidden and
> explicitly flag exported API symbols.
>
> Is there a reason for doing this the other way around?
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