[Ffmpeg-devel] [patch] gcc4 visibility support

Luca Barbato lu_zero
Fri Jun 2 18:39:20 CEST 2006

Mike Melanson wrote:
> Could you explain this a bit? What is meant by "gcc visibility"? A
> cursory review of the patch seems to indicate that public symbols in the
> C files are now qualified with the keyword EXPORTED. What's this all
> about? I haven't heard of this before.

gcc-4 added support for -fvisibility*, a way to define if you want
export or not certain symbols marking them with an specific
__attribute__ and defining the default elsewhere. Usually you set the
default to hidden and just mark as visible the symbols you care about.
That's is quite a boon on C++ bloated projects, but is also nice for C libs.

here follows the used car speech about it (from manpages)

           Set the default ELF image symbol visibility to the specified
           option---all symbols will be marked with this unless 	
	   overridden within the code.  Using this feature can very
	   substantially improve linking and load times of shared object
	   libraries, produce more optimized code, provide near-perfect
	   API export and prevent symbol clashes.  It is strongly
	   recommended that you use this in any shared objects you

By marking explicitly what's is public api and what's not and enforcing
it you make less likely having programs broken because of internal
changes in ffmpeg beside the other promoted goods.



Luca Barbato

Gentoo/linux Gentoo/PPC

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