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Document FF_SYMVER and attribute_used

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Originally committed as revision 23622 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer 2010-06-16 04:53:09 +00:00
parent d9aac26761
commit 33586ee770
1 changed files with 15 additions and 0 deletions
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15
libavutil/internal.h
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@ -46,6 +46,12 @@
#endif
#endif
/**
* Marks a variable as used and prevents the compiler from optimizing it away.
* This is usefull for asm that accesses varibles in ways that the compiler doesnt
* understand
*/
#ifndef attribute_used
#if AV_GCC_VERSION_AT_LEAST(3,1)
# define attribute_used __attribute__((used))
@ -196,6 +202,15 @@
# define NULL_IF_CONFIG_SMALL(x) x
#endif
/**
* Create a non default alias for a function with specified version.
* This is needed when symbols are moved from a lib to a dependancy of the lib
* because the gnu linker as of 2010 is buggy and fails to dynamicaly link if a symbol
* is not found in the lib in which it was during link time with enabled versioning
* even if a correctly versioned and matching symbol exists in another lib and
* even if it did find that would it not contain an explicit check to fail
*/
#if HAVE_SYMVER_ASM_LABEL
# define FF_SYMVER(type, name, args, ver) \
type ff_##name args __asm__ (EXTERN_PREFIX #name "@" ver); \