[FFmpeg-devel] [PATCH] split-radix FFT

[Michael Niedermayer]

On Tue, Jul 29, 2008 at 09:21:32PM +0300, Uoti Urpala wrote:
> On Tue, 2008-07-29 at 19:38 +0200, Michael Niedermayer wrote:
> > On Tue, Jul 29, 2008 at 06:57:21PM +0300, Uoti Urpala wrote:
> > > On Tue, 2008-07-29 at 17:41 +0200, Michael Niedermayer wrote:
> > > > x86-64 shared libs require -fPIC, unless that has been fixed.
> > > > so the user does not always have the option to omit -fPIC
> > > 
> > > I didn't mean to include AMD64 in x86. -fPIC does not cause that much
> > > slowdown on it. And anyway what shared libs on AMD64 require is *no
> > > textrels* - generating them by some other method wouldn't work any
> > > better. So you don't need MANGLE to force creating textrels, and if it
> > > did that the result in fact wouldn't work. You can avoid GOT lookup by
> > > adding visibility information (and then the compiler will avoid it for
> > > ALL uses, not just those inside asm).
> > 
> > We dont have visibility attributes in svn,
> 
> I'm not aware of any significant difficulties with adding them, less
> still for the subset of symbols that are candidates for MANGLE.
> 
> > they are a gcc only feature and
> 
> No more so than inline asm which can use MANGLE. The __attribute__
> syntax for declaring them is specific to GCC/ICC but if you use macros
> there are more compilers that support some visibility syntax than
> compilers that support MANGLE.
> 
> > I think noone came up with a clean way to add visibility attributes,
> > that is a way that does not require adding them to a significant
> > portion of the globals one by one.
> 
> I've explained that before. I don't think adding them per global is a
> particular problem (though somewhat more work); they're conceptually
> similar to "static" which is also used per symbol. You can also set the
> default visibility for a portion of the file so it will be used for all
> symbols defined/declared there.

Iam not strongly opposed to a patch that adds them one by one to the
exported globals or cleanly splits header files into internal & external
where this is not done yet and sets visibility per file.
But i wont do it myself, id just review the patch!
Also such a patch would not allow us to remove all the MANGLE() they still
would be needed for forcing textrels on x86-32 and for old gcc versions.


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When the tyrant has disposed of foreign enemies by conquest or treaty, and
there is nothing more to fear from them, then he is always stirring up
some war or other, in order that the people may require a leader. -- Plato
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