[Ffmpeg-devel] Re: Broken trunk on AMD64 with PIC enabled

Michael Niedermayer michaelni
Thu Apr 5 00:35:04 CEST 2007


On Wed, Apr 04, 2007 at 12:56:46PM -0700, Trent Piepho wrote:
> On Wed, 4 Apr 2007, Michael Niedermayer wrote:
> > ive already said i ve no time ATM (yeah google soc ...) for this disscussion
> > which is likely why you and uoti continue it instead of providing any useable
> > help in correcting the problem (that is a patch we can apply ...)
> I don't have an amd64 system, so there is no way I can provide a tested
> patch.  I think Diego Petten??'s patch that he already sent to the list is
> probably the best that one can hope for.  The asm code used in cabac.h
> isn't suitable for a x86-64 DSO.  In order to use an asm cabac in a x86-64
> DSO, new asm must be used, and something as simple as changing MANGLE isn't
> enough to do it.  IMHO, tt hardly seems worth the trouble.

hmm, well, ive no objections to his patch which disabled the affected code on
x86-64 && PIC its better than the current situation 

> > also rip relative is also limited to 32bit offsets ...
> But that 4GB space can be anywhere in the 64-bit address space.

hmm, first IIRC x86-64 doesnt truely support 64bit addressing but rather 
48bit or so, but i might be wrong, ive not checked the docs i am just
repeating what i read here sometime ago ...

second part is that the loader/OS has no reason to use more address space
than needed for placing the shared libs, its even likey a very bad idea
cache wise
so rip relative addressing breaks as soon as a single shared lib is 2gb
this is not likely currently, and relocations break if all used shared
libs for one process exceed 4gb this too is unlikely and when it does
fail the rip relative failure would likely happen soon thereafter too ...

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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