[Ffmpeg-devel] [BUG] Compilation failure when using --disable-opts

Zuxy Meng zuxy.meng
Thu Mar 15 02:30:17 CET 2007


2007/3/15, Michael Niedermayer <michaelni at gmx.at>:
> Hi
> On Thu, Mar 15, 2007 at 12:44:03AM +0000, M?ns Rullg?rd wrote:
> >
> > What I meant was, is ebx ever reserved the same way on x86_64?
> i dont know what gcc does with PIC on x86-64 maybe it doesnt reserve ebx/rbx
> after all theres no technical reason why it reserves it on x86-32 it could
> just handle the extra indirection over the GOT table like any other pointer
> dereference in C

x86-64 uses $rip relative addressing instead of #rbx for PIC code. I
guess the %ebx usage as a GOT base register is in the ABI.

> > With 8
> > more registers, it seem to me there should be enough for both a frame
> > pointer and whatever registers the inline asm needs.  Even if ebx is
> > reserved, some other register could be used by the assembler code.
> yes, of course but the existing asm code which has been written with
> x86-32 in mind uses ebx, why doesnt it ask gcc for any register with "r"
> well either because that was slower (see cabac code and ask gcc devels
> why) or because it lead to misscompiled code on some gcc versions or
> because the author was lazy

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While truth is beauty.
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