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

Michael Niedermayer michaelni
Thu Mar 8 22:42:34 CET 2007


Hi

On Thu, Mar 08, 2007 at 09:46:33PM +0100, Panagiotis Issaris wrote:
> Hi
> 
> Michael Niedermayer schreef:
> > On Thu, Mar 08, 2007 at 07:46:55PM +0100, Panagiotis Issaris wrote:
> >> Michael Niedermayer schreef:
> >>> On Thu, Mar 08, 2007 at 06:16:46PM +0100, Guillaume Poirier wrote:
> >>>> Panagiotis Issaris wrote:
> >>>>> When configuring FFmpeg revision 8295 (most recent SVN) to disable
> >>>>> optimizations (for easier debugging), the cabac.c file fails to compile:
> >>>>> "can't find a register in class ???GENERAL_REGS??? while reloading ???asm???"
> >>>>>
> >>>>> I've tried using several versions of GCC. Any tips on how to fix this?
> >>>>[...]
> >>> what would be correct is:
> >>> #if defined(ARCH_X86) && defined(CONFIG_EBP) && defined(CONFIG_EBX)
> >> What would CONFIG_EBP mean? Looking at the naming of the other CONFIG_*
> >> options, I'd say it means the "EBP" and "EBX" "features" would be
> >> enabled :) although it is quite unlikely EBP and EBX have other meanings
> >> than the obvious (register names).
> > 
> > yes CONFIG_EBP means that the EBP register is available
> > with gcc this is the case if and only if -fomit-frame-pointer is used
> This indeed fails to compile if -fomit-frame-pointer isn't used _if_
> optimization is turned on:
> 
> int main() { asm volatile ("" ::: "ebp"); }
> 
> With -O0 or without -Ox flag (which is what is used when --enable-opts
> is passed to configure) the testapp compiles fine in either case.
> 
> So, with the flags used for the compilation of cabac.c, the testapp
> compiles fine.

compiles yes, works no

try
int main() {
    volatile int i=0;
    asm volatile (
        "xorl %%ebp, %%ebp"
    ::: "%ebp");
    return i;
}

this will crash with -O0 and without -fomit-frame-pointer

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

If you really think that XML is the answer, then you definitly missunderstood
the question -- Attila Kinali
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