[Ffmpeg-devel] Segfault when encoding MPEG with MMX support

[Michael Niedermayer]

Hi

On Monday 11 July 2005 20:15, Tobias Grimm wrote:
> Michael Niedermayer schrieb:
> >writing it or similar), the code makes no sense and cannot work
>
> Ok - I will start with a fresh copy and try to make it PIC-compilable.
>
> Let's take this codeblock:
>
> ----
>
> asm volatile(
>     "movd %%"REG_a", %%mm3        \n\t" // last_non_zero_p1
>     SPREADW(%%mm3)
>     "pxor %%mm7, %%mm7            \n\t" // 0
>     "pxor %%mm4, %%mm4            \n\t" // 0
>     "movq (%2), %%mm5            \n\t" // qmat[0]
>     "pxor %%mm6, %%mm6            \n\t"
>     "psubw (%3), %%mm6            \n\t" // -bias[0]
>     "mov $-128, %%"REG_a"        \n\t"
>     ".balign 16                \n\t"
>     "1:                    \n\t"
>     "pxor %%mm1, %%mm1            \n\t" // 0
>     "movq (%1, %%"REG_a"), %%mm0    \n\t" // block[i]
>     "pcmpgtw %%mm0, %%mm1        \n\t" // block[i] <= 0 ? 0xFF : 0x00
>     "pxor %%mm1, %%mm0            \n\t"
>     "psubw %%mm1, %%mm0            \n\t" // ABS(block[i])
>     "psubusw %%mm6, %%mm0        \n\t" // ABS(block[i]) + bias[0]
>     "pmulhw %%mm5, %%mm0        \n\t" // (ABS(block[i])*qmat[0] -
> bias[0]*qmat[0])>>16
>     "por %%mm0, %%mm4            \n\t"
>     "pxor %%mm1, %%mm0            \n\t"
>     "psubw %%mm1, %%mm0            \n\t" // out=((ABS(block[i])*qmat[0]
> - bias[0]*qmat[0])>>16)*sign(block[i])
>     "movq %%mm0, (%5, %%"REG_a")    \n\t"
>     "pcmpeqw %%mm7, %%mm0        \n\t" // out==0 ? 0xFF : 0x00
>     "movq (%4, %%"REG_a"), %%mm1    \n\t"
>     "movq %%mm7, (%1, %%"REG_a")    \n\t" // 0
>     "pandn %%mm1, %%mm0            \n\t"
>     PMAXW(%%mm0, %%mm3)
>     "add $8, %%"REG_a"            \n\t"
>     " js 1b                \n\t"
>     "movq %%mm3, %%mm0            \n\t"
>     "psrlq $32, %%mm3            \n\t"
>     PMAXW(%%mm0, %%mm3)
>     "movq %%mm3, %%mm0            \n\t"
>     "psrlq $16, %%mm3            \n\t"
>     PMAXW(%%mm0, %%mm3)
>     "movd %%mm3, %%"REG_a"        \n\t"
>     "movzb %%al, %%"REG_a"        \n\t" // last_non_zero_p1
>
>     : "+a" (last_non_zero_p1)
>     : "r" (block+64), "r" (qmat), "r" (bias),
>
>       "r" (inv_zigzag_direct16+64), "r" (temp_block+64)
> );
>
> ----
>
> The compiler complains this, when using -fPIC:
>
> i386/mpegvideo_mmx_template.c: In Funktion ?dct_quantize_MMX?:
> i386/mpegvideo_mmx_template.c:93: error: can't find a register in class
> `GENERAL _REGS' while reloading `asm'
>
>
> The problem seems to be with the operands - gcc seems to run out of
> registers (one more register is available in non-PIC-mode). What can be
> done? Split the asm block? How?

add -fomit-frame-pointer to the flags or split it before "mov $-128, %%"REG_a"

[...]
-- 
Michael