Re: [Qemu-devel] FreeSBIE-20040919, ffreep insn

[Fabrice Bellard <fabrice@bellard.org>]

I don't think ffreep is used by the software you tried. It must be a bug 
which yields a jump in a data section. ffreep is not documented and it 
does not work on every CPU (I get an invalid instruction exception on 
P4), so I propose not to implement it.

Fabrice.

Juergen Lock wrote:
> Hi!  I just tried FreeSBIE-20040919,
> 	http://torrent.freesbie.org/FreeSBIE-20040919.iso.torrent
> and got an illegal instruction when starting X.  I gdb'd the core
> and found its the ffreep insn that it failed on:
> 	http://webster.cs.ucr.edu/AsmTools/NASM/Doc/NASMDOCA.HTM
> says its undocumented (A.55, does an ffree and then pops st0),
> so thats probably the reason why its missing.  So i added it:
> 
> Index: qemu/target-i386/translate.c
> @@ -3187,6 +3187,10 @@
>                      goto illegal_op;
>                  }
>                  break;
> +            case 0x38: /* ffreep sti */
> +                gen_op_ffree_STN(opreg);
> +                gen_op_fpop();
> +                break; 
>              case 0x3c: /* df/4 */
>                  switch(rm) {
>                  case 0:
> 
> and now X gets a bit further but then gets another illegal instruction,
> this time with a signal handler setup so i dont know the failed eip.
> (I guess i'd have to patch X to get it...)  But, later i started an xterm
> (displaying on the host), and that came up but then also died of an
> illegal instruction, this time it was xorps  %xmm0,%xmm0.  So i guess
> this FreeSBIE's X is built with -march=pentium3 or something.
> (What are the chances of adding sse to qemu?  I guess slim :)
> 
>  Anyway, I guess there's nothing wrong with adding ffreep...
> 	Juergen
> 
> 
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