Re: [Tinycc-devel] lcall invalid hex code

[Michael Matz]

Hi,

On Sun, 1 May 2016, Sergey Korshunoff wrote:

> diff --git a/i386-asm.h b/i386-asm.h
> index 486cffe..637568b 100644
> --- a/i386-asm.h
> +++ b/i386-asm.h
> @@ -213,7 +213,7 @@ ALT(DEF_ASM_OP1(jmp, 0xff, 0, OPC_JMP | OPC_WL, OPT_REGW))
> #endif
> .
> ALT(DEF_ASM_OP2(lcall, 0x9a, 0, 0, OPT_IM16, OPT_IM32))
> -ALT(DEF_ASM_OP1(lcall, 0xff, 3, 0, OPT_EA))
> +ALT(DEF_ASM_OP1(lcall, 0xff1f, 3, 0, OPT_EA))
> ALT(DEF_ASM_OP2(ljmp, 0xea, 0, 0, OPT_IM16, OPT_IM32))
> ALT(DEF_ASM_OP1(ljmp, 0xff, 5, 0, OPT_EA))

You don't say what exactly you want to fix, but whatever it is, the patch 
is incorrect.  'lcall' is no two-byte opcode (those start with 0x0f), but 
rather the opcode is 0xff and the sub-opcode is in the mod/rm byte (aka. 
group #5 [1]).  It's sub-opcode 3, hence correct above.

If anything the decoding of the above table in i386-asm.c is wrong, but I 
can't say without knowing what the problem is.


Ciao,
Michael.
[1] See any decent x86 opcode listing, like sandpile.org or x86asm.net.