Re: Glitches in gas/objdump handling of i386 STR, SLDT, SMSW instructions

["H . J . Lu" <hjl at lucon dot org>]

On Sun, Nov 11, 2001 at 04:19:11PM -0800, Zack Weinberg wrote:
> A comment on linux-kernel led me to discover some bugs in gas and
> objdump -d handling of the STR and SMSW instructions.
> 
> First and most seriously: gas incorrectly thinks STR is invalid except
> with a 16-bit operand.  In reality, STR works like most i386
> word/long/quad instructions: the operand size prefixes apply.  To
> demonstrate this, compile and run this test program:
...
> The same bug applies to the SLDT and SMSW instructions, although GAS
> gets them right.
> 
> I believe this is an appropriate patch.  I've run test files
> containing STR, SMSW, and SLDT instructions through the resultant as
> and objdump, but I haven't done a full build+test cycle.  Nor have I
> checked the rest of the segment instructions thoroughly.
> 
> zw
> 
> 	* include/opcode/i386.h: Change "str" instruction to
> 	wlq_Suf|Modrm, WordReg|WordMem.
> 	* opcodes/i386-dis.c: Change "sldt", "str", and "smsw" entries
> 	to "sldtQ", "strQ", "smswQ" respectively; all with Ev operand
> 	category instead of Ew.
> 
> ===================================================================
> Index: include/opcode/i386.h
> --- include/opcode/i386.h	2001/05/12 09:52:39	1.33
> +++ include/opcode/i386.h	2001/11/12 00:11:42
> @@ -555,7 +555,7 @@ static const template i386_optab[] = {
>  {"sidt",   1, 0x0f01, 1, Cpu286, wlq_Suf|Modrm,		{ WordMem, 0, 0} },
>  {"sldt",   1, 0x0f00, 0, Cpu286, wlq_Suf|Modrm,		{ WordReg|WordMem, 0, 0} },
>  {"smsw",   1, 0x0f01, 4, Cpu286, wlq_Suf|Modrm,		{ WordReg|WordMem, 0, 0} },
> -{"str",	   1, 0x0f00, 1, Cpu286, w_Suf|Modrm|IgnoreSize,{ Reg16|ShortMem, 0, 0} },
> +{"str",	   1, 0x0f00, 1, Cpu286, wlq_Suf|Modrm,		{ WordReg|WordMem, 0, 0} },
>  

I don't think it is right. "str" takes a 16bit reg/mem or 32bit reg,
according to Intel ia32 manual.


H.J.