* Re: i386 - GAS problem (fwd)
[not found] <ECS9803211657D@utoronto.ca>
@ 1998-03-21 22:55 ` H.J. Lu
0 siblings, 0 replies; 3+ messages in thread
From: H.J. Lu @ 1998-03-21 22:55 UTC (permalink / raw)
To: Erik Ivanenko; +Cc: gas2, Ian Lance Taylor
>
>
>
>
> On Fri, 20 Mar 1998 18:02:00 -0500 H.J. Lu wrote:
>
> > From: H.J. Lu <hjl@lucon.org>
> > Date: Fri, 20 Mar 1998 18:02:00 -0500
> > Subject: Re: i386 - GAS problem (fwd)
> > To: Joel Sherrill <joel@OARcorp.com>
> > Cc: erik.ivanenko@utoronto.ca, gas2@cygnus.com
> >
> > > Date: Fri, 20 Mar 1998 15:38:16 -0500
> > > From: "erik.ivanenko" <erik.ivanenko@utoronto.ca>
> > > To: Joel Sherrill <joel@OARcorp.com>
> > > Subject: Re: i386 - GAS problem
> > >
> > > Joel Sherrill wrote:
> > >
> > > > Could you put together a small compilable file
> with this in it? binutils
> > > > 2.9 is getting closer and we don't want problems
> like this in there.
> > >
> > > The following file shows that the ds register is
> ignored by the lidt and
> > > lgdt instructions.This is also a problem with the
> GAS I have ( shipped with
> > > gcc-2.7.2.1 , Linux Universe version ).
> > > I suspect this has been there for a while.
> > >
> > > .section .text
> > > .code16
> > > movw $0x1000, %ax
> > > movw %ax, %ds
> > >
> > > lidt %ds:0x1000
> > > lidt 0x1000
> > >
> > > lgdt %ds:0x1000
> > > lgdt 0x1000
> > >
> > > .code32
> > >
> > > lidt %ds:0x1000
> > > lidt 0x1000
> > >
> > > lgdt %ds:0x1000
> > > lgdt 0x1000
> > >
> >
> > They look ok to me. Please tell me if you run into any
> real problems
> > with your programs.
> >
> > Correct me if I am wrong. I believe %ds is the default
> segment
> > register for lidt/lgdt. gas just optimizes it out.
> >
> >
> > H.J.
>
> I don't think that ds is used as a default for these
> instructions:
>
> The code that used these instructions loaded ds with
> 0x100, and used a 0x0 offset. The lidt failed; a logica
> analyzer showed memory writes starting at address 0.
>
> It was re-written into an equivalent form: ds contained
> 0x0 with offset 0x1000. That code worked; the logic
> analyzer showed memory writes starting at address
> 0x1000.
>
> The 386sx programmers manual states that the lidt and
> lgdt instructions take either m16:24 or m16:32
> arguments. The manual claims that the address follows
> the opcode directly.
>
> I don't have it in front of me,but I will try to remind
> myself to send you the exact wording on Monday.
>
Ian, I think lidt/lgdt are only 2 special cases which use
the linear address only. Here is a patch which seems to
work for me.
Thanks.
--
H.J. Lu (hjl@gnu.org)
---
Sat Mar 21 22:47:13 1998 H.J. Lu (hjl@gnu.org)
* config/tc-i386.c (md_assemble): Don't update "default_seg"
if the instruction uses linear address only.
* config/tc-i386.h (LinearAddress): New to indicate the
instruction using linear address only.
Index: gas/config/tc-i386.c
===================================================================
RCS file: /home/work/cvs/gnu/binutils/gas/config/tc-i386.c,v
retrieving revision 1.30
diff -u -p -r1.30 tc-i386.c
--- gas/config/tc-i386.c 1998/03/21 02:02:54 1.30
+++ gas/config/tc-i386.c 1998/03/22 06:33:14
@@ -1563,7 +1563,7 @@ md_assemble (line)
/* Find the default segment for the memory operand.
Used to optimize out explicit segment specifications. */
- if (i.seg)
+ if (i.seg && !(t->opcode_modifier & LinearAddress))
{
unsigned int seg_index;
Index: gas/config/tc-i386.h
===================================================================
RCS file: /home/work/cvs/gnu/binutils/gas/config/tc-i386.h,v
retrieving revision 1.17
diff -u -p -r1.17 tc-i386.h
--- gas/config/tc-i386.h 1997/11/01 03:09:10 1.17
+++ gas/config/tc-i386.h 1998/03/22 06:24:59
@@ -297,6 +297,8 @@ typedef struct
#define Data16 0x20000 /* needs data prefix if in 32-bit mode */
#define Data32 0x40000 /* needs data prefix if in 16-bit mode */
#define iclrKludge 0x80000 /* used to convert clr to xor */
+/* Indicate the instruction using linear address only */
+#define LinearAddress 0x100000
/* (opcode_modifier & COMES_IN_ALL_SIZES) is true if the
instuction comes in byte, word, and dword sizes and is encoded into
Sat Mar 21 22:47:13 1998 H.J. Lu (hjl@gnu.org)
* opcode/i386.h (i386_optab): Set "lgdt" and "lidt" to use
linear address only with LinearAddress in the "opcode_modifier"
bit.
Index: include/opcode/i386.h
===================================================================
RCS file: /home/work/cvs/gnu/binutils/include/opcode/i386.h,v
retrieving revision 1.20
diff -u -p -r1.20 i386.h
--- include/opcode/i386.h 1997/11/01 03:09:27 1.20
+++ include/opcode/i386.h 1998/03/22 06:25:45
@@ -464,8 +464,8 @@ static const template i386_optab[] = {
/* protection control */
{"arpl", 2, 0x63, _, Modrm, { Reg16, Reg16|Mem, 0} },
{"lar", 2, 0x0f02, _, Modrm|ReverseRegRegmem, { WordReg|Mem, WordReg, 0} },
-{"lgdt", 1, 0x0f01, 2, Modrm, { Mem, 0, 0} },
-{"lidt", 1, 0x0f01, 3, Modrm, { Mem, 0, 0} },
+{"lgdt", 1, 0x0f01, 2, Modrm|LinearAddress, { Mem, 0, 0} },
+{"lidt", 1, 0x0f01, 3, Modrm|LinearAddress, { Mem, 0, 0} },
{"lldt", 1, 0x0f00, 2, Modrm, { WordReg|Mem, 0, 0} },
{"lmsw", 1, 0x0f01, 6, Modrm, { WordReg|Mem, 0, 0} },
{"lsl", 2, 0x0f03, _, Modrm|ReverseRegRegmem, { WordReg|Mem, WordReg, 0} },
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