Re: [LIP] Intel Opcode Query

On Thu, Jun 10, 2004 at 03:43:09AM -0700, Trideepraj Roychoudhury wrote:
> Hi,
> I am trying to write a disassembler for x86
> processors.

Why not use the existing GNU or BSD disassemblers ?

> Does every opcode that has "one memory operand" needs
> to be "prefixed" with the "Operand-Size/Address-Size
> Prefix" code?

Not every one requires a prefix.

$ cat foo.s
.text

add %eax, %ebx
add %ax, %bx

mov %eax, %ebx
mov %al, %bl

$ objdump -d foo.o

foo.o:     file format elf32-i386

Disassembly of section .text:

00000000 <.text>:
   0:   01 c3                   add    %eax,%ebx
   2:   66 01 c3                add    %ax,%bx
   5:   89 c3                   mov    %eax,%ebx
   7:   88 c3                   mov    %al,%bl

> 
> Otherwise how do I decide which addressing mode to use
> i.e. 16-bit or 32-bit?

You need to look at both the opcode and prefix.

	-Arun


-------------------------------------------------------
This SF.Net email is sponsored by the new InstallShield X.
From Windows to Linux, servers to mobile, InstallShield X is the
one installation-authoring solution that does it all. Learn more and
evaluate today! http://www.installshield.com/Dev2Dev/0504