Re: [Qemu-devel] Re: Detecting an assembly instruction in QEMU

["Atif Hashmi" <atifhashmi@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1636 bytes --]

Hi Eduardo,

Thanks a lot for your help. I really appreciate it. I have added the
functionality that I wanted.

By the way, Is there any documentation that can help me better understand
the QEMU source code?

Regards,
Atif

On 4/8/07, Eduardo Felipe <edusaper@gmail.com> wrote:
>
> Hi Atif,
>
> In target-i386/translate.c, there are many variants of mov i.e.
> >  case 0x89: /* mov Gv, Ev */
> >  case 0xc7: /* mov Ev, Iv */
> >  case 0x8b: /* mov Ev, Gv */
> >  case 0x8e: /* mov seg, Gv */
>
>
> That's true. I forgot the fact that mov %eax,%eax can be both:
>
> 0x89 0xC0
> 0x8B 0xC0
>
> It's up to the compiler to choose which one to use.
>
> which one do you think will be called when "mov %eax, %eax" instruction is
> > translated.
> > I printed the value of modrm inside the case 0x89 but the value remains
> > the same whether I use %eax or %ebx.
> >
> > Secondly, How can I extract the source and destination registers from
> > modrm.
>
>
> modrm is the byte following the 0x89 or 0x8B opcode. After
>
> modrm = ldub_code(s->pc++);
>
> you can decode it this way (in binary):
> XXYYYZZZ
>
> XX --> Indexing mode
> YYY --> Destination register
> ZZZ --> Source register
>
> 0xC0 is the value you are looking for 11 000 000 --> (no
> indexing)(%eax)(%eax).
>
> You can find more information here:
> http://pdos.csail.mit.edu/6.828/2005/readings/i386/s17_02.htm
>
> One more thing: you may want to check operand size. It's on "ot" variable,
> and its meaning (from translate.c):
> enum {
>     OT_BYTE = 0,
>     OT_WORD,
>     OT_LONG,
>     OT_QUAD,
> };
>
> being 8, 16, 32 and 64 bits respectively.
>
> Regards,
> Eduardo
>
>

[-- Attachment #2: Type: text/html, Size: 2661 bytes --]