On Mon, 9 Apr 2001, Rigel wrote:
> All right. I know all about AT&T style syntax, I know many x86 opcodes, but I've never seen this type of addressing mode. This found on line 148 of table.x86 (in the BRK inst.), and looks like this:
> "leal 0x0(%ebp,%ebx,2),%ebp". What's inside the parentheses?
Okay, now I understand the question. That AT&T syntax is such a
pain to digest sometimes. From plowing through my reference material, the
above instruction means:
ebp = ebp + (ebx * 2) + 0
I think that's it, but I'm not positive.
> Got one more. there's a nice little couplet directly before the previous (lines 146,147) that looks like this:
> testl $0xff,%edi
> setz %bl
>
> This sets bl when? is it when edi == 0xff ?
It looks to me like the net effect of the couplet is:
if (!(edi & 0xff))
bl = 1;
The test instruction performs a bitwise 'and' between the 2 operands. Like
a cmp instruction, it discards the result but sets flags. The setz
instruction stores a 1 into the destination if the zero flag is set.
--
-Mike Melanson
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