Abort x86 assemble code

Abort x86 assemble code

[hugang]

Hello all
	
	I have following code ,and I can not understand the mark line,who can tell me.thanks.
--------------------------------------------------------------
00000eb8 movb   (%ebx),%al      <<IMPORTANT 1-4>>
00000eba incl   %ebx
00000ebb movl   %edi,%ecx
00000ebd shrl   $0x8,%ecx
00000ec0 movl   %edi,%edx
00000ec2 xorb   %dl,%al
00000ec4 movzbl %al,%eax
00000ec7 xorl   0x400dec(,%eax,4),%ecx					????<-----------------What it to do.
00000ece movl   %ecx,%edi
00000ed0 movl   %esi,%eax               <-- jmp here
00000ed2 decl   %esi
00000ed3 orl    %eax,%eax
00000ed5 jne    00000eb8
00000ed7 movl   %edi,0x406894           <- 1-4 see here
00000edd popl   %esi
00000ede popl   %edi
00000edf popl   %ebx

________________________________________________________________
thanks .

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Re: Abort x86 assemble code

[Darryl Miles]

hugang <linuxbest@sina.com> wrote:
>	I have following code ,and I can not understand the mark line,who can tell me.thanks.
> 00000ec7 xorl   0x400dec(,%eax,4),%ecx		????<-----------------What it to do.

extern u_int32_t eax;
extern u_int32_t ecx;

{
	u_int32_t *ptr;

	ptr = (u_int32_t *)((eax * 4) + 0x400dec);

	ecx ^= *ptr;
}


Commonly used in the above form (with a fixed displacement) to access a
32bit value within an array of 32bit values.

The array start offset would be hardwired at 0x400dec, the zero based
index into the array is provided by eax.


-- 
Darryl Miles
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