Re: Problem with "mov" in GNU GAS

On Mar 26, 6:49_am, "Rod Pemberton"  <spamt...@crayne.org> wrote:
> "junkoi" <spamt...@crayne.org> wrote in message
>
> news:94d18289-183c-4a52-9770-48fa230d2943@i12g2000prf.googlegroups.com...
>
>
> 
> 
> 
> 
> 
>
> I don't think it's critical, but I'm assuming the var is in a ".data"
> section.
>
> Yes, they are functionally equivalent. _"movl var,ecx" will mov the value 
at
> var's address into ecx, i.e., 0xf1234. _If you wanted to mov the address o
f
> var into ecx [like another responder claimed you were doing...], that'd be
> "movl $var,ecx".
>
> Are you linking the .o file? _If not, a zero (0) value placeholder for the
> memory address will be in the .o code for "movl var, %ecx". _The placehold
er
> is not filled in with the address of var until linked using "ld". _Then, t
he
> code should be functionally equivalent. _Is this the problem? _Typically, 
ld
> is used like this, after assembled with AS or GCC:
>
> _ ld --oformat binary --Ttext 0x7C00 -o mybootcode.bin mybootcode.o
>
> Although very unlikely, you might need to adjust the address size or
> segment:
>
> _ addr32 movl var, %ecx
> _ movl %es:var, %ecx
>
> You can use these for mixed code:
>
> .code16gcc
> .code16
> .code32
> .code64
> .data
> .text
> .att_syntax
> .intel_syntax
> data16 _- operand size override
> data32 _- operand size override
> addr16 _- address size override
> addr32 _- address size override
>
> Let us know...
>
> Rod Pemberton

Thank you, Rod. Your post gave me some hints, and I solved my
problem.

Actually I want to move the value of "var" to %ecx, not its address.
And "var" is in .code section, not .data. So I fixed my code with:

movl %cs:var, %ecx            // i.e movl $0xf1234, %ecx

and it works now, as expected.

Thanks a lot, folks!

Best,
J