Displacement def in as

Displacement def in as

[A D]

I am a newbie and i have question. What does
displacement mean according to segmented
memory model? Does it mean anything  in terms
of Segment Descriptor? Thanks.

Offset = Base + (Index * Scale) + displacement

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Re: Displacement def in as

[Robert Plantz]

If you are using the gnu assembler, gas, you should
become familiar with the info for it. The command
is
    info as

Go to Machine Dependencies, then i386-Dependent,
then i386-Memory. There you will see that the AT&T
syntax is
    DISP(BASE, INDEX, SCALE)

DISP is an integer. An example is
    movl   $0, -4(%ebp)
which would store 32 bits of zero at the
memory location starting 4 bytes negative
from the address in the ebp register. (This
instruction does not use INDEX or SCALE.)

Linux uses a flat memory model, so you don't
need to worry about the segmentation registers
if you run your program under Linux.


On Wed, 2006-11-22 at 18:44 -0500, A D wrote:
> I am a newbie and i have question. What does
> displacement mean according to segmented
> memory model? Does it mean anything  in terms
> of Segment Descriptor? Thanks.
> 
> Offset = Base + (Index * Scale) + displacement
> 

Re: Displacement def in as

[A D]

>Robert Plantz  wrote:
>If you are using the gnu assembler, gas, you should
>become familiar with the info for it. The command
>is
>     info as
>
>Go to Machine Dependencies, then i386-Dependent,
>then i386-Memory. There you will see that the AT&T
>syntax is
>     DISP(BASE, INDEX, SCALE)
>
>DISP is an integer. An example is
>     movl   $0, -4(%ebp)
>which would store 32 bits of zero at the
>memory location starting 4 bytes negative
>from the address in the ebp register. (This
>instruction does not use INDEX or SCALE.)
>
>Linux uses a flat memory model, so you don't
>need to worry about the segmentation registers
>if you run your program under Linux.

Thank you Robert Plantz for your wonderful insight.

--STeve

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