Passing parameters to assembler functions in 'C' 64 style.

Passing parameters to assembler functions in 'C' 64 style.

[£ukasz]

Hi. 
I started to write assembler functions for C on 64-bit arch. On 32-bit arch. every parameters ware put on stack, now is different, what can be easyly seen reading source program. For example if im passing one  
(int *) parameter, adress (&int) is kept in %rdi register, and so one if u are passing more parameters. Ofcurse is not dificult to use it if u know but is there any key according to which parameters are stored?. I've made some "experiments" with different numbers and kind parameters, but the "key" must be described somewhere.

Luke


      

Re: Passing parameters to assembler functions in 'C' 64 style.

[Robert Plantz]

You need the AMD64 Application Binary Interface (v0.99) available at

http://www.x86-64.org/documentation.html

In particular, see Figure 3.4 on page 21.

Pay attention to the use of rax. The default for floating point in
x88-64 is the SSE unit. If a function will accept floating point
arguments (for example, printf) the number of floating point arguments
must be placed in eax. Write a C program that calls printf and use the
-S option to see the assembly language.

A good way to see what the compiler is doing to C code is to use the
following options:
$ gcc -O0 -g -Wa,-adhls -fno-asynchronous-unwind-tables \
> myProg.c > myProg.lst

(I added the "\" here to avoid confusing word wrapping.)

Bob

On Thu, 2008-12-04 at 12:20 -0800, £ukasz wrote:
> Hi. 
> I started to write assembler functions for C on 64-bit arch. On 32-bit arch. every parameters ware put on stack, now is different, what can be easyly seen reading source program. For example if im passing one  
> (int *) parameter, adress (&int) is kept in %rdi register, and so one if u are passing more parameters. Ofcurse is not dificult to use it if u know but is there any key according to which parameters are stored?. I've made some "experiments" with different numbers and kind parameters, but the "key" must be described somewhere.
> 
> Luke


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Re: Passing parameters to assembler functions in 'C' 64 style.

[Frederic Marmond]

Hi Luke,

maybe this document may answer your question:
http://www.x86-64.org/documentation/abi.pdf

Have a particular look to section 3.2

Fred

Le Thursday 04 December 2008 à 21:20, £ukasz a écrit :
> Hi.
> I started to write assembler functions for C on 64-bit arch. On 32-bit
> arch. every parameters ware put on stack, now is different, what can be
> easyly seen reading source program. For example if im passing one (int *)
> parameter, adress (&int) is kept in %rdi register, and so one if u are
> passing more parameters. Ofcurse is not dificult to use it if u know but is
> there any key according to which parameters are stored?. I've made some
> "experiments" with different numbers and kind parameters, but the "key"
> must be described somewhere.
>
> Luke
>
>
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-assembly"
> in the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


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Re: Passing parameters to assembler functions in 'C' 64 style.

[£ukasz]

Thank You for answers. It helps a lot ( of course i chacked what gcc is doing with -S option, but i haven't enough time to chack what compiler would do witch ex. 1000 parameters of different kinds( if there exist some body who would wants to create such function, without using for ex. struc ;)), so i guess that there must be a 'key'). Any way thanks to U i have some clue.

Luke

--- On Thu, 12/4/08, £ukasz <blurrpp@yahoo.com> wrote:

> From: £ukasz <blurrpp@yahoo.com>
> Subject: Passing parameters to assembler functions in 'C' 64 style.
> To: linux-assembly@vger.kernel.org
> Date: Thursday, December 4, 2008, 9:20 PM
> Hi. 
> I started to write assembler functions for C on 64-bit
> arch. On 32-bit arch. every parameters ware put on stack,
> now is different, what can be easyly seen reading source
> program. For example if im passing one  
> (int *) parameter, adress (&int) is kept in %rdi
> register, and so one if u are passing more parameters.
> Ofcurse is not dificult to use it if u know but is there any
> key according to which parameters are stored?. I've made
> some "experiments" with different numbers and kind
> parameters, but the "key" must be described
> somewhere.
> 
> Luke
> 
> 
>       
> --
> To unsubscribe from this list: send the line
> "unsubscribe linux-assembly" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at 
> http://vger.kernel.org/majordomo-info.html


      
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