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

[Robert Plantz <plantz@sonoma.edu>]

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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