Functions in Asm

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denial

Joined: 12 Sep 2004
Posts: 98

denial 27 Nov 2004, 11:27

Hi.

I know how to code procedures, but is it also possible to pass a parameterlist?

like in C:

Code:

int function(char* x, int y, float z){...}

I would like to use something like this in fAsm like the code below, but of course it doens't work that way Wink

But is there a way to do this?

Code:

proc function x rb 50, y dd 0, z dd 0

Thank you

27 Nov 2004, 11:27

roticv

Joined: 19 Jun 2003
Posts: 374
Location: Singapore

roticv 27 Nov 2004, 12:30

char * is a pointer....

it should be

proc function, x, y, z

27 Nov 2004, 12:30

bogdanontanu

Joined: 07 Jan 2004
Posts: 403
Location: Sol. Earth. Europe. Romania. Bucuresti

bogdanontanu 27 Nov 2004, 13:39

in C

Code:

My_Function(param_01,param_02, unsigned long * param_03);

in TASM:

Code:

Call My_Function STDCALL, [param_01],[param_02], offset param_03

you do not need [] arround params if they are scalars: numerical constants, registers etc

in MASM:

Code:

Invoke My_Function, param_01,param_02,addr param_03

in FASM:
there are variouse macros that will allow you to do either:

Code:

Call My_Function,[param_01],[param_02],param_03

or:

Code:

 STDCALL My_Function, [param_01],[param_02],param_03

There are evem more advanced macros in FASM, TASM,MASM that will allow you to do something like this:

Code:

Call My_Function, CSTRING("My first parameter"), Other_Function(other_param),offset param_03

However nice those things might look like... IMHO you should start with the basics like

Code:

push param_01
push param_02
push offset param_03
Call My_Function

And improve in small steeps until you completly understand what you are doing and using...

Also you should understand about ARGUMENTS and LOCAL variables inside functions ... and function PROTOTYPES

There are also variavle numer of parameters lists like :VARARG for both functions and macros

Usually the macro system of assemblers is much more powerfull than the one of C/C++ (a few magnitule levels better)

27 Nov 2004, 13:39

Nikolay Petrov

Joined: 22 Apr 2004
Posts: 101
Location: Bulgaria

Nikolay Petrov 27 Nov 2004, 17:35

if you interest how translate "C" program of assembler use free bcc32 borland compiler with option "-S", when you compiled "C" or "C++" file - this option generate assempler file with detailed comment. In Windows - header "C" function you will "invoke" from crtdll.dll or msvcrt.dll

27 Nov 2004, 17:35

gunblade

Joined: 19 Feb 2004
Posts: 209

gunblade 28 Nov 2004, 01:12

bogdanontanu, shouldnt that be:

Code:

push offset param_03
push param_02
push param_01
call My_Function

(as parameters require to be pushed in reverse order)

gunblade

28 Nov 2004, 01:12

denial

Joined: 12 Sep 2004
Posts: 98

denial 29 Nov 2004, 18:33

thank your for all your replys Smile

29 Nov 2004, 18:33

LiuJunfeng

Joined: 28 Nov 2003
Posts: 48
Location: China

LiuJunfeng 01 Dec 2004, 12:55

I think you are asking how to define a function in fasm, not how to call a function defined in C.

The code in a function starts like this:

Code:

MyFunc:
  push ebp
  mov ebp, esp  ; use ebp as the frame pointer

Then push callee save registers to be used and allocate memory on stack for local variables.

Use [ebp+8],[ebp+12]...to access parameters passed to function.

01 Dec 2004, 12:55

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 01 Dec 2004, 15:07

and ends with

Code:

mov esp,ebp
pop ebp

like, C's

Code:

int MyFunc(int a,int b)
{
  int loc1,loc2 ;local variables
  return 0
}

in asm

Code:

MyFunc:
label b dword at ebp+8
label a dword at ebp+12
label loc1 dword at ebp-4
label loc2 dword at ebp-8
push ebp
mov ebp,esp
sub esp,8 ;8 is size of local variables
... code ...
mov esp,ebp
pop ebp
retn

this is low-level structure of procedure. However you can use FASM's standard "proc" macros to have less typing and have few more abilities (like if you don't use procedure anywhere, then it won't be defined, so you'll save some space in executable).

01 Dec 2004, 15:07

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