Can i call ASM file from my C file

[Willow]

i what to call a ASM file from my kernel.c beacause i make a kernel.c and i make some module like detecting floppy and stuf like that !!!!!!
Email me at: [email protected]


thanck!!!

[sysfree]

of course you can.

[Whatever5k]

I suppose you want to call a assembler *function* within a C function...
Well, that's no problem at all:

Code: Select all

; setup.asm

_asmFunction:
  blabla
  .
  .
  blabla
  ret ; return to caller

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/* kernel.c */
void asmFunction(void);

void kmain(void)
{
.
.
.
asmFunction(); /* call the asm function without parameters */
.
.
.
}

That's it...

[Pype.Clicker]

just a few things that might be useful:
- in most assemblers, you must declare a symbol to be GLOBAL so that you can access it from out there.

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 global _asmFunction 

- DOS-based C compilers prepend a "_" to their symbols, so main() is actually called _main at the assembler level. this is *not* the case under Linux, (thus if you're under linux, you should call your function "asmFunction" rather than "_asmFunction"
- your C code will expect some registers to be modified (eax, edx and maybe edi ... can't remember) while others are expected to be saved/restored (ebx, ebp, ecx, and all the segment registers)
- arguments are pushed on the stack as dwords (hum, i suggest you don't use structure as arguments to a asm function), so provided that you did

Code: Select all

push ebp
mov ebp, esp

you can access the first argument with [ebp+8], the second one with [ebp+12] (i assume 32-bits mode. in 16 bits it would be [bp+4] and [bp+6])

[Whatever5k]

I think the underscore (_) is not needed for ELF...nothing to do with Linux/Windows, or am I wrong?

[Pype.Clicker]

I think the underscore (_) is not needed for ELF...nothing to do with Linux/Windows, or am I wrong?

just the fact that ELF is the binary file in Linux and COFF/PE the binary file in Windows&DOS ...

[Whatever5k]

Yes, so actually, we're both right