function's prologue/epilogue

[devel]

Hi there,

has anybody experiences with implementing prologue/epilogue of function in gcc?
For example to change ret instruction to lret.

regards & thnx in advance,
devel.

[Combuster]

The Good Thing (tm) is to use assembler to wrap up GCC functions for interrupts.

[mathematician]

push ds
push es
push fs
push gs
push ebp
push eax
push ebx
push ecx
push edx
push esi
push edi

call _func

;next three lines for hardware interrupts only
; - assuming you're not using APIC

mov al, 20h
out 20h, al
out 0a0h, al
pop edi
pop esi
pop edx
pop ecx
pop ebx
pop eax
pop ebp
pop gs
pop fs
pop es
pop ds
iret

adjust as necessary for 64 bit mode

[devel]

Sorry for misunderstanding. I meant whether it is possible to override gcc's default
prolog/epilogue code? Is there any macro in gcc for handling this?

regards,
devel.

[JamesM]

No, it can't be done.

At least, when I was looking for a way to do it, I didn't find any.

[XCHG]

I don't know much C but I remember with Visual Studio, I could create naked functions in which I got to write my own prologue and epilogue in pure assembly:

Code: Select all

int __declspec(naked) __stdcall Add (int a, int b){
  __asm{
    PUSH    EBP
    MOV     EBP , ESP
    MOV     EAX , DWORD PTR [EBP + 0x08]
    ADD     EAX , DWORD PTR [EBP + 0x0C]
    POP     EBP
    RET     0x08
  }
}

I don't know but maybe there is a way around it also in GCC.

[blound]

I don't know much C but I remember with Visual Studio, I could create naked functions in which I got to write my own prologue and epilogue in pure assembly:

Code: Select all

int __declspec(naked) __stdcall Add (int a, int b){
  __asm{
    PUSH    EBP
    MOV     EBP , ESP
    MOV     EAX , DWORD PTR [EBP + 0x08]
    ADD     EAX , DWORD PTR [EBP + 0x0C]
    POP     EBP
    RET     0x08
  }
}

I don't know but maybe there is a way around it also in GCC.

From needing "naked" supoprt on another project, gcc only supports naked on some arches ( x86 not being one of them ), I got this from trying it myself, and a partner on the project reading the mailing lists and seeing one of the gcc devs saying "who would need this on x86..." - so it never got implemented

[Brynet-Inc]

I don't see a use to this... considering in such a "naked" function, you couldn't actually "have" any C code, (The compiler couldn't automatically determine the convention you're using.. right?)

So what's the point? Why not just write the entire function in asm?

Just my opinion...