gcc passing parameters

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chorus

Joined: 16 Mar 2004
Posts: 23

chorus 20 Dec 2005, 03:24

Hi all. I'm trying to get a mixed C/ASM project going under linux x86_64. My "problem" is that GCC uses the fastcall calling convention for 64-bit (but not for 32 bit... ??). So my params are coming into asm in rdi,rsi,rdx,rcx, etc. instead of on the stack. Anyone know how to disable "fastcall" in GCC??

And yeah I know it's faster this way... I'd still rather have them on the stack

Thanks for any help
--Chorus

20 Dec 2005, 03:24

RedGhost

Joined: 18 May 2005
Posts: 443
Location: BC, Canada

RedGhost 20 Jan 2006, 02:30

Quote:

GCC can be made to use a register calling convention by compiling with gcc -mregparm=NNN ...
See the GCC documentation for details.

got that from google, so its probably in the GCC readme/doc

_________________
redghost.ca

20 Jan 2006, 02:30

Chewy509

Joined: 19 Jun 2003
Posts: 297
Location: Bris-vegas, Australia

Chewy509 23 Jan 2006, 01:41

gcc on x86-64 (aka AMD64) uses the x86-64 ABI v0.96 for parameter passing by default. IIRC, there is no easy way to tell gcc to use the 32bit ABI (stack based passing) for 64bit apps.

You might want to try one of the gcc newsgroups for further information.

Description:	64bit ABI (remove .txt from end to read)	Download
Filename:	abi-0.96.pdf.txt
Filesize:	334.76 KB
Downloaded:	798 Time(s)

23 Jan 2006, 01:41

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