flat assembler
Message board for the users of flat assembler.

Index > Main > Cross-platform development & Calling conventions

Author
Thread Post new topic Reply to topic
16bitPM



Joined: 08 Jul 2011
Posts: 28
16bitPM
Hello!

I wrote an assembly-optimized version of a long multiply in 64-bit mode (actually a 256x256-bit multiply modulo a very long number, according to the secp256k1 protocol).
A friend was wondering how this assembly file would withstand cross-platform development. That's to say: the calling conventions between Windows and Linux are different! http://en.wikipedia.org/wiki/X86_calling_conventions#x86-64_calling_conventions.

Now this is very annoying. I'm quite used to MASM style syntax (or its fork JWASM) which COULD provide a solution via prototyping, but apparently the FASTCALL convention has not been implemented for ELF64 yet.
Still, the question remains... because most assemblers don't have this kind of prototyping.
I could also duplicate all code and change it according to the calling convention.
Swapping registers around is no option since that function is called billions of times and is time-critical.
My friend is more a fan of inline assembly in a GCC __asm__ blocks, but as most assembly programmers I have a deep hate towards AT&T style syntax Wink

So the question is... have any of you had experience with this kind of problem before & how to deal with this situation in the best way?
Post 27 Mar 2013, 01:13
View user's profile Send private message Reply with quote
revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17671
Location: In your JS exploiting you and your system
revolution
Are you asking about calling conventions for the OS? Because you are not forced to use the OS API calling convention for your own functions. Especially for time-critical functions where normal rules tend to get thrown out in favour of a more efficient implementation.
Post 27 Mar 2013, 01:39
View user's profile Send private message Visit poster's website Reply with quote
ProphetOfDoom



Joined: 08 Aug 2008
Posts: 120
Location: UK
ProphetOfDoom
I wrote a fasm macro about a year ago that wraps the Linux calling convention. However it's a bit messy, may still have bugs and I can't offer support cos I'm too busy Razz

http://board.flatassembler.net/topic.php?t=14142
Post 27 Mar 2013, 02:47
View user's profile Send private message Reply with quote
16bitPM



Joined: 08 Jul 2011
Posts: 28
16bitPM
revolution wrote:
Are you asking about calling conventions for the OS? Because you are not forced to use the OS API calling convention for your own functions. Especially for time-critical functions where normal rules tend to get thrown out in favour of a more efficient implementation.


The function will be called from a C or C++ program. So, I fear that recompiling the source on Windows will yield another binary which is incompatible because my code assumes the Linux calling convention:

void ExSetMult((uint64_t *) a.n, (uint64_t *) b.n, (uint64_t *) result);

--> Linux: a.n will be in rdi, b.n in rsi and the pointer to the result will be in rdx
--> Windows: rcx, rdi, r8 respectively, *AND* you have to set up a frame



BUT, I may have solved the puzzle already: GCC has modifiers to change its behaviour. So I can prototype the functions in my C header as follows:


Code:
extern "C" void __attribute__ ((sysv_abi)) _ExSetMult(uint64_t *, uint64_t *, uint64_t *);
extern "C" void __attribute__ ((sysv_abi)) _ExSetSquare(uint64_t *, uint64_t *);
    
Post 27 Mar 2013, 12:19
View user's profile Send private message Reply with quote
Display posts from previous:
Post new topic Reply to topic

Jump to:  


< Last Thread | Next Thread >
Forum Rules:
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


Copyright © 1999-2020, Tomasz Grysztar. Also on GitHub, YouTube, Twitter.

Website powered by rwasa.