Re: __asm__ usage??

[Fergus Henderson <fjh at cs dot mu dot oz dot au>]

On 10-Aug-2001, Raghava Raju <vraghava_raju@yahoo.com> wrote:
> hi
> 
>    I want some basic insights into assembly level code
> emmbedded in C language. Following is the code of
> PowerPc ambedded in C languagge:
> 
> unsigned long old,mask, *p;
> 
> 	__asm__ __volatile__(SMP_WMB "\
> 1:	lwarx 	%0,0,%3
> 	andc  	%0,%0,%2
> 	stwcx 	%0,0,%3
> 	bne 	1b"
> 	SMP_MB
> 	: "=&r" (old), "=m" (*p)
> 	: "r" (mask), "r" (p), "m" (*p)
> 	: "cc");
> 
> 	1) what does these things denote: __volatile__,

See the GCC manual (the "Extended Asm" section
of the "C extensions" chapter).

> SMP_WMB, SMP_MB,

They are probably macros defined in the code.

> "r","=&r","=m", "cc"

See the GCC manual (the "Extended Asm" section
of the "C extensions" chapter, and the "Constraints"
section referenced there).

> and 1: .
>           
> 	2) Is it that %0,%2,%3 denote addresses of old,mask,p
> respectively. 

Values of, not addresses of.

>         3) Say if it is PowerPc then how should I
> access registers r1,r2 etc, i.e. what is the exact
> syntax.

Consult the documentation for the PowerPC assembler.

>         5) Some people use "memory" in place of "cc" ,
> like I want to know what are these things.

See the GCC manual.

-- 
Fergus Henderson <fjh@cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.