Re: __builtin_constant_p and inline assembly constraints

[Simon Kagstrom <simon dot kagstrom at bth dot se>]

At Wed, 23 Aug 2006 11:02:24 +0100,
Andrew Haley wrote:
> 
> Weird.  There's not really enough information here.  Can you provide
> the .s file from the compiler?  That would give us more of a clue.

I've attached it below.

At Wed, 23 Aug 2006 11:14:45 +0100,
Andrew Haley wrote:
> 
> Simon Kagstrom writes:
>  > 
>  > #define _syscall1(type,name,atype,a) \
>  > type name(atype a) { \
>  > 	register unsigned long __v0 asm("$2"); \
>  > 	__asm__ volatile (".set  push\n.set  noreorder\n"); \
>  >         __emit_parameter(a); \
>  > 	__asm__ volatile ( \
>  > 	".short 0xffff\t#" #name "\n\t" \
>  >         ".short %1\n" \
>  > 	: "=&r" (__v0) \
>  > 	: "i" (__NR_##name) ); \
>  >         __asm__ volatile(".set\tpop\n"); \
>  > 	return (type) __v0; \
>  > }
> 
> I'm still trying to get my head around what the assembler will do when
> gcc moves these asms around.
> 
> Put the ".set  push\n.set  noreorder\n" stuff *inside* the asms.  Please.  :-)

I tried placing the .set push / .set noreorder stuff in the
__emit_parameter and the main asm statement, and the generated code
looks better:

 1002314:               addiu   sp,sp,72
 1002318:               0xfffe0009
 100231c:               j       100229c <test_malloc+0x144>
 1002320:               nop

01002324 <main>:
 1002324:               addiu   sp,sp,-24

But I cannot quite understand where the difference comes from. What I
would like the original macro to generate is:

.set push
.set noreorder
	.long	0xfffe0009
	.short	0xffff
	.short	9
.set pop

Is the problem perhaps that GCC outputs assembly directives "between"
the __emit_parameter and the main asm statement without pushing the
current settings?

// Simon

Attachment: main.s
Description: Binary data