Re: Inline assembly and ldm/stm

[Marius Groeger <mgroeger at sysgo dot com>]

Hi Bryce,

better late than never..

On Fri, 6 Apr 2007, Bryce Schober wrote:

>    arm_2_registers_t result;
>    __asm__ (
>        "ldmia    %0, {%1,%2}    \n\t"
>        : "+r" (src_addr_ptr), "=r" (result.reg[0]), "=r" ( result.reg[1])
>    );
>    return( result );
> }
> 
> That seems to work fine until the compiler decides to use registers
> for %1 and %2 that aren't in ascending order. I've examined the
> assembly constraints and I don't see anything obvious.

I see two solutions to your problem:

1. you can directly specify two suitable registers in the assembler 
   part. You then also need to list those registers in the clobber list 
   argument of __asm__(). See the gcc info manual, Extended Asm for
   the exact syntax.
   
2. you can use explicit register variables like this:
   register int r1 asm("r1");
   register int r2 asm("r2");

I actually don't know which would be preferable. The second one might be
nicer for long-term maintainance / portability as it is more obvious than
using __asm__'s clobber list.

Regards,
Marius

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Marius Groeger <mgroeger@sysgo.com>
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