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Date: Tue, 07 Jul 2009 10:51:00 -0000
From: Lennyk <lennyk430@gmail.com>
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To: Ian Lance Taylor <iant@google.com>
CC: gcc-help@gcc.gnu.org
Subject: Re: undefined reference to... when using intel inline asm
References: <4A4C69F0.7040201@gmail.com> <m3eisyrhgj.fsf@google.com>	<4A51AA7D.4060809@gmail.com> <m3hbxpn937.fsf@google.com>
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Ian Lance Taylor wrote:
> Lennyk <lennyk430@gmail.com> writes:
>
>   
>> According to the guide - the corresponding GCC translation - should
>> look like this:
>>
>> void bswap(int* n)
>> {
>>    asm("movl       %0, %%eax" : : "g" (*n));
>>    asm("bswap    %eax");
>>    asm("movl      %%eax, %0" : "=g" (*n));
>> }
>>
>> But, for some reason, the result is not a "bswapped" n.
>> Why?
>>     
>
> * What does the generated code look like?
> * You shouldn't break up the asm statements like that--write one asm
>   with three assembler statements.
> * Let the compiler do the data movement for you; it's good at it.
> * If you're going to clobber %eax in an asm, you need to say so
>   explicitly; that's probably why this code sequence is breaking.
>   asm("bswap %%eax" : : : "eax");
>
> Anyhow, I would write it like this:
>
> void bswap(int* n)
> {
>   asm("bswap %0" : "=r" (*n) : "0" (*n));
> }
>
> Ian
>
>   
Thanks Ian!

After going over the GCC-Inline Assembly guides - I think I'm starting 
to get the hang of it.

Thanks for your assistance!