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Message-ID: <AANLkTik76t-BUv0SUMOCBaoiGhH0PKq7cQwM8Q1Lmkei@mail.gmail.com>
Date:	Mon, 31 Jan 2011 23:28:52 +0530
From:	Rajat Sharma <fs.rajat@...il.com>
To:	Sri Ram Vemulpali <sri.ram.gmu06@...il.com>
Cc:	Kernel-newbies <kernelnewbies@...linux.org>,
	linux-kernel-mail <linux-kernel@...r.kernel.org>
Subject: Re: Please correct this code

> Is is not that Code A is wrong, for not mentioning cobbler list
> 'memory' to indicate memory contents are getting updated.
> Please rectify me, if I am wrong.

>From Code B, it looks like instruction to compiler for not using extra
memory location other than ones specified for input param and output
param. Is it some sort of memory synchronization code?

> Also, what does '+m' constraint mean, if I use in inline assembly.

It means the memory location for param is both Readable and Writable

Rajat

On Mon, Jan 31, 2011 at 10:07 PM, Sri Ram Vemulpali
<sri.ram.gmu06@...il.com> wrote:
> Hi,
>
> I have following snippet of code.
>
> Code A
>
> __asm__ __volatile__(
>                     "   lock       ;\n"
>                     "   addl %1,%0 ;\n"
>                     : "=m"  (my_var)
>                     : "ir"  (my_int), "m" (my_var)
>                     :                                 /* no clobber-list */
>                     );
>
> Code B
>
>  __asm__ __volatile__(  "decl %0; sete %1"
>                     : "=m" (my_var), "=q" (cond)
>                     : "m" (my_var)
>                     : "memory"
>                     );
>
> In Code A memory contents are getting updated. And in Code B memory
> contents and 'cond' var are getting updated.
> In Code B in cobbler column 'memory' is used to indicate that this
> code modifies memory contents. But where as in Code A it was not
> mentioned
>
> Is is not that Code A is wrong, for not mentioning cobbler list
> 'memory' to indicate memory contents are getting updated.
> Please rectify me, if I am wrong.
>
> Also, what does '+m' constraint mean, if I use in inline assembly.
> --
> Regards,
> Sri.
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies@...nelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
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