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From: Sri Ram Vemulpali <sri.ram.gmu06@gmail.com>
To: Rajat Sharma <fs.rajat@gmail.com>
Cc: Kernel-newbies <kernelnewbies@nl.linux.org>,
	linux-kernel-mail <linux-kernel@vger.kernel.org>
Subject: Re: Please correct this code
Date: Mon, 31 Jan 2011 15:22:16 -0500	[thread overview]
Message-ID: <AANLkTimXahy8DHKP-g7=A+RDLcEpVk7gHpQvAkuSh3NL@mail.gmail.com> (raw)
In-Reply-To: <AANLkTik76t-BUv0SUMOCBaoiGhH0PKq7cQwM8Q1Lmkei@mail.gmail.com>

thanks for all explanation, it really helped to refine my code

Sri

On Mon, Jan 31, 2011 at 12:58 PM, Rajat Sharma <fs.rajat@gmail.com> wrote:
>> 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@gmail.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@kernelnewbies.org
>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>
>



-- 
Regards,
Sri.

  reply	other threads:[~2011-01-31 20:22 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-31 16:37 Sri Ram Vemulpali
2011-01-31 17:58 ` Rajat Sharma
2011-01-31 20:22   ` Sri Ram Vemulpali [this message]
  -- strict thread matches above, loose matches on Subject: below --
2011-01-31 16:23 Sri Ram Vemulpali

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