From: James Colannino <james@colannino.org>
To: linux-assembly@vger.kernel.org
Subject: Re: Question about GCC and stack
Date: Mon, 12 Sep 2005 16:15:52 -0700 [thread overview]
Message-ID: <43260C28.6020406@colannino.org> (raw)
In-Reply-To: <17189.59931.532740.834365@eidolon.muppetlabs.com>
Brian Raiter wrote:
>>The subl instruction is pointless, I dont know why it's inserted. It
>>could be just generic stub code that gcc always inserts for
>>allocating stack variables, but as in this case you dont use any, it
>>allocates $0 bytes...I'm sure someone will correct me if there's a
>>good reason for it :)
>>
>>
>
>I expect that the instructions obtained by the original poster were
>created by gcc without optimization. Run gcc with -O2 or so would
>probably yield a simpler set of instructions.
>
>
It was without -O2, but when I used -O2, the code was pretty much the
same. The only difference was that instead of moving the value 0 into
eax, xor eax, eax was used to mask out all the bits (equalling 0, and
I'm assuming that's probably slightly more efficient than moving a value
into a register.) Also, instead of the leave instruction, the ebp and
esp were manipulated manually, I guess because maybe the leave
instruction, like the enter instruction, is slower?
James
--
My blog: http://www.crazydrclaw.com/
My homepage: http://james.colannino.org/
"You can only find truth with logic if you have already found truth without it." --G. K. Chesterton
next prev parent reply other threads:[~2005-09-12 23:15 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-09-12 18:09 Question about GCC and stack Tavis Ormandy
2005-09-12 20:50 ` Brian Raiter
2005-09-12 23:15 ` James Colannino [this message]
2005-09-12 23:13 ` James Colannino
-- strict thread matches above, loose matches on Subject: below --
2005-09-12 6:50 James Colannino
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