From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean Delvare Subject: Re: [PATCH] video: limit stack usage of ir-kbd-i2c.c Date: Tue, 26 Feb 2008 23:23:20 +0100 Message-ID: <20080226232320.2df756d6@hyperion.delvare> References: <20080225205055.GA27455@joi> <20080226133222.7af260b2@hyperion.delvare> <20080226210307.GA6085@joi> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20080226210307.GA6085@joi> Sender: linux-kernel-owner@vger.kernel.org To: Marcin Slusarz Cc: LKML , Mauro Carvalho Chehab , i2c@lm-sensors.org, video4linux-list@redhat.com List-Id: linux-i2c@vger.kernel.org Hi Marcin, On Tue, 26 Feb 2008 22:03:16 +0100, Marcin Slusarz wrote: > Do you have an idea (or patch :D) how to solve this: > 0x00000234 v4l_compat_translate_ioctl [v4l1-compat]: 1376 > ? That's on top of my make checkstack output Random ideas (but I am in no way a specialist of this exercise): * You could try moving the structures to the blocks where they are used, in the case a given structure is used for only one ioctl. I'm not too sure how gcc handles local variables declared inside blocks with regards to stack reservation though. I thought it would work but my experiments today seem to suggest it doesn't. * You can move the handling of some ioctls to dedicated functions, just like I did in i2c-dev: http://lists.lm-sensors.org/pipermail/i2c/2008-February/003010.html However there is a risk that gcc will inline these functions (that's what happened to me...) Not sure how to prevent gcc from inlining. * You can allocate the structures dynamically, as you originally wanted to do for ir-kbd-i2c. However this has a performance penalty and will fragment the memory, so it's not ideal. * If each ioctl uses only one of the structures, you may define a union of all the structures. The size of the union will be the size of the biggest structure, so you save a lot of space on the stack. -- Jean Delvare