From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcin Slusarz Subject: Re: [PATCH] video: limit stack usage of ir-kbd-i2c.c Date: Wed, 27 Feb 2008 11:23:26 +0100 Message-ID: <20080227102309.GA6698@joi> References: <20080225205055.GA27455@joi> <20080226133222.7af260b2@hyperion.delvare> <20080226210307.GA6085@joi> <20080226232320.2df756d6@hyperion.delvare> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20080226232320.2df756d6@hyperion.delvare> Sender: linux-kernel-owner@vger.kernel.org To: Jean Delvare Cc: LKML , Mauro Carvalho Chehab , i2c@lm-sensors.org, video4linux-list@redhat.com List-Id: linux-i2c@vger.kernel.org On Tue, Feb 26, 2008 at 11:23:20PM +0100, Jean Delvare wrote: > Hi Marcin, Hi > 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. That won't work. Variables at beginning of function take only ~600 bytes, so the rest must be from inner blocks and inlines (probably). > * 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. There's "noinline" attribute in linux/compiler.h (compiler-gcc.h actually) for these situations. > * 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. Nice idea. I'll try 2nd and 4th approaches. Marcin Slusarz