From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262490AbVF2KHL (ORCPT ); Wed, 29 Jun 2005 06:07:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262492AbVF2KHL (ORCPT ); Wed, 29 Jun 2005 06:07:11 -0400 Received: from smtp-vbr12.xs4all.nl ([194.109.24.32]:27659 "EHLO smtp-vbr12.xs4all.nl") by vger.kernel.org with ESMTP id S262490AbVF2KG7 (ORCPT ); Wed, 29 Jun 2005 06:06:59 -0400 Message-ID: <8824.192.87.1.200.1120039619.squirrel@192.87.1.200> In-Reply-To: <20050629083452.GC3771@in.ibm.com> References: <20050624200916.GJ6656@stusta.de> <20050624132826.4cdfb63c.akpm@osdl.org> <20050627132941.GD3764@in.ibm.com> <20050627140029.GB29121@nevyn.them.org> <20050628045111.GB4296@in.ibm.com> <20050628112412.GB5652@in.ibm.com> <200506281959.j5SJxaeM022138@elgar.sibelius.xs4all.nl> <20050629083452.GC3771@in.ibm.com> Date: Wed, 29 Jun 2005 12:06:59 +0200 (CEST) Subject: Re: [Fastboot] Re: [-mm patch] i386: enable REGPARM by default From: "Mark Kettenis" To: vgoyal@in.ibm.com Cc: gdb@sources.redhat.com, dan@debian.org, fastboot@lists.osdl.org, linux-kernel@vger.kernel.org, akpm@osdl.org, bunk@stusta.de, alexn@dsv.su.se User-Agent: SquirrelMail/1.4.3a X-Mailer: SquirrelMail/1.4.3a MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > On Tue, Jun 28, 2005 at 09:59:36PM +0200, Mark Kettenis wrote: >> Date: Tue, 28 Jun 2005 16:54:12 +0530 >> From: Vivek Goyal >> >> > Thanks. Any idea what might be amiss with my case where I am not >> seeing >> > proper function parameter values while analyzing kdump generated >> crash >> > dump with gdb. I am using following gdb and gcc versions. >> > >> > GNU gdb Red Hat Linux (6.1post-1.20040607.62rh) >> > gcc (GCC) 3.4.3 20041212 (Red Hat 3.4.3-9.EL4) >> > >> >> Some more info. I dumped the stack contents and it seems that stack >> is fine >> and parameters are intact on stack. So now it seems to be a matter of >> how gdb is interpreting the stack contents. Any guess, what the >> problem is? >> >> I'd say the problem is with a user building stuff with non-standard >> "optimizations", probably even stripping his executable, and expecting >> to be able to debug the result. >> >> Why func2() and func1() are not showing right parameter values. >> > > > In this case I am building linux kernel with debug info (-g) and -mregparm > is not specified. So parameters should be passed on stack. Following > is the effective command line to build kernel/sysfs.c. I am not sure if > any of the below mentioned options are going to affect the gdb results. > > gcc -m32 -Wp,-MD,kernel/.ksysfs.o.d -nostdinc -isystem > /usr/lib/gcc/i386-redhat-linux/3.4.3/include -D__KERNEL__ -Iinclude > -Wall -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing > -fno-common -ffreestanding -O2 -fomit-frame-pointer -g -pipe > -msoft-float -mpreferred-stack-boundary=2 -fno-unit-at-a-time > -march=i686 -mtune=pentium4 -Iinclude/asm-i386/mach-default > -Wdeclaration-after-statement -DKBUILD_BASENAME=ksysfs > -DKBUILD_MODNAME=ksysfs -c -o kernel/ksysfs.o kernel/ksysfs.c -O2 will have some effect. The compiler might optimize away variables (including function arguments) and doesn't always record that fact in the debug information. But the real killer here is probably -fomit-frame-pointer. Last time I looked GCC didn't generate the correct debug information in that case. I didn't really look into this, but it seemed as if GCC blindly produces location descriptions relative to the frame pointer even though there no longer is a frame pointer. GCC 4.0 or 4.1 might have this fixed. > >> Repeating what Daniel said before, by using "regparm", function >> arguments are now passed in registers instead of on the stack. It's >> extremely unlikely that these function arguments will stay in those >> registers for ever, especially since you've only got a handfull of >> them on the i386. > > Sorry for the confusion. In the last mail all the results were reported > with REGPARM disabled. I wanted to make sure that first normal case works > fine and then discuss the REGPARM case later. If you're prepared to do some more tests, you might want to check out what happens if you leave out -O2 and -fomit-frame-pointer, and then add back only -O2 Mark