Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 12 Oct 2001 03:59:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 12 Oct 2001 03:59:05 -0400 Received: from trillium-hollow.org ([209.180.166.89]:47621 "EHLO trillium-hollow.org") by vger.kernel.org with ESMTP id ; Fri, 12 Oct 2001 03:58:49 -0400 To: Eric Sandeen cc: linux-xfs@oss.sgi.com, linux-kernel@vger.kernel.org Subject: RH 7.1 gcc 2.96 bug (was Re: TAKE - work around gcc bug during xfs_growfs ) In-Reply-To: Your message of "Thu, 11 Oct 2001 11:59:20 CDT." <3BC5CFE8.84FDB6FC@sgi.com> Date: Fri, 12 Oct 2001 00:59:04 -0700 From: erich@uruk.org Message-Id: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Eric Sandeen wrote: > > You may want to check it against the rawhide -99 version, since you know > > exactly what to test for. If you'd like I could try that tonight for > > you. > > Sure, if you'd like to test it that would be great. I was going to > install that compiler RPM, but it needs a new binutils which needs a > new glibc which needs... :) > > Take a look at that URL for the diff I posted, and back it out. > > To test for the error, ...[example creating an XFS filesystem about 1/2 the partition size, then growing it to the full partition size]... > If you see any errors, it didn't work. :) Well, I wasn't able to reproduce with your test case at all. I suspect that maybe it's the fact that I only had a 2GB spare partition to try it on. On the positive (??!?) side, I looked at the disassembly and found what the compiler is doing wrong in the case you worked around (ok, so you probably already know this, but I'm putting this here so that someone can fix the bug or convince RedHat to move to away from 2.96, maybe to 3.x). In the second one of the 5 cases of where you added a temporary rather than a putting the macro in the function parameter sequence directly, there are some operations done to what appear to be spill locations, but the spill and reload are never performed... so it seems these locations were allocated for spill/reload, but then wires got crossed somewhere. In the "fixed" version, the exact same operations are performed on the same stack locations, but the spill happens before and a reload happens afterward, hence my suspicions. Here is the assembly output difference (from the original and recently "fixed" version of "linux/fs/xfs/xfs_fsops.c" in the linux-xfs CVS tree): "original version": sall %cl, %eax testb $32, %cl cmovne %eax, %edx cmovne %edi, %eax [no spill?!?] --> addl $2, 16(%esp) --> adcl $0, 20(%esp) [no reload!?!] shldl $9, %eax, %edx sall $9, %eax pushl %edx pushl %eax "fixed version": sall %cl, %eax testb $32, %cl cmovne %eax, %edx cmovne %ebx, %eax S-> movl %eax, 8(%esp) --> addl $2, 8(%esp) S-> movl %edx, 12(%esp) --> adcl $0, 12(%esp) pushl $8708 movl 80(%esp), %ecx sall $9, %ecx pushl %ecx R-> movl 16(%esp), %eax R-> movl 20(%esp), %edx shldl $9, %eax, %edx sall $9, %eax pushl %edx pushl %eax Note the ending code sequence to push the parameters on the stack are the same, but in the first sequence, the operations are done on memory locations that have no connection with the rest of the code. Ack. It is very reproducable and happens in all the RedHat 7.1 gcc 2.96 series compiler versions I tried: -81 (the one in the base release), -85 (the one in RedHat's update set), -88, and -99 (the most recent currently in RawHide). Personally, this problem is weird enough to kind of spook me... seems they've had busted register spill/reload logic for a while. The RawHide GCC 3.0.1 compiler I grabbed doesn't have this problem, and the rest of the code in that file appears to be correct regardless of your workaround. Same with "kgcc". Do you want me to send this to RedHat? ...or have you got as good/ better explanation to hand to them already? -- Erich Stefan Boleyn http://www.uruk.org/ "Reality is truly stranger than fiction; Probably why fiction is so popular" - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/