|Summary:||gcc 4.3.0 generates movdqa instructions to non-aligned memory causing crash|
|Product:||[Fedora] Fedora||Reporter:||Stephen Moehle <stephen.moehle>|
|Component:||firefox||Assignee:||Gecko Maintainer <gecko-bugs-nobody>|
|Status:||CLOSED WONTFIX||QA Contact:||Fedora Extras Quality Assurance <extras-qa>|
|Fixed In Version:||Doc Type:||Bug Fix|
|Doc Text:||Story Points:||---|
|Last Closed:||2009-07-14 17:56:46 UTC||Type:||---|
|oVirt Team:||---||RHEL 7.3 requirements from Atomic Host:|
|Cloudforms Team:||---||Target Upstream Version:|
Description Stephen Moehle 2008-05-18 03:26:34 UTC
Description of problem: GCC 4.3.0 generates movdqa instructions referencing non-aligned memory when optimizing with "-O3 -march=core2". The documentation for movdqa says that the mmemory location must be 16-byte aligned, but GCC is only aligning to 8 bytes. The improperly aligned memory location causes a crash. Version-Release number of selected component (if applicable): gcc-4.3.0-8 How reproducible: Always. Steps to Reproduce: Build Firefox 3 trunk with "-O3 -march=core2". The pow5mult routine in jsdtoa.c will be have the bad movdqa instructions, and Firefox will crash on startup. Actual results: Crash! Additional info: Could ensure that memory is properly aligned or could use the movdqu instruction which does not require alignment
Comment 1 Stephen Moehle 2008-05-18 18:55:03 UTC
The assembly in question looks like: movdqa %xmm0, -200(%ebp) movl p5s_lock@GOTOFF(%ebx), %eax movl %eax, (%esp) call PR_Unlock@PLT movl -28(%ebp), %esi movdqa -200(%ebp), %xmm0 It looks like the compiler is trying to preserve the value of %xmm0 across function calls. The offset used by all the examples of this is -200, which is not 16-byte aligned. I should also note that I am running x86 F9.
Comment 2 Jakub Jelinek 2008-05-19 08:37:37 UTC
Then likely firefox is buggy. -200(%ebp) must be 16-byte aligned. The ABI says that %esp should be 16-byte aligned right before the call instruction is executed (i.e. first argument passed on the stack is 16-byte aligned). But the call instruction pushes 4 bytes (the return address) and in the function prologue: pushl %ebp movl %esp, %ebp another 4 bytes are pushed. So, for functions that use frame pointer %ebp is supposed to satisfy ((%ebp + 8) & 15) == 0. Therefore, %ebp - 200 is also 16-byte aligned. AFAIK Firefox contains bridges written in assembly, so that's most likely the place which doesn't honor the ABI and misaligns the stack. To my knowledge all similar issues on the glibc side (e.g. in clone/pthread_create, or makecontext, have been fixed quite some time ago). Should be fairly easy to find out, run it in the debugger, see where the misaligned access is done, and go up through the backtrace, checking whether the stack pointer is aligned properly in each frame, in some lower frames it will be most likely misaligned, in start_thread or main it should be aligned properly. Until that is fixed in firefox, you just can't build firefox with the vectorizer on (enabled at -O3 plus CPU selection for SSE/SSE2 support). OT, -O3 is really meant to be used for performance critical code, if you build a huge app like firefox with -O3, you'll see most likely performance degradation due to much increased cache footprint.
Comment 3 Bug Zapper 2009-06-10 00:57:09 UTC
This message is a reminder that Fedora 9 is nearing its end of life. Approximately 30 (thirty) days from now Fedora will stop maintaining and issuing updates for Fedora 9. It is Fedora's policy to close all bug reports from releases that are no longer maintained. At that time this bug will be closed as WONTFIX if it remains open with a Fedora 'version' of '9'. Package Maintainer: If you wish for this bug to remain open because you plan to fix it in a currently maintained version, simply change the 'version' to a later Fedora version prior to Fedora 9's end of life. Bug Reporter: Thank you for reporting this issue and we are sorry that we may not be able to fix it before Fedora 9 is end of life. If you would still like to see this bug fixed and are able to reproduce it against a later version of Fedora please change the 'version' of this bug to the applicable version. If you are unable to change the version, please add a comment here and someone will do it for you. Although we aim to fix as many bugs as possible during every release's lifetime, sometimes those efforts are overtaken by events. Often a more recent Fedora release includes newer upstream software that fixes bugs or makes them obsolete. The process we are following is described here: http://fedoraproject.org/wiki/BugZappers/HouseKeeping
Comment 4 Bug Zapper 2009-07-14 17:56:46 UTC
Fedora 9 changed to end-of-life (EOL) status on 2009-07-10. Fedora 9 is no longer maintained, which means that it will not receive any further security or bug fix updates. As a result we are closing this bug. If you can reproduce this bug against a currently maintained version of Fedora please feel free to reopen this bug against that version. Thank you for reporting this bug and we are sorry it could not be fixed.