From: Jakub Jelinek <firstname.lastname@example.org> To: email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org Cc: email@example.com Subject: Re: [tip:x86/urgent] compiler/gcc4: Make quirk for asm_volatile_goto( ) unconditional Date: Thu, 13 Feb 2014 12:55:52 +0100 [thread overview] Message-ID: <20140213115552.GU20378@tucnak.redhat.com> (raw) In-Reply-To: <firstname.lastname@example.org> On Thu, Feb 13, 2014 at 03:37:08AM -0800, tip-bot for Steven Noonan wrote: > Commit-ID: a9f180345f5378ac87d80ed0bea55ba421d83859 > Gitweb: http://git.kernel.org/tip/a9f180345f5378ac87d80ed0bea55ba421d83859 > Author: Steven Noonan <email@example.com> > AuthorDate: Wed, 12 Feb 2014 23:01:07 -0800 > Committer: Ingo Molnar <firstname.lastname@example.org> > CommitDate: Thu, 13 Feb 2014 12:34:05 +0100 > > compiler/gcc4: Make quirk for asm_volatile_goto() unconditional > > I started noticing problems with KVM guest destruction on Linux > 3.12+, where guest memory wasn't being cleaned up. I bisected it > down to the commit introducing the new 'asm goto'-based atomics, > and found this quirk was later applied to those. > > Unfortunately, even with GCC 4.8.2 (which ostensibly fixed the > known 'asm goto' bug) I am still getting some kind of > miscompilation. If I enable the asm_volatile_goto quirk for my > compiler, KVM guests are destroyed correctly and the memory is > cleaned up. BTW, which exact 4.8.2 were you using? The last known asm goto bug has been fixed on October, 10th, 2013: http://gcc.gnu.org/PR58670 so before the October, 16th, 2013 4.8.2 release. But already since May 31th, 2013 the tip of the 4.8 GCC branch has been announcing itself as 4.8.2 prerelease. While some distribution versions of GCC announce themselves as the new version only starting from the release date, i.e. snapshots in between 4.8.1 release and 4.8.2 release announce themselves as 4.8.1, in other distributions or upstream it announces itself as 4.8.2. So, if you are using the latter and a snapshot in between May 31th, 2013 and October, 10th, 2013, then you could see gcc patchlevel 2, yet have a gcc with that bug unfixed. So, if the kernel doesn't use a runtime test/configure test to check for this issue, but instead just relies on the patchlevel version, the only safe way would be to look for GCC >= 4.9 or GCC 4.8 with patchlevel > 2 rather than > 1. Jakub
next prev parent reply other threads:[~2014-02-13 11:56 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-10-12 17:10 [GIT PULL] compiler/gcc4: Add quirk for 'asm goto' miscompilation bug Ingo Molnar 2014-02-13 3:09 ` Steven Noonan 2014-02-13 4:11 ` Linus Torvalds 2014-02-13 4:53 ` [PATCH] compiler/gcc4: make quirk for asm_volatile_goto unconditional Steven Noonan 2014-02-13 6:48 ` Mike Galbraith 2014-02-13 7:01 ` [PATCH v2] " Steven Noonan 2014-02-13 11:37 ` [tip:x86/urgent] compiler/gcc4: Make quirk for asm_volatile_goto( ) unconditional tip-bot for Steven Noonan 2014-02-13 11:55 ` Jakub Jelinek [this message] 2014-02-13 13:44 ` Steven Noonan 2014-07-10 15:00 ` Vlastimil Babka 2014-02-13 7:48 ` [GIT PULL] compiler/gcc4: Add quirk for 'asm goto' miscompilation bug Jakub Jelinek 2014-02-13 9:43 ` Ingo Molnar
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