Messages in this thread | | | Date | Thu, 10 Oct 2013 08:22:38 +0200 | From | Ingo Molnar <> | Subject | Re: [x86] BUG: unable to handle kernel paging request at 00740060 |
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* Jakub Jelinek <jakub@redhat.com> wrote:
> On Wed, Oct 09, 2013 at 09:02:31PM +0200, Peter Zijlstra wrote: > > On Wed, Oct 09, 2013 at 08:16:13PM +0200, Jakub Jelinek wrote: > > > > > Confirmed as gcc bug, filed http://gcc.gnu.org/PR58670 Seems all of > > > 4.[6-9] miscompile it. Will have a look tomorrow unless somebody > > > beats me to it. But historically, the case where asm goto labels > > > jump to fallthru basic block had numerous problems in the past. > > > > That bug lists the component as middle end; this suggests x86_64 would > > be vulnerable too, can you confirm? So far we've only observed the > > wrong code on i386 targets, x86_64 targets appeared correct. > > Any target, the testcase in the bugzilla aborts on x86_64 with -O2, and > even say on ppc64 (sure, one would have to rewrite the asm to have it > fail at runtime).
Please let us know once you know enough about the bug to suggest workarounds. Because it's a nice optimization even extra instruction(s) would be acceptable I suspect: we could perhaps put a NOP into a slowpath, with an (unused) goto to it, or something like that?
Thanks,
Ingo
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