Date: Wed, 25 Jul 2012 01:43:38 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: David Chisnall <theraven@freebsd.org> Cc: Dimitry Andric <dim@freebsd.org>, freebsd-current@freebsd.org, Kim Culhan <w8hdkim@gmail.com> Subject: Re: -current build failure Message-ID: <20120724224338.GZ2676@deviant.kiev.zoral.com.ua> In-Reply-To: <05368BFA-F5F6-49D4-BE63-7C9360E54F54@FreeBSD.org> References: <CAKZxVQV5xhFDN_WbTk-EMoQ18N8u1f4YhqKSJQFUzbX4NZxhUA@mail.gmail.com> <50097BF0.9010103@FreeBSD.org> <CAKZxVQXC6DuX5UTn3goNM9toxSVkP8-7bazTk%2Ba7yLEy7RsJYA@mail.gmail.com> <20120721211628.GE2676@deviant.kiev.zoral.com.ua> <6006581B-6B1C-4DFB-8662-3EB35869CA5F@FreeBSD.org> <20120722180119.GJ2676@deviant.kiev.zoral.com.ua> <20120723191856.GR2676@deviant.kiev.zoral.com.ua> <088BF877-50E6-42C5-98EF-DAB0FA52C348@freebsd.org> <05368BFA-F5F6-49D4-BE63-7C9360E54F54@FreeBSD.org>
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[-- Attachment #1 --] On Tue, Jul 24, 2012 at 10:08:13PM +0100, David Chisnall wrote: > On 23 Jul 2012, at 20:53, David Chisnall wrote: > > > On 23 Jul 2012, at 20:18, Konstantin Belousov wrote: > > > >> Longer description is that pc_curthread is offset 0 if %gs-based. > >> The dereferenced pointer point to the struct thread, which contains > >> td_proc pointer at offset 8. Instead, clang seems to dereference > >> td_proc from offset 8 based on %gs, or something similar. > > > > This appears to be a bug in the LLVM X86 back end. It is performing an invalid fold of the two loads. I have filed this bug: > > > > http://llvm.org/bugs/show_bug.cgi?id=13438 > > And fixed it in LLVM r160687. Since it's a single-line change, we can probably pull it into our version. > > dim: http://llvm.org/viewvc/llvm-project?view=rev&revision=160687 As kan rightfully notes, the assumption that &%fs:0 == *%fs:0 holds for userspace on amd64, and the same is true for %gs userspace on i386. The change you committed to clang/llvm/whatever it called just breaks useful optimization for FreeBSD. Sigh. [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (FreeBSD) iEYEARECAAYFAlAPJRoACgkQC3+MBN1Mb4hxxwCcCK6uhCN5jRilzaMof0VyylQp FOQAn2QaqEwCjnLidV+rYhPdgMfoOGSA =s2V6 -----END PGP SIGNATURE-----help
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