Re: -current build failure
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On Tue, Jul 24, 2012 at 10:08:13PM +0100, David Chisnall wrote:
> On 23 Jul 2012, at 20:53, David Chisnall wrote:
>=20
> > On 23 Jul 2012, at 20:18, Konstantin Belousov wrote:
> >=20
> >> 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.
> >=20
> > 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:
> >=20
> > http://llvm.org/bugs/show_bug.cgi?id=3D13438
>=20
> And fixed it in LLVM r160687. Since it's a single-line change, we can pr=
obably pull it into our version.
>=20
> dim: http://llvm.org/viewvc/llvm-project?view=3Drev&revision=3D160687
As kan rightfully notes, the assumption that &%fs:0 =3D=3D *%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.
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