Re: CVS commit: src/sys/arch

[Maxime Villard <max%m00nbsd.net@localhost>]

Le 14/11/2017 à 15:15, Joerg Sonnenberger a écrit :
> On Tue, Nov 14, 2017 at 03:06:00PM +0100, Maxime Villard wrote:
> > Le 11/11/2017 à 10:10, Manuel Bouyer a écrit :
> > > Module Name:	src
> > > Committed By:	bouyer
> > > Date:		Sat Nov 11 09:10:19 UTC 2017
> > >
> > > Modified Files:
> > > 	src/sys/arch/x86/x86: cpu.c fpu.c identcpu.c
> > > 	src/sys/arch/xen/x86: cpu.c
> > >
> > > Log Message:
> > > Revert http://mail-index.netbsd.org/source-changes/2017/11/08/msg089525.html,
> > > it breaks Xen:
> > > http://www-soc.lip6.fr/~bouyer/NetBSD-tests/xen/HEAD/amd64/201711082340Z_anita.txt
> > >
> > >
> > > To generate a diff of this commit:
> > > cvs rdiff -u -r1.139 -r1.140 src/sys/arch/x86/x86/cpu.c
> > > cvs rdiff -u -r1.25 -r1.26 src/sys/arch/x86/x86/fpu.c
> > > cvs rdiff -u -r1.65 -r1.66 src/sys/arch/x86/x86/identcpu.c
> > > cvs rdiff -u -r1.114 -r1.115 src/sys/arch/xen/x86/cpu.c
> > >
> > > Please note that diffs are not public domain; they are subject to the
> > > copyright notices on the relevant files.
> >
> > You have %rdi = 0xffffa0000c194c18, so the stack is not aligned to 64 bytes,
> > and that's why fxsave faults. Looks like you are triggering another bug earlier
> > in the boot procedure - on my dom0-amd64 fxsave worked correctly.
>
> The stack on AMD64 is not 64byte aligned, but depending on when exactly
> you check, 16byte aligned with or without an offset of 8byte.

GCC assumes 16byte alignment, and pushes __aligned(64) variables following
this assumption. The fact that we end up with a non-aligned value being passed
to fxsave means this assumption was broken at some point earlier - as if we
had done a "jmp label" instead of "callq label" which pushed %rbp but no %rip,
leading to a 8byte offset as you said.