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SubjectRe: [PATCH 1/1] x86/vdso: fix a reference to a non-existing instruction

* Andy Lutomirski <luto@amacapital.net> wrote:

> On Thu, Mar 5, 2015 at 12:13 AM, Jiri Slaby <jslaby@suse.cz> wrote:
> > .LSTARTFDEDLSI1 says:
> > /* HACK: The dwarf2 unwind routines will subtract 1 from the
> > return address to get an address in the middle of the
> > presumed call instruction. Since we didn't get here via
> > a call, we need to include the nop before the real start
> > to make up for it. */
> > .long .LSTART_sigreturn-1-. /* PC-relative start address */
> >
> > But commit 69d0627a7f6e891189124d784d2fa90cae7c449a (x86 vDSO: reorder
> > vdso32 code) from 2.6.25 replaced
> > .org __kernel_vsyscall+32,0x90
> > by ALIGN right before __kernel_sigreturn. Of course, ALIGN need not
> > generate any nop in there. Esp. gcc5 collapses vclock_gettime.o and
> > int80.o together with no generated nops as "ALIGN". In that case
> > kernel does not even link:
> > ld: .eh_frame_hdr table[4] FDE at 0000000000000648 overlaps table[5] FDE at 0000000000000670.
> >
> > So fix this by adding there at least a single nop and make the
> > function ALIGN possibly with more nops then.
> >
> > Kudos for reporting and diagnosing should go to Richard.
> >
> > Signed-off-by: Jiri Slaby <jslaby@suse.cz>
> > Reported-by: Richard Biener <rguenther@suse.de>
> > Cc: stable@vger.kernel.org
> > Cc: Andy Lutomirski <luto@amacapital.net>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > Cc: x86@kernel.org
> > ---
> > arch/x86/vdso/vdso32/sigreturn.S | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/x86/vdso/vdso32/sigreturn.S b/arch/x86/vdso/vdso32/sigreturn.S
> > index 31776d0efc8c..d7ec4e251c0a 100644
> > --- a/arch/x86/vdso/vdso32/sigreturn.S
> > +++ b/arch/x86/vdso/vdso32/sigreturn.S
> > @@ -17,6 +17,7 @@
> > .text
> > .globl __kernel_sigreturn
> > .type __kernel_sigreturn,@function
> > + nop /* this guy is needed for .LSTARTFDEDLSI1 below (watch for HACK) */
> > ALIGN
> > __kernel_sigreturn:
> > .LSTART_sigreturn:
>
> Acked-by: Andy Lutomirski <luto@amacapital.net>
>
> Ingo or Thomas, can you apply this to tip:x86/urgent for this weekend?

Sure, I've applied it.

> Are we willing to depend on cfi-capable assemblers for 32-bit? If
> so, could we rewrite this garbage with .cfi directives? The current
> code is incomprehensible.

We could try, that code is certainly a mess. How much does that
restrict our build compatibility?

Thanks,

Ingo


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