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SubjectRe: [PATCH] x86/mm: annotate no_context with UNWIND_HINTS
On Mon, Oct 15, 2018 at 07:34:14AM -0700, Andy Lutomirski wrote:
>
>
> > On Oct 14, 2018, at 10:17 PM, Nathan Chancellor <natechancellor@gmail.com> wrote:
> >
> >> On Sun, Oct 14, 2018 at 08:43:18PM -0700, Andy Lutomirski wrote:
> >> On Sun, Oct 14, 2018 at 5:37 PM Nick Desaulniers
> >> <nick.desaulniers@gmail.com> wrote:
> >>>
> >>> Fixes the objtool warning:
> >>> arch/x86/mm/fault.o: warning: objtool: no_context()+0x220: unreachable
> >>> instruction
> >>>
> >>> Link: https://github.com/ClangBuiltLinux/linux/issues/204
> >>> Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
> >>> ---
> >>> arch/x86/mm/fault.c | 6 ++++--
> >>> 1 file changed, 4 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> >>> index 47bebfe6efa7..057d2178fa19 100644
> >>> --- a/arch/x86/mm/fault.c
> >>> +++ b/arch/x86/mm/fault.c
> >>> @@ -760,9 +760,11 @@ no_context(struct pt_regs *regs, unsigned long error_code,
> >>> * and then double-fault, though, because we're likely to
> >>> * break the console driver and lose most of the stack dump.
> >>> */
> >>> - asm volatile ("movq %[stack], %%rsp\n\t"
> >>> + asm volatile (UNWIND_HINT_SAVE
> >>> + "movq %[stack], %%rsp\n\t"
> >>> "call handle_stack_overflow\n\t"
> >>> - "1: jmp 1b"
> >>> + "1: jmp 1b\n\t"
> >>> + UNWIND_HINT_RESTORE
> >>> : ASM_CALL_CONSTRAINT
> >>> : "D" ("kernel stack overflow (page fault)"),
> >>> "S" (regs), "d" (address),
> >>
> >> NAK. Just below this snippet is unreachable();
> >>
> >> Can you reply with objtool -dr output on a problematic fault.o? Josh,
> >> it *looks* like annotate_unreachable() should be doing the right
> >> thing, but something is clearly busted.
> >>
> >> Also, shouldn't compiler-clang.h contain a reasonable definition of
> >> unreachable()?
> >>
> >> --Andy
> >
> > Hi Andy,
> >
> > Did you mean 'objdump -dr'? If so, here you go (rather long, sorry if I
> > should have pasted it here instead):
> > https://gist.github.com/nathanchance/f038bb0a6653b975bb8a4e64fcd5503e
> >
> >
>
> Hmm, -dr wasn’t quite enough to dump the .discard bits, assuming they’re there at all. Can you just put the whole .o file somewhere?

Here you go: https://nathanchance.me/downloads/.tmp/fault.o

Thanks,
Nathan

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