lkml.org 
[lkml]   [2018]   [Oct]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH] x86/mm: annotate no_context with UNWIND_HINTS
On Mon, Oct 15, 2018 at 8:31 AM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> On Mon, Oct 15, 2018 at 08:22:21AM -0700, Nathan Chancellor wrote:
> > > >>> @@ -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
>
> $ eu-readelf -S /tmp/fault.o |grep reachable
> [12] .discard.reachable PROGBITS 0000000000000000 00002bc0 00000014 0 0 0 1
> [13] .rela.discard.reachable RELA 0000000000000000 00002bd8 00000078 24 I 32 12 8
>
> That confirms that you need a clang version of the unreachable() macro.
>

Duh.

That being said, the generic macro is:

# define unreachable() do { annotate_reachable(); do { } while (1); } while (0)

I'm probably missing some subtlety here, but shouldn't that be
annotate_*un*reachable()?

Of course, there are any number of reasons why there should be a real
definition. Nathan and Nick, does adding something like:

#define unreachable() \
do { \
annotate_unreachable(); \
__builtin_unreachable(); \
} while (0)

to compiler-clang.h fix the problem?

--Andy

\
 
 \ /
  Last update: 2018-10-15 18:05    [W:0.083 / U:0.300 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site