On Mon, Oct 15, 2018 at 9:03 AM Andy Lutomirski <l...@amacapital.net> wrote:
>
> On Mon, Oct 15, 2018 at 8:31 AM Josh Poimboeuf <jpoim...@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?
I broke this myself in commit 815f0ddb346c
("include/linux/compiler*.h: make compiler-*.h mutually exclusive").
Thanks for the suggestion, will verify then send a patch with your
suggested by tag. Thanks everyone for helping us sort this out!
