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.
--
Josh
