Re: objtool crashes with some clang produced .o files

From: Nick Desaulniers
Date: Fri Dec 11 2020 - 19:48:33 EST

On Fri, Dec 11, 2020 at 4:42 PM Nick Desaulniers
<ndesaulniers@xxxxxxxxxx> wrote:
>
> On Fri, Dec 11, 2020 at 12:57 PM Nick Desaulniers
> <ndesaulniers@xxxxxxxxxx> wrote:
> >
> > Thanks for the patch!
> >
> > Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1207
>
> Arnd reported another objtool warning/error from another randconfig in
> https://github.com/ClangBuiltLinux/linux/issues/1209 and CrOS just hit
> this as well.
>
> I haven't been able to isolate the configs yet (Arnd has posted the
> full config: https://pastebin.com/wwwhUL8L
>
> $ ./tools/objtool/objtool orc generate --no-fp --no-unreachable
> --retpoline arch/x86/entry/thunk_64.o
> arch/x86/entry/thunk_64.o: warning: objtool: missing symbol for insn
> at offset 0x3e
>
> Is the offset 0x3e referring to the final `ret` instruction in
> preempt_schedule_notrace_thunk? Observing insn_to_reloc_sym_addend()
> (with your patch applied), it looks like both calls to
> find_symbol_containing() with offset and offset-1 returns NULL. I'm
> curious if there's another quirk going on here, or possibly a config
> from the randconfig that's messing up the special case? I don't follow
> the comment about:
> 119 * Hack alert. This happens when we need to reference
> 120 * the NOP pad insn immediately after the function.
> 121 */
>
> Attached the object file FWIW.

Resending with the attachment renamed; I just got a bounceback from
Josh's mailer daemon.
--
Thanks,
~Nick Desaulniers
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