Re: objtool segfault with ORC unwinder enabled

Josh Poimboeuf
2018-01-03T13:59:29Z

On Wed, Jan 03, 2018 at 01:22:07PM +0100, Markus wrote:
> On Wed, Jan 03, 2018 at 12:19:41 CET Greg Kroah-Hartman wrote:
> > On Wed, Jan 03, 2018 at 11:49:08AM +0100, Markus wrote:
> > > Hello!
> > >
> > > ORC unwinder is enabled in stable for wider testing but still at least one
> > > bug is open:
> > > https://bugzilla.kernel.org/show_bug.cgi?id=197035
> >
> > Random web links on mailing lists don't help much, please put the
> > information here in the email.
>
> Its not a random web link. Its the official kernel.org bugtracker. But nobody
> seems to be looking at it.
>
> > > objtool will segfault because a NULL pointer is dereferenced.
> >
> > And how are you reproducing this?
>
> Just building the kernel with ORC enabled.
> (At least for me. Using framepointers compiles, enabling ORC again breaks it.)
> gcc 6.4.0 (In bug report others were tested as well.)
> elfutils 0.170
> What else may be interesting?
>
> > > Is a NULL pointer sym valid?
> > > If a NULL pointer is invalid, it has to be checked why it is sometimes
> > > NULL.
> > What .config is triggering this problem?
> See attachment.
>
> > And does this show up on 4.14.11, and 4.15-rc6?
> Both: yes.
>
> /tools/objtool/objtool orc generate --no-fp "arch/x86/kernel/irq.o"
>
> => segfault.
>
> Changing CFLAGS for objtool to O1 and starting from gdb:
>
> (gdb) r orc generate --no-fp "arch/x86/kernel/irq.o"
> Starting program: tools/objtool/objtool orc generate --no-fp "arch/x86/kernel/
> irq.o"
>
> Program received signal SIGSEGV, Segmentation fault.
> 0x000055555555e06c in elf_rebuild_rela_section (sec=sec@entry=0x7ffff690d010)
> at elf.c:554
> 554 relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela-
> >type);
> (gdb) bt
> #0 0x000055555555e06c in elf_rebuild_rela_section
> (sec=sec@entry=0x7ffff690d010) at elf.c:554
> #1 0x000055555555d0aa in create_orc_sections (file=file@entry=0x7ffffff7d740)
> at orc_gen.c:210
> #2 0x000055555555c146 in check (_objname=<optimized out>, _no_fp=<optimized
> out>, no_unreachable=<optimized out>, orc=orc@entry=true) at check.c:1971
> #3 0x000055555555811f in cmd_orc (argc=<optimized out>, argv=0x7fffffffd8d8)
> at builtin-orc.c:54
> #4 0x000055555555f490 in handle_internal_command (argv=0x7fffffffd8d0,
> argc=4) at objtool.c:108
> #5 main (argc=4, argv=0x7fffffffd8d0) at objtool.c:131
> (gdb) p rela->sym
> $1 = (struct symbol *) 0x0

Hi Markus,

I'm unable to recreate. Can you attach one of the .o files (like the
above irq.o)?

--
Josh