Re: gcc-8 objtool warnings

From: Josh Poimboeuf
Date: Wed Aug 23 2017 - 12:01:10 EST


On Wed, Aug 23, 2017 at 03:38:02PM +0200, Arnd Bergmann wrote:
> On Wed, Aug 23, 2017 at 2:48 PM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
> > On Wed, Aug 23, 2017 at 02:22:34PM +0200, Arnd Bergmann wrote:
> >> ...
> >>
> >> 0000000000000000 <put_cred_rcu.cold.1>:
> >> 0: e8 00 00 00 00 callq 5 <put_cred_rcu.cold.1+0x5>
> >> 1: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4
> >> 5: 44 8b 8b 64 ff ff ff mov -0x9c(%rbx),%r9d
> >> c: 48 8b 8b 68 ff ff ff mov -0x98(%rbx),%rcx
> >> 13: 44 89 e2 mov %r12d,%edx
> >> 16: 44 8b 83 60 ff ff ff mov -0xa0(%rbx),%r8d
> >> 1d: 4c 89 ee mov %r13,%rsi
> >> 20: 48 c7 c7 00 00 00 00 mov $0x0,%rdi
> >> 23: R_X86_64_32S .rodata.str1.8+0x28
> >> 27: e8 00 00 00 00 callq 2c <__kstrtab_creds_are_invalid+0x3>
> >> 28: R_X86_64_PC32 panic-0x4
> >
> > Thanks. Can you send me one of the .o files?
>
> Attached here now.

Ok, looks like I'll need to add support for this new pattern (jumping to
a .cold section in .text.unlikely).

I'm also about to start work on fixing that other issue you found with
GCC's inefficient update of the stack pointer.

I really appreciate your finding all these warnings (and getting advance
GCC 8 testing). Thanks again!

--
Josh