linux-kernel - Re: [tip:x86/urgent] bpf: Fix ORC unwinding in non-JIT BPF code

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Date:   Sat, 6 Jul 2019 20:32:06 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     bp@...en8.de, hpa@...or.com, songliubraving@...com,
        tglx@...utronix.de, rostedt@...dmis.org, kasong@...hat.com,
        daniel@...earbox.net, ast@...nel.org, peterz@...radead.org,
        linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] bpf: Fix ORC unwinding in non-JIT BPF code

On Sat, Jul 06, 2019 at 10:29:42PM +0200, Ingo Molnar wrote:
> 
> * tip-bot for Josh Poimboeuf <tipbot@...or.com> wrote:
> 
> > Commit-ID:  b22cf36c189f31883ad0238a69ccf82aa1f3b16b
> > Gitweb:     https://git.kernel.org/tip/b22cf36c189f31883ad0238a69ccf82aa1f3b16b
> > Author:     Josh Poimboeuf <jpoimboe@...hat.com>
> > AuthorDate: Thu, 27 Jun 2019 20:50:47 -0500
> > Committer:  Thomas Gleixner <tglx@...utronix.de>
> > CommitDate: Sat, 29 Jun 2019 07:55:14 +0200
> > 
> > bpf: Fix ORC unwinding in non-JIT BPF code
> > 
> > Objtool previously ignored ___bpf_prog_run() because it didn't understand
> > the jump table.  This resulted in the ORC unwinder not being able to unwind
> > through non-JIT BPF code.
> > 
> > Now that objtool knows how to read jump tables, remove the whitelist and
> > annotate the jump table so objtool can recognize it.
> > 
> > Also add an additional "const" to the jump table definition to clarify that
> > the text pointers are constant.  Otherwise GCC sets the section writable
> > flag and the assembler spits out warnings.
> > 
> > Fixes: d15d356887e7 ("perf/x86: Make perf callchains work without CONFIG_FRAME_POINTER")
> > Reported-by: Song Liu <songliubraving@...com>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > Acked-by: Alexei Starovoitov <ast@...nel.org>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Kairui Song <kasong@...hat.com>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: Daniel Borkmann <daniel@...earbox.net>
> > Link: https://lkml.kernel.org/r/881939122b88f32be4c374d248c09d7527a87e35.1561685471.git.jpoimboe@redhat.com
> > 
> > ---
> >  kernel/bpf/core.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> Hm, I get this new build warning on x86-64 defconfig-ish kernels plus 
> these enabled:
> 
>  CONFIG_BPF=y
>  CONFIG_BPF_JIT=y
> 
> kernel/bpf/core.o: warning: objtool: ___bpf_prog_run()+0x8da: sibling call from callable instruction with modified stack frame

I assume you have CONFIG_RETPOLINE disabled?  For some reason that
causes GCC to add 166 indirect jumps to that function, which is giving
objtool trouble.  Looking into it.

-- 
Josh