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

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Date:   Sat, 6 Jul 2019 22:29:42 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     bp@...en8.de, hpa@...or.com, jpoimboe@...hat.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
Cc:     linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] bpf: Fix ORC unwinding in non-JIT BPF code


* 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

Thanks,

	Ingo