linux-kernel - Re: [PATCH 2/9] objtool: Fix ORC unwinding in non-JIT BPF generated code

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Date:   Thu, 13 Jun 2019 13:57:11 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Song Liu <songliubraving@...com>,
        Kairui Song <kasong@...hat.com>
Subject: Re: [PATCH 2/9] objtool: Fix ORC unwinding in non-JIT BPF generated
 code

On Thu, Jun 13, 2019 at 08:20:59AM -0500, Josh Poimboeuf wrote:
> Objtool currently ignores ___bpf_prog_run() because it doesn't
> understand the jump table.  This results in the ORC unwinder not being
> able to unwind through non-JIT BPF code.
> 
> Luckily, the BPF jump table resembles a GCC switch jump table, which
> objtool already knows how to read.
> 
> Add generic support for reading any static local jump table array named
> "jump_table", and rename the BPF variable accordingly, so objtool can
> generate ORC data for ___bpf_prog_run().
> 
> 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>
> ---
>  kernel/bpf/core.c     |  5 ++---
>  tools/objtool/check.c | 16 ++++++++++++++--
>  2 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 7c473f208a10..aa546ef7dbdc 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -1299,7 +1299,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
>  {
>  #define BPF_INSN_2_LBL(x, y)    [BPF_##x | BPF_##y] = &&x##_##y
>  #define BPF_INSN_3_LBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = &&x##_##y##_##z
> -	static const void *jumptable[256] = {
> +	static const void *jump_table[256] = {

Nack to the change like above and to patches 8 and 9.
Everyone has different stylistic preferences.
My preference is to keep things as they are.

Please respin the rest. We'll take it via bpf tree.