linux-kernel - Re: [PATCH v3 3/4] bpf: Fix ORC unwinding in non-JIT BPF code

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Message-ID: <CAADnVQL2z4BPUvtem-1C_JxzSgc_L8ED=VjGLu7ypPSq3wwC4w@mail.gmail.com>
Date:   Wed, 26 Jun 2019 17:57:08 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Song Liu <songliubraving@...com>,
        Kairui Song <kasong@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v3 3/4] bpf: Fix ORC unwinding in non-JIT BPF code

On Wed, Jun 26, 2019 at 5:36 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> 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
> rename the variable to "jump_table" so objtool can recognize it.
>
> 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 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 080e2bb644cc..ff66294882f8 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] = {
>                 [0 ... 255] = &&default_label,
>                 /* Now overwrite non-defaults ... */
>                 BPF_INSN_MAP(BPF_INSN_2_LBL, BPF_INSN_3_LBL),
> @@ -1315,7 +1315,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
>  #define CONT_JMP ({ insn++; goto select_insn; })
>
>  select_insn:
> -       goto *jumptable[insn->code];
> +       goto *jump_table[insn->code];

I thought we were clear that it is a nack?
Either live it alone or rename to something like jump_table_bpf_interpreter
or bpf_interpreter_jump_table.