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

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Date:   Wed, 26 Jun 2019 20:30:34 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.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 06:22:48PM -0700, Alexei Starovoitov wrote:
> On Wed, Jun 26, 2019 at 6:07 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >
> > On Wed, Jun 26, 2019 at 05:57:08PM -0700, Alexei Starovoitov wrote:
> > > 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.
> >
> > As I have said many times:
> >
> > The jump table detection is a generic objtool feature.  It makes no
> > sense to give a bpf-specific name to a generic objtool feature which can
> > be used by other components.
> 
> Nacked-by: Alexei Starovoitov <ast@...nel.org>

Whatever, it's your code...

To the -tip maintainers: patches 1 and 4 are independent of this change
and can be merged regardless.

-- 
Josh