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Message-ID: <20200428170143.zc2jvytxc5jqkxgb@treble>
Date: Tue, 28 Apr 2020 12:01:43 -0500
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Jann Horn <jannh@...gle.com>, Andy Lutomirski <luto@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
the arch/x86 maintainers <x86@...nel.org>,
kernel list <linux-kernel@...r.kernel.org>,
alexandre.chartre@...cle.com
Subject: Re: x86 entry perf unwinding failure (missing IRET_REGS annotation
on stack switch?)
On Tue, Apr 28, 2020 at 06:44:44PM +0200, Peter Zijlstra wrote:
> > > @@ -2494,8 +2494,16 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
> > > }
> > > }
> > >
> > > - if (skip_orig)
> > > + if (skip_orig) {
> > > + struct instruction *prev_insn = insn;
> > > + sec_for_each_insn_continue(file, insn) {
> > > + if (!insn->alt_group)
> > > + break;
> > > + if (!insn->visited)
> > > + insn->cfi = prev_insn->cfi;
> > > + }
> > > return 0;
> > > + }
> >
> > NACK :-)
> >
> > What happens if you have two alternatives adjacent to each other (which
> > can definitely happen in this scenario)?
>
> Alexandre's alt_group would help:
>
> 20200414103618.12657-3-alexandre.chartre@...cle.com
>
> Then we can do something like:
>
> static void fill_alternative(struct instruction *insn)
> {
> struct instruction *first_insn = insn;
> int alt_group = insn->alt_group;
>
> sec_for_each_insn_continue(file, insn) {
> if (insn->alt_group != alt_group)
> break;
> if (!insn->visited)
> insn->cfi = first_insn->cfi;
> }
> }
Ugh...
> > I still like my patch, at least the hack is done before the validate
> > code, so validate_branch() itself is simpler.
>
> But it doesn't handle the case where the alternatives themselves have
> unreachable holes in them, if that happens we'll generate spurious ORC
> entries for them.
Ah, I see what you mean.
I need to think about it...
--
Josh
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