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Date: Tue, 28 Apr 2020 18:44:44 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Josh Poimboeuf <jpoimboe@...hat.com> 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 10:49:09AM -0500, Josh Poimboeuf wrote: > > @@ -2439,12 +2445,6 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, > > > > sec = insn->sec; > > > > - if (insn->alt_group && list_empty(&insn->alts)) { > > - WARN_FUNC("don't know how to handle branch to middle of alternative instruction group", > > - sec, insn->offset); > > - return 1; > > - } > > - > > ACK (separate patch) > > > while (1) { > > next_insn = next_insn_same_sec(file, insn); > > Yeah, there is one from Julien that does this: 20200327152847.15294-6-jthierry@...hat.com > > @@ -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; } } > 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.
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