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Date: Fri, 24 Jul 2015 12:56:02 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Jason Baron <jasonbaron0@...il.com> Cc: Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...capital.net>, Thomas Gleixner <tglx@...utronix.de>, Mikulas Patocka <mpatocka@...hat.com>, Paul Mackerras <paulus@...ba.org>, Arnaldo Carvalho de Melo <acme@...nel.org>, Kees Cook <keescook@...omium.org>, Andrea Arcangeli <aarcange@...hat.com>, Vince Weaver <vince@...ter.net>, "hillf.zj" <hillf.zj@...baba-inc.com>, Valdis Kletnieks <Valdis.Kletnieks@...edu>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Steven Rostedt <rostedt@...dmis.org> Subject: Re: Kernel broken on processors without performance counters On Thu, Jul 23, 2015 at 03:14:13PM -0400, Jason Baron wrote: > > +static enum jump_label_type jump_label_type(struct jump_entry *entry) > > +{ > > + struct static_key *key = static_key_cast(iter->key); > > + bool true_branch = jump_label_get_branch_default(key); > > + bool state = static_key_enabled(key); > > + bool inv = static_key_inv(iter->key); > > + > > + return (true_branch ^ state) ^ inv; > > iiuc...this allows both the old style keys to co-exist with the > new ones. IE state wouldn't be set for the new ones. And inv > shouldn't be set for the old ones. Is that correct? @state is the dynamic variable here, the other two are compile time. @true_branch denotes the default (compile time) value, and @inv denotes the (compile time) branch preference. So @state will still be set for the new ones, but you're right in that @inv will not be set for the 'legacy' stuff. This one little line needs a big comment. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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