linux-kernel - Re: [RFC PATCH 10/10] x86/unwind: add undwarf unwinder

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Message-ID: <20170601131020.fcyv77m3qb5v2zwc@hirez.programming.kicks-ass.net>
Date:   Thu, 1 Jun 2017 15:10:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>, Jiri Slaby <jslaby@...e.cz>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC PATCH 10/10] x86/unwind: add undwarf unwinder

On Thu, Jun 01, 2017 at 07:26:51AM -0500, Josh Poimboeuf wrote:
> On Thu, Jun 01, 2017 at 01:05:39PM +0200, Peter Zijlstra wrote:
> > On Thu, Jun 01, 2017 at 12:44:16AM -0500, Josh Poimboeuf wrote:
> > 
> > > +static struct undwarf *__undwarf_lookup(struct undwarf *undwarf,
> > > +					unsigned int num, unsigned long ip)
> > > +{
> > > +	struct undwarf *first = undwarf;
> > > +	struct undwarf *last = undwarf + num - 1;
> > > +	struct undwarf *mid;
> > > +	unsigned long u_ip;
> > > +
> > > +	while (first <= last) {
> > > +		mid = first + ((last - first) / 2);
> > > +		u_ip = undwarf_ip(mid);
> > > +
> > > +		if (ip >= u_ip) {
> > > +			if (ip < u_ip + mid->len)
> > > +				return mid;
> > > +			first = mid + 1;
> > > +		} else
> > > +			last = mid - 1;
> > > +	}
> > > +
> > > +	return NULL;
> > > +}
> > 
> > That's a bog standard binary search thing, don't we have a helper for
> > that someplace?
> 
> I wasn't able to find one...

Yeah, I looked too and couldn't find it either. A well.