linux-kernel - Re: [PATCH 1/1 tip] perf: Don't assume /proc/kallsyms is ordered

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Date:	Tue, 26 May 2009 19:56:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, hpa@...or.com, paulus@...ba.org,
	linux-kernel@...r.kernel.org, jkacur@...hat.com, efault@....de,
	mtosatti@...hat.com, Thomas Gleixner <tglx@...utronix.de>,
	cjashfor@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/1 tip] perf: Don't assume /proc/kallsyms is ordered

On Tue, 2009-05-26 at 12:21 -0300, Arnaldo Carvalho de Melo wrote:
> Please fix the previous fix with this:

You don't need a second walk through the RB-tree like that, simply
change the lookup function:

The below finds the first entry that has ->start > ip, we then walk
backwards until we find an entry that has start <= ip < end and end > ip
(should never be more than 1).

This way you can deal with holes (like userspace has), and deal with
entries without size (like kallsyms) by setting size to a random large
value.

---

Index: linux-2.6/Documentation/perf_counter/builtin-report.c
===================================================================
--- linux-2.6.orig/Documentation/perf_counter/builtin-report.c
+++ linux-2.6/Documentation/perf_counter/builtin-report.c
@@ -147,16 +147,25 @@ static struct symbol *dso__find_symbol(s
 		return NULL;
 
 	struct rb_node *n = self->syms.rb_node;
+	struct rb_node *last = NULL;
+	struct symbol *s;
 
 	while (n) {
-		struct symbol *s = rb_entry(n, struct symbol, rb_node);
+		last = n;
+		s = rb_entry(n, struct symbol, rb_node);
 
 		if (ip < s->start)
 			n = n->rb_left;
-		else if (ip > s->end)
-			n = n->rb_right;
 		else
+			n = n->rb_right;
+	}
+
+	while (last) {
+		s = rb_entry(last, struct symbol, rb_node);
+		if (s->start <= ip && ip < s->end)
 			return s;
+
+		last = rb_prev(last);
 	}
 
 	return NULL;

--
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