linux-kernel - Re: [PATCH] perf symbols/KCORE: Rebuild rbtree when adjusting symbols for kcore

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Date:	Fri, 6 Nov 2015 15:59:29 +0200
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Wang Nan <wangnan0@...wei.com>
Cc:	namhyung@...nel.org, lizefan@...wei.com, pi3orama@....com,
	linux-kernel@...r.kernel.org, jolsa@...nel.org,
	masami.hiramatsu.pt@...achi.com
Subject: Re: [PATCH] perf symbols/KCORE: Rebuild rbtree when adjusting symbols
 for kcore

On 06/11/15 15:19, Arnaldo Carvalho de Melo wrote:
> Em Fri, Nov 06, 2015 at 09:46:12AM +0000, Wang Nan escreveu:
>> In dso__split_kallsyms_for_kcore(), current code adjusts symbol's
>> address but only reinsert it into rbtree if the symbol belongs to
>> another map. However, the expression for adjusting symbol (pos->start -=
>> curr_map->start - curr_map->pgoff) can change the relative order between
>> two symbols (even if the affected symbols are in different maps, in
>> kcore case they are possible to share one same dso), which damages the
>> rbtree.
> 
> Right, some code does change the symbol values it gets from whatever
> symtab (kallsyms, ELF, JIT maps, etc) when it should instead use the per
> map data structure (struct map) and its ->{map,unmap}_ip, ->pgoff,
> ->reloc, members for that :-\
> 
> I.e. 'struct dso' should be just what comes from the symtab, while
> 'struct map' should be about where that DSO is in memory.
> 
> With that in mind, do you still think your fix is the correct one?
> 
> Adrian?

The problem is when the order in memory (in kallsyms) is different
to the order on the dso (kcore).

I think to make it more general it needs to insert to a new tree.
e.g.


diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index b4cc7662677e..09343a880c0b 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -654,19 +654,24 @@ static int dso__split_kallsyms_for_kcore(struct dso *dso, struct map *map,
 	struct map_groups *kmaps = map__kmaps(map);
 	struct map *curr_map;
 	struct symbol *pos;
-	int count = 0, moved = 0;
+	int count = 0;
+	struct rb_root old_root = dso->symbols[map->type];
 	struct rb_root *root = &dso->symbols[map->type];
 	struct rb_node *next = rb_first(root);
 
 	if (!kmaps)
 		return -1;
 
+	*root = RB_ROOT;
+
 	while (next) {
 		char *module;
 
 		pos = rb_entry(next, struct symbol, rb_node);
 		next = rb_next(&pos->rb_node);
 
+		rb_erase_init(&pos->rb_node, &old_root);
+
 		module = strchr(pos->name, '\t');
 		if (module)
 			*module = '\0';
@@ -674,28 +679,21 @@ static int dso__split_kallsyms_for_kcore(struct dso *dso, struct map *map,
 		curr_map = map_groups__find(kmaps, map->type, pos->start);
 
 		if (!curr_map || (filter && filter(curr_map, pos))) {
-			rb_erase_init(&pos->rb_node, root);
 			symbol__delete(pos);
-		} else {
-			pos->start -= curr_map->start - curr_map->pgoff;
-			if (pos->end)
-				pos->end -= curr_map->start - curr_map->pgoff;
-			if (curr_map->dso != map->dso) {
-				rb_erase_init(&pos->rb_node, root);
-				symbols__insert(
-					&curr_map->dso->symbols[curr_map->type],
-					pos);
-				++moved;
-			} else {
-				++count;
-			}
+			continue;
 		}
+
+		pos->start -= curr_map->start - curr_map->pgoff;
+		if (pos->end)
+			pos->end -= curr_map->start - curr_map->pgoff;
+		symbols__insert(&curr_map->dso->symbols[curr_map->type], pos);
+		++count;
 	}
 
 	/* Symbols have been adjusted */
 	dso->adjust_symbols = 1;
 
-	return count + moved;
+	return count;
 }
 
 /*

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