[PATCH 05/12] perf symbols: Add some heuristics for choosing the best duplicate symbol

Arnaldo Carvalho de Melo
2011-09-23T20:26:37Z

From: Anton Blanchard <anton@samba.org>

Try and pick the best symbol based on a few heuristics:

- Prefer a non weak symbol over a weak one
- Prefer a global symbol over a non global one
- Prefer a symbol with less underscores (idea taken from kallsyms.c)
- If all else fails, choose the symbol with the longest name

Cc: Eric B Munson <emunson@mgebm.net>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110824065243.161953371@samba.org
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/symbol.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 88 insertions(+), 0 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 0d94ddb..870b3b8 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -86,6 +86,92 @@ bool symbol_type__is_a(char symbol_type, enum map_type map_type)
}
}

+static int prefix_underscores_count(const char *str)
+{
+ const char *tail = str;
+
+ while (*tail == '_')
+ tail++;
+
+ return tail - str;
+}
+
+#define SYMBOL_A 0
+#define SYMBOL_B 1
+
+static int choose_best_symbol(struct symbol *syma, struct symbol *symb)
+{
+ s64 a;
+ s64 b;
+
+ /* Prefer a symbol with non zero length */
+ a = syma->end - syma->start;
+ b = symb->end - symb->start;
+ if ((b == 0) && (a > 0))
+ return SYMBOL_A;
+ else if ((a == 0) && (b > 0))
+ return SYMBOL_B;
+
+ /* Prefer a non weak symbol over a weak one */
+ a = syma->binding == STB_WEAK;
+ b = symb->binding == STB_WEAK;
+ if (b && !a)
+ return SYMBOL_A;
+ if (a && !b)
+ return SYMBOL_B;
+
+ /* Prefer a global symbol over a non global one */
+ a = syma->binding == STB_GLOBAL;
+ b = symb->binding == STB_GLOBAL;
+ if (a && !b)
+ return SYMBOL_A;
+ if (b && !a)
+ return SYMBOL_B;
+
+ /* Prefer a symbol with less underscores */
+ a = prefix_underscores_count(syma->name);
+ b = prefix_underscores_count(symb->name);
+ if (b > a)
+ return SYMBOL_A;
+ else if (a > b)
+ return SYMBOL_B;
+
+ /* If all else fails, choose the symbol with the longest name */
+ if (strlen(syma->name) >= strlen(symb->name))
+ return SYMBOL_A;
+ else
+ return SYMBOL_B;
+}
+
+static void symbols__fixup_duplicate(struct rb_root *symbols)
+{
+ struct rb_node *nd;
+ struct symbol *curr, *next;
+
+ nd = rb_first(symbols);
+
+ while (nd) {
+ curr = rb_entry(nd, struct symbol, rb_node);
+again:
+ nd = rb_next(&curr->rb_node);
+ next = rb_entry(nd, struct symbol, rb_node);
+
+ if (!nd)
+ break;
+
+ if (curr->start != next->start)
+ continue;
+
+ if (choose_best_symbol(curr, next) == SYMBOL_A) {
+ rb_erase(&next->rb_node, symbols);
+ goto again;
+ } else {
+ nd = rb_next(&curr->rb_node);
+ rb_erase(&curr->rb_node, symbols);
+ }
+ }
+}
+
static void symbols__fixup_end(struct rb_root *symbols)
{
struct rb_node *nd, *prevnd = rb_first(symbols);
@@ -692,6 +778,7 @@ int dso__load_kallsyms(struct dso *dso, const char *filename,
if (dso__load_all_kallsyms(dso, filename, map) < 0)
return -1;

+ symbols__fixup_duplicate(&dso->symbols[map->type]);
symbols__fixup_end(&dso->symbols[map->type]);

if (dso->kernel == DSO_TYPE_GUEST_KERNEL)
@@ -1269,6 +1356,7 @@ new_symbol:
* For misannotated, zeroed, ASM function sizes.
*/
if (nr > 0) {
+ symbols__fixup_duplicate(&dso->symbols[map->type]);
symbols__fixup_end(&dso->symbols[map->type]);
if (kmap) {
/*
--
1.6.2.5