perf symbols: Add some heuristics for choosing the best duplicate symbol

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>

1 files changed, 88 insertions, 0 deletions

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 0d94ddb55bd7..870b3b8c649b 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) {
                         /*