perf symbols: Allow user probes on versioned symbols

Symbol versioning, as in glibc, results in symbols being defined as:

  <real symbol>@[@]<version>

(Note that "@@" identifies a default symbol, if the symbol name is
repeated.)

perf is currently unable to deal with this, and is unable to create user
probes at such symbols:

  --
  $ nm /lib/powerpc64le-linux-gnu/libpthread.so.0 | grep pthread_create
  0000000000008d30 t __pthread_create_2_1
  0000000000008d30 T pthread_create@@GLIBC_2.17
  $ /usr/bin/sudo perf probe -v -x /lib/powerpc64le-linux-gnu/libpthread.so.0 pthread_create
  probe-definition(0): pthread_create
  symbol:pthread_create file:(null) line:0 offset:0 return:0 lazy:(null)
  0 arguments
  Open Debuginfo file: /usr/lib/debug/lib/powerpc64le-linux-gnu/libpthread-2.19.so
  Try to find probe point from debuginfo.
  Probe point 'pthread_create' not found.
     Error: Failed to add events. Reason: No such file or directory (Code: -2)
  --

One is not able to specify the fully versioned symbol, either, due to
syntactic conflicts with other uses of "@" by perf:

  --
  $ /usr/bin/sudo perf probe -v -x /lib/powerpc64le-linux-gnu/libpthread.so.0 pthread_create@@GLIBC_2.17
  probe-definition(0): pthread_create@@GLIBC_2.17
  Semantic error :SRC@SRC is not allowed.
  0 arguments
     Error: Command Parse Error. Reason: Invalid argument (Code: -22)
  --

This patch ignores versioning for default symbols, thus allowing probes to be
created for these symbols:

  --
  $ /usr/bin/sudo ./perf probe -x /lib/powerpc64le-linux-gnu/libpthread.so.0 pthread_create
  Added new event:
     probe_libpthread:pthread_create (on pthread_create in /lib/powerpc64le-linux-gnu/libpthread-2.19.so)

  You can now use it in all perf tools, such as:

           perf record -e probe_libpthread:pthread_create -aR sleep 1

  $ /usr/bin/sudo ./perf record -e probe_libpthread:pthread_create -aR ./test 2
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.052 MB perf.data (2 samples) ]
  $ /usr/bin/sudo ./perf script
               test  2915 [000] 19124.260729: probe_libpthread:pthread_create: (3fff99248d38)
               test  2916 [000] 19124.260962: probe_libpthread:pthread_create: (3fff99248d38)
  $ /usr/bin/sudo ./perf probe --del=probe_libpthread:pthread_create
  Removed event: probe_libpthread:pthread_create
  --

Committer note:

Change the variable storing the result of strlen() to 'int', to fix the build
on debian:experimental-x-mipsel, fedora:24-x-ARC-uClibc, ubuntu:16.04-x-arm,
etc:

  util/symbol.c: In function 'symbol__match_symbol_name':
  util/symbol.c:422:11: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     if (len < versioning - name)
             ^

Signed-off-by: Paul A. Clarke <pc@us.ibm.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Link: http://lkml.kernel.org/r/c2b18d9c-17f8-9285-4868-f58b6359ccac@us.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 48 insertions, 13 deletions

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index b349e8eda0e2..8f2b068ff756 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -90,6 +90,17 @@ static int prefix_underscores_count(const char *str)
 	return tail - str;
 }
 
+int __weak arch__compare_symbol_names(const char *namea, const char *nameb)
+{
+	return strcmp(namea, nameb);
+}
+
+int __weak arch__compare_symbol_names_n(const char *namea, const char *nameb,
+					unsigned int n)
+{
+	return strncmp(namea, nameb, n);
+}
+
 int __weak arch__choose_best_symbol(struct symbol *syma,
 				    struct symbol *symb __maybe_unused)
 {
@@ -399,8 +410,26 @@ static void symbols__sort_by_name(struct rb_root *symbols,
 	}
 }
 
+int symbol__match_symbol_name(const char *name, const char *str,
+			      enum symbol_tag_include includes)
+{
+	const char *versioning;
+
+	if (includes == SYMBOL_TAG_INCLUDE__DEFAULT_ONLY &&
+	    (versioning = strstr(name, "@@"))) {
+		int len = strlen(str);
+
+		if (len < versioning - name)
+			len = versioning - name;
+
+		return arch__compare_symbol_names_n(name, str, len);
+	} else
+		return arch__compare_symbol_names(name, str);
+}
+
 static struct symbol *symbols__find_by_name(struct rb_root *symbols,
-					    const char *name)
+					    const char *name,
+					    enum symbol_tag_include includes)
 {
 	struct rb_node *n;
 	struct symbol_name_rb_node *s = NULL;
@@ -414,11 +443,11 @@ static struct symbol *symbols__find_by_name(struct rb_root *symbols,
 		int cmp;
 
 		s = rb_entry(n, struct symbol_name_rb_node, rb_node);
-		cmp = arch__compare_symbol_names(name, s->sym.name);
+		cmp = symbol__match_symbol_name(s->sym.name, name, includes);
 
-		if (cmp < 0)
+		if (cmp > 0)
 			n = n->rb_left;
-		else if (cmp > 0)
+		else if (cmp < 0)
 			n = n->rb_right;
 		else
 			break;
@@ -427,16 +456,17 @@ static struct symbol *symbols__find_by_name(struct rb_root *symbols,
 	if (n == NULL)
 		return NULL;
 
-	/* return first symbol that has same name (if any) */
-	for (n = rb_prev(n); n; n = rb_prev(n)) {
-		struct symbol_name_rb_node *tmp;
+	if (includes != SYMBOL_TAG_INCLUDE__DEFAULT_ONLY)
+		/* return first symbol that has same name (if any) */
+		for (n = rb_prev(n); n; n = rb_prev(n)) {
+			struct symbol_name_rb_node *tmp;
 
-		tmp = rb_entry(n, struct symbol_name_rb_node, rb_node);
-		if (arch__compare_symbol_names(tmp->sym.name, s->sym.name))
-			break;
+			tmp = rb_entry(n, struct symbol_name_rb_node, rb_node);
+			if (arch__compare_symbol_names(tmp->sym.name, s->sym.name))
+				break;
 
-		s = tmp;
-	}
+			s = tmp;
+		}
 
 	return &s->sym;
 }
@@ -503,7 +533,12 @@ struct symbol *symbol__next_by_name(struct symbol *sym)
 struct symbol *dso__find_symbol_by_name(struct dso *dso, enum map_type type,
 					const char *name)
 {
-	return symbols__find_by_name(&dso->symbol_names[type], name);
+	struct symbol *s = symbols__find_by_name(&dso->symbol_names[type], name,
+						 SYMBOL_TAG_INCLUDE__NONE);
+	if (!s)
+		s = symbols__find_by_name(&dso->symbol_names[type], name,
+					  SYMBOL_TAG_INCLUDE__DEFAULT_ONLY);
+	return s;
 }
 
 void dso__sort_by_name(struct dso *dso, enum map_type type)