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Subject[PATCH v3] Allow user probes on versioned symbols
Date
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)
--

The attached 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
--

Signed-off-by: Paul A. Clarke <pc@us.ibm.com>
---
v3:
- code style fixes per David Ahern

v2:
- move logic from arch__compare_symbol_names to new map__compare_symbol_names
- call through from map__compare_symbol_names to arch__compare_symbol_names
- redirect uses of arch__compare_symbol_names
- send patch to LKML

tools/perf/util/auxtrace.c | 2 +-
tools/perf/util/map.c | 23 +++++++++++++++++++++++
tools/perf/util/map.h | 3 ++-
tools/perf/util/symbol.c | 4 ++--
4 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
index c5a6e0b1..f3511a6 100644
--- a/tools/perf/util/auxtrace.c
+++ b/tools/perf/util/auxtrace.c
@@ -1875,7 +1875,7 @@ static bool dso_sym_match(struct symbol *sym, const char *name, int *cnt,
int idx)
{
/* Same name, and global or the n'th found or any */
- return !arch__compare_symbol_names(name, sym->name) &&
+ return !map__compare_symbol_names(name, sym->name) &&
((!idx && sym->binding == STB_GLOBAL) ||
(idx > 0 && ++*cnt == idx) ||
idx < 0);
diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
index 4f9a71c..26a3e87 100644
--- a/tools/perf/util/map.c
+++ b/tools/perf/util/map.c
@@ -330,6 +330,29 @@ int __weak arch__compare_symbol_names(const char *namea, const char *nameb)
return strcmp(namea, nameb);
}

+int map__compare_symbol_names(const char *namea, const char *nameb)
+{
+ int rc;
+ const char *namea_versioning, *nameb_versioning;
+
+ namea_versioning = strstr(namea,"@@");
+ if (namea_versioning)
+ namea = strndup(namea,namea_versioning-namea);
+
+ nameb_versioning = strstr(nameb,"@@");
+ if (nameb_versioning)
+ nameb = strndup(nameb,nameb_versioning-nameb);
+
+ rc = arch__compare_symbol_names(namea, nameb);
+
+ if (namea_versioning)
+ free((void *)namea);
+ if (nameb_versioning)
+ free((void *)nameb);
+
+ return rc;
+}
+
struct symbol *map__find_symbol(struct map *map, u64 addr)
{
if (map__load(map) < 0)
diff --git a/tools/perf/util/map.h b/tools/perf/util/map.h
index abdacf8..aaad64d 100644
--- a/tools/perf/util/map.h
+++ b/tools/perf/util/map.h
@@ -130,13 +130,14 @@ struct thread;
*/
#define __map__for_each_symbol_by_name(map, sym_name, pos) \
for (pos = map__find_symbol_by_name(map, sym_name); \
- pos && arch__compare_symbol_names(pos->name, sym_name) == 0; \
+ pos && map__compare_symbol_names(pos->name, sym_name) == 0; \
pos = symbol__next_by_name(pos))

#define map__for_each_symbol_by_name(map, sym_name, pos) \
__map__for_each_symbol_by_name(map, sym_name, (pos))

int arch__compare_symbol_names(const char *namea, const char *nameb);
+int map__compare_symbol_names(const char *namea, const char *nameb);
void map__init(struct map *map, enum map_type type,
u64 start, u64 end, u64 pgoff, struct dso *dso);
struct map *map__new(struct machine *machine, u64 start, u64 len,
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index dc93940..4fb9d275 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -411,7 +411,7 @@ 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 = map__compare_symbol_names(name, s->sym.name);

if (cmp < 0)
n = n->rb_left;
@@ -429,7 +429,7 @@ static struct symbol *symbols__find_by_name(struct rb_root *symbols,
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))
+ if (map__compare_symbol_names(tmp->sym.name, s->sym.name))
break;

s = tmp;
--
2.1.4
Regards,
PC

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