[PATCH V3 1/3] tools/perf: Fix the string match for "/tmp/perf-$PID.map" files in dso__load

Athira Rajeev
2024-06-18T14:04:26Z

Perf test for perf probe of function from different CU fails
as below:

./perf test -vv "test perf probe of function from different CU"
116: test perf probe of function from different CU:
--- start ---
test child forked, pid 2679
Failed to find symbol foo in /tmp/perf-uprobe-different-cu-sh.Msa7iy89bx/testfile
Error: Failed to add events.
--- Cleaning up ---
"foo" does not hit any event.
Error: Failed to delete events.
---- end(-1) ----
116: test perf probe of function from different CU : FAILED!

The test does below to probe function "foo" :

# gcc -g -Og -flto -c /tmp/perf-uprobe-different-cu-sh.XniNxNEVT7/testfile-foo.c
-o /tmp/perf-uprobe-different-cu-sh.XniNxNEVT7/testfile-foo.o
# gcc -g -Og -c /tmp/perf-uprobe-different-cu-sh.XniNxNEVT7/testfile-main.c
-o /tmp/perf-uprobe-different-cu-sh.XniNxNEVT7/testfile-main.o
# gcc -g -Og -o /tmp/perf-uprobe-different-cu-sh.XniNxNEVT7/testfile
/tmp/perf-uprobe-different-cu-sh.XniNxNEVT7/testfile-foo.o
/tmp/perf-uprobe-different-cu-sh.XniNxNEVT7/testfile-main.o

# ./perf probe -x /tmp/perf-uprobe-different-cu-sh.XniNxNEVT7/testfile foo
Failed to find symbol foo in /tmp/perf-uprobe-different-cu-sh.XniNxNEVT7/testfile
Error: Failed to add events.

Perf probe fails to find symbol foo in the executable placed in
/tmp/perf-uprobe-different-cu-sh.XniNxNEVT7

Simple reproduce:

# mktemp -d /tmp/perf-checkXXXXXXXXXX
/tmp/perf-checkcWpuLRQI8j

# gcc -g -o test test.c
# cp test /tmp/perf-checkcWpuLRQI8j/
# nm /tmp/perf-checkcWpuLRQI8j/test | grep foo
00000000100006bc T foo

# ./perf probe -x /tmp/perf-checkcWpuLRQI8j/test foo
Failed to find symbol foo in /tmp/perf-checkcWpuLRQI8j/test
Error: Failed to add events.

But it works with any files like /tmp/perf/test. Only for
patterns with "/tmp/perf-", this fails.

Further debugging, commit 80d496be89ed ("perf report: Add support
for profiling JIT generated code") added support for profiling JIT
generated code. This patch handles dso's of form
"/tmp/perf-$PID.map" .

The check used "if (strncmp(self->name, "/tmp/perf-", 10) == 0)"
to match "/tmp/perf-$PID.map". With this commit, any dso in
/tmp/perf- folder will be considered separately for processing
(not only JIT created map files ). Fix this by changing the
string pattern to check for "/tmp/perf-%d.map". Add a helper
function is_perf_pid_map_name to do this check.

With the fix,
# ./perf test "test perf probe of function from different CU"
117: test perf probe of function from different CU : Ok

Signed-off-by: Athira Rajeev<atrajeev@linux.vnet.ibm.com>
---
Changelog:
v2 -> v3:
Addressed review comment from Adrian and James.
Added perf_pid_map_tid to save the tid and modified
is_perf_pid_map_name to use this internally.

v1 -> v2:
Addressed review comments from Adrian.
Added helper function is_perf_pid_map_name to check
dso name of form "/tmp/perf-%d.map". Used sscanf
instead of regex comparison.

tools/perf/util/dso.c | 12 ++++++++++++
tools/perf/util/dso.h | 4 ++++
tools/perf/util/symbol.c | 3 ++-
3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index dde706b71da7..2340c4f6d0c2 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -1652,3 +1652,15 @@ int dso__strerror_load(struct dso *dso, char *buf, size_t buflen)
scnprintf(buf, buflen, "%s", dso_load__error_str[idx]);
return 0;
}
+
+bool perf_pid_map_tid(const char *dso_name, int *tid)
+{
+ return sscanf(dso_name, "/tmp/perf-%d.map", tid) == 1;
+}
+
+bool is_perf_pid_map_name(const char *dso_name)
+{
+ int tid;
+
+ return perf_pid_map_tid(dso_name, &tid);
+}
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index df2c98402af3..d72f3b8c37f6 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -809,4 +809,8 @@ void reset_fd_limit(void);
u64 dso__find_global_type(struct dso *dso, u64 addr);
u64 dso__findnew_global_type(struct dso *dso, u64 addr, u64 offset);

+/* Check if dso name is of format "/tmp/perf-%d.map" */
+bool perf_pid_map_tid(const char *dso_name, int *tid);
+bool is_perf_pid_map_name(const char *dso_name);
+
#endif /* __PERF_DSO */
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 9e5940b5bc59..aee0a4cfb383 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1799,7 +1799,8 @@ int dso__load(struct dso *dso, struct map *map)
const char *map_path = dso__long_name(dso);

mutex_lock(dso__lock(dso));
- perfmap = strncmp(dso__name(dso), "/tmp/perf-", 10) == 0;
+ perfmap = is_perf_pid_map_name(map_path);
+
if (perfmap) {
if (dso__nsinfo(dso) &&
(dso__find_perf_map(newmapname, sizeof(newmapname),
--
2.35.3