Re: [PATCH V4 1/3] tools/perf: Fix the string match for "/tmp/perf-$PID.map" files in dso__load

Adrian Hunter
2024-06-25T11:57:35Z

On 23/06/24 09:48, Athira Rajeev wrote:
> 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. In "struct dso",
> dso->long_name holds the long name of the dso file. Since the
> /tmp/perf-$PID.map check uses the complete name, use dso___long_name for
> the string name.
>
> 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>

Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>

> ---
> Changelog:
> v3 -> v4:
> Added commit message with usage of dso__long_name
>
> 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),