Re: [PATCH 1/2] tools/perf: Fix the string match for "/tmp/perf-$PID.map" files in dso__load

[Adrian Hunter]

On 14/06/24 20:27, 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 regex of form "/tmp/perf-*.map"
> 
> 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<atraj...@linux.vnet.ibm.com>
> ---
>  tools/perf/util/symbol.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 9e5940b5bc59..bfb88a4b0987 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -41,6 +41,7 @@
>  #include <limits.h>
>  #include <symbol/kallsyms.h>
>  #include <sys/utsname.h>
> +#include <regex.h>
>  
>  static int dso__load_kernel_sym(struct dso *dso, struct map *map);
>  static int dso__load_guest_kernel_sym(struct dso *dso, struct map *map);
> @@ -1797,9 +1798,18 @@ int dso__load(struct dso *dso, struct map *map)
>       struct nscookie nsc;
>       char newmapname[PATH_MAX];
>       const char *map_path = dso__long_name(dso);
> +     regex_t    regex;
> +     const char *pattern =  "(^/tmp/perf-).*(map)";
>  
>       mutex_lock(dso__lock(dso));
> -     perfmap = strncmp(dso__name(dso), "/tmp/perf-", 10) == 0;
> +     if (regcomp(&regex, pattern, REG_EXTENDED)) {
> +             pr_debug("regcomp() failed in dso__load\n");
> +             ret = -1;
> +             goto out;
> +     }
> +
> +     perfmap = !regexec(&regex, dso__name(dso), 0, NULL, 0);

This isn't the only place that checks for that name.  Perhaps
create a helper function:

bool is_perf_pid_map_name(const char *name);

Regex looks over complicated.  Maybe sscanf

        int tid;

        return sscanf(name, "/tmp/perf-%d.map", &tid) == 1;

> +
>       if (perfmap) {
>               if (dso__nsinfo(dso) &&
>                   (dso__find_perf_map(newmapname, sizeof(newmapname),