perf symbols: Save DSO loading errno to better report errors

Before, when some problem happened while trying to load the kernel
symtab, 'perf top' would show:

      ┌─Warning:───────────────────────────┐
      │The vmlinux file can't be used.     │
      │Kernel samples will not be resolved.│
      │                                    │
      │                                    │
      │Press any key...                    │
      └────────────────────────────────────┘

Now, it reports:

  # perf top --vmlinux /dev/null

      ┌─Warning:───────────────────────────────────────────┐
      │The /tmp/passwd file can't be used: Invalid ELF file│
      │Kernel samples will not be resolved.                │
      │                                                    │
      │                                                    │
      │Press any key...                                    │
      └────────────────────────────────────────────────────┘

This is possible because we now register the reason for not being able
to load the symtab in the dso->load_errno member, and provide a
dso__strerror_load() routine to format this error into a strerror like
string with a short reason for the error while loading.

That can be just forwarding the dso__strerror_load() call to
strerror_r(), or, for a separate errno range providing a custom message.

Reported-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-u5rb5uq63xqhkfb8uv2lxd5u@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 5fb8723c7128..1cb3436276d1 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -757,8 +757,10 @@ static void perf_event__process_sample(struct perf_tool *tool,
 		    al.map == machine->vmlinux_maps[MAP__FUNCTION] &&
 		    RB_EMPTY_ROOT(&al.map->dso->symbols[MAP__FUNCTION])) {
 			if (symbol_conf.vmlinux_name) {
-				ui__warning("The %s file can't be used.\n%s",
-					    symbol_conf.vmlinux_name, msg);
+				char serr[256];
+				dso__strerror_load(al.map->dso, serr, sizeof(serr));
+				ui__warning("The %s file can't be used: %s\n%s",
+					    symbol_conf.vmlinux_name, serr, msg);
 			} else {
 				ui__warning("A vmlinux file was not found.\n%s",
 					    msg);