perf tools: Add kallsyms__get_function_start()

Separate out the logic used to find the start address of the reference
symbol used to track kernel relocation.  kallsyms__get_function_start()
is used in subsequent patches.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Jiri Olsa <jolsa@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1391004884-10334-3-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 18 insertions, 3 deletions

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 1fc1c2f04772..17476df5c7b2 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -470,6 +470,17 @@ static int find_symbol_cb(void *arg, const char *name, char type,
         return 1;
 }
 
+u64 kallsyms__get_function_start(const char *kallsyms_filename,
+                                 const char *symbol_name)
+{
+        struct process_symbol_args args = { .name = symbol_name, };
+
+        if (kallsyms__parse(kallsyms_filename, &args, find_symbol_cb) <= 0)
+                return 0;
+
+        return args.start;
+}
+
 int perf_event__synthesize_kernel_mmap(struct perf_tool *tool,
                                        perf_event__handler_t process,
                                        struct machine *machine,
@@ -480,13 +491,13 @@ int perf_event__synthesize_kernel_mmap(struct perf_tool *tool,
         char path[PATH_MAX];
         char name_buff[PATH_MAX];
         struct map *map;
+        u64 start;
         int err;
         /*
          * We should get this from /sys/kernel/sections/.text, but till that is
          * available use this, and after it is use this as a fallback for older
          * kernels.
          */
-        struct process_symbol_args args = { .name = symbol_name, };
         union perf_event *event = zalloc((sizeof(event->mmap) +
                                           machine->id_hdr_size));
         if (event == NULL) {
@@ -513,7 +524,8 @@ int perf_event__synthesize_kernel_mmap(struct perf_tool *tool,
                 }
         }
 
-        if (kallsyms__parse(filename, &args, find_symbol_cb) <= 0) {
+        start = kallsyms__get_function_start(filename, symbol_name);
+        if (!start) {
                 free(event);
                 return -ENOENT;
         }
@@ -525,7 +537,7 @@ int perf_event__synthesize_kernel_mmap(struct perf_tool *tool,
         event->mmap.header.type = PERF_RECORD_MMAP;
         event->mmap.header.size = (sizeof(event->mmap) -
                         (sizeof(event->mmap.filename) - size) + machine->id_hdr_size);
-        event->mmap.pgoff = args.start;
+        event->mmap.pgoff = start;
         event->mmap.start = map->start;
         event->mmap.len   = map->end - event->mmap.start;
         event->mmap.pid   = machine->pid;
diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
index faf6e219be21..66a0c0392863 100644
--- a/tools/perf/util/event.h
+++ b/tools/perf/util/event.h
@@ -279,4 +279,7 @@ size_t perf_event__fprintf_mmap2(union perf_event *event, FILE *fp);
 size_t perf_event__fprintf_task(union perf_event *event, FILE *fp);
 size_t perf_event__fprintf(union perf_event *event, FILE *fp);
 
+u64 kallsyms__get_function_start(const char *kallsyms_filename,
+                                 const char *symbol_name);
+
 #endif /* __PERF_RECORD_H */