perf probe: Support comp_dir to find an absolute source path

Gcc generates DW_AT_comp_dir and stores relative source path if building kernel
without O= option. In that case, perf probe --line sometimes doesn't work
without --source option, because it tries to access relative source path.

This adds DW_AT_comp_dir support to perf probe for finding an absolute source
path when no --source option.

LKML-Reference: <4C36EBE7.3060802@hitachi.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 22 insertions, 12 deletions

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 8d08e75b2dd3..4445a1e7052f 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -201,28 +201,38 @@ static int try_to_find_kprobe_trace_events(struct perf_probe_event *pev,
  * a newly allocated path on success.
  * Return 0 if file was found and readable, -errno otherwise.
  */
-static int get_real_path(const char *raw_path, char **new_path)
+static int get_real_path(const char *raw_path, const char *comp_dir,
+                         char **new_path)
 {
-        if (!symbol_conf.source_prefix) {
-                if (access(raw_path, R_OK) == 0) {
-                        *new_path = strdup(raw_path);
-                        return 0;
-                } else
-                        return -errno;
+        const char *prefix = symbol_conf.source_prefix;
+
+        if (!prefix) {
+                if (raw_path[0] != '/' && comp_dir)
+                        /* If not an absolute path, try to use comp_dir */
+                        prefix = comp_dir;
+                else {
+                        if (access(raw_path, R_OK) == 0) {
+                                *new_path = strdup(raw_path);
+                                return 0;
+                        } else
+                                return -errno;
+                }
         }
 
-        *new_path = malloc((strlen(symbol_conf.source_prefix) +
-                            strlen(raw_path) + 2));
+        *new_path = malloc((strlen(prefix) + strlen(raw_path) + 2));
         if (!*new_path)
                 return -ENOMEM;
 
         for (;;) {
-                sprintf(*new_path, "%s/%s", symbol_conf.source_prefix,
-                        raw_path);
+                sprintf(*new_path, "%s/%s", prefix, raw_path);
 
                 if (access(*new_path, R_OK) == 0)
                         return 0;
 
+                if (!symbol_conf.source_prefix)
+                        /* In case of searching comp_dir, don't retry */
+                        return -errno;
+
                 switch (errno) {
                 case ENAMETOOLONG:
                 case ENOENT:
@@ -318,7 +328,7 @@ int show_line_range(struct line_range *lr)
 
         /* Convert source file path */
         tmp = lr->path;
-        ret = get_real_path(tmp, &lr->path);
+        ret = get_real_path(tmp, lr->comp_dir, &lr->path);
         free(tmp);      /* Free old path */
         if (ret < 0) {
                 pr_warning("Failed to find source file. (%d)\n", ret);