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>

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 8d08e75..4445a1e 100644 (file)
--- 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);

diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index bc06d3e..ed362ac 100644 (file)
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -86,6 +86,7 @@ struct line_range {
        int                     end;            /* End line number */
        int                     offset;         /* Start line offset */
        char                    *path;          /* Real path name */
+       char                    *comp_dir;      /* Compile directory */
        struct list_head        line_list;      /* Visible lines */
 };
 

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index a934a36..37dcdb6 100644 (file)
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -144,6 +144,15 @@ static const char *cu_find_realpath(Dwarf_Die *cu_die, const char *fname)
        return src;
 }
 
+/* Get DW_AT_comp_dir (should be NULL with older gcc) */
+static const char *cu_get_comp_dir(Dwarf_Die *cu_die)
+{
+       Dwarf_Attribute attr;
+       if (dwarf_attr(cu_die, DW_AT_comp_dir, &attr) == NULL)
+               return NULL;
+       return dwarf_formstring(&attr);
+}
+
 /* Compare diename and tname */
 static bool die_compare_name(Dwarf_Die *dw_die, const char *tname)
 {
@@ -1374,6 +1383,7 @@ int find_line_range(int fd, struct line_range *lr)
        size_t cuhl;
        Dwarf_Die *diep;
        Dwarf *dbg;
+       const char *comp_dir;
 
        dbg = dwarf_begin(fd, DWARF_C_READ);
        if (!dbg) {
@@ -1409,6 +1419,17 @@ int find_line_range(int fd, struct line_range *lr)
                }
                off = noff;
        }
+
+       /* Store comp_dir */
+       if (lf.found) {
+               comp_dir = cu_get_comp_dir(&lf.cu_die);
+               if (comp_dir) {
+                       lr->comp_dir = strdup(comp_dir);
+                       if (!lr->comp_dir)
+                               ret = -ENOMEM;
+               }
+       }
+
        pr_debug("path: %s\n", lr->path);
        dwarf_end(dbg);