perf symbols: Add symfs option for off-box analysis using specified tree

The symfs argument allows analysis of perf.data file using a locally accessible
filesystem tree with debug symbols - e.g., tree created during image builds,
sshfs mount, loop mounted KVM disk images, USB keys, initrds, etc. Anything
with an OS tree can be analyzed from anywhere without the need to populate a
local data store with build-ids.

Commiter notes:

o Fixed up symfs="/" variants handling.

o prefixed DSO__ORIG_GUEST_KMODULE case with symfs too, avoiding use of files
  outside the symfs directory.

LKML-Reference: <1291926427-28846-1-git-send-email-daahern@cisco.com>
Signed-off-by: David Ahern <daahern@cisco.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index a3b84160c42e..d5036700a435 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -1092,6 +1092,12 @@ int hist_entry__annotate(struct hist_entry *self, struct list_head *head,
         FILE *file;
         int err = 0;
         u64 len;
+        char symfs_filename[PATH_MAX];
+
+        if (filename) {
+                snprintf(symfs_filename, sizeof(symfs_filename), "%s%s",
+                         symbol_conf.symfs, filename);
+        }
 
         if (filename == NULL) {
                 if (dso->has_build_id) {
@@ -1100,9 +1106,9 @@ int hist_entry__annotate(struct hist_entry *self, struct list_head *head,
                         return -ENOMEM;
                 }
                 goto fallback;
-        } else if (readlink(filename, command, sizeof(command)) < 0 ||
+        } else if (readlink(symfs_filename, command, sizeof(command)) < 0 ||
                    strstr(command, "[kernel.kallsyms]") ||
-                   access(filename, R_OK)) {
+                   access(symfs_filename, R_OK)) {
                 free(filename);
 fallback:
                 /*
@@ -1111,6 +1117,8 @@ fallback:
                  * DSO is the same as when 'perf record' ran.
                  */
                 filename = dso->long_name;
+                snprintf(symfs_filename, sizeof(symfs_filename), "%s%s",
+                         symbol_conf.symfs, filename);
                 free_filename = false;
         }
 
@@ -1137,7 +1145,7 @@ fallback:
                  "objdump --start-address=0x%016Lx --stop-address=0x%016Lx -dS -C %s|grep -v %s|expand",
                  map__rip_2objdump(map, sym->start),
                  map__rip_2objdump(map, sym->end),
-                 filename, filename);
+                 symfs_filename, filename);
 
         pr_debug("Executing: %s\n", command);