perf symbols: Use the buildids if present

With this change 'perf record' will intercept PERF_RECORD_MMAP
calls, creating a linked list of DSOs, then when the session
finishes, it will traverse this list and read the buildids,
stashing them at the end of the file and will set up a new
feature bit in the header bitmask.

'perf report' will then notice this feature and populate the
'dsos' list and set the build ids.

When reading the symtabs it will refuse to load from a file that
doesn't have the same build id. This improves the
reliability of the profiler output, as symbols and profiling
data is more guaranteed to match.

Example:

 [root@doppio ~]# perf report | head
 /home/acme/bin/perf with build id b1ea544ac3746e7538972548a09aadecc5753868 not found, continuing without symbols
  # Samples: 2621434559
  #
  # Overhead          Command                  Shared Object  Symbol
  # ........  ...............  .............................  ......
  #
       7.91%             init  [kernel]        [k] read_hpet
       7.64%             init  [kernel]        [k] mwait_idle_with_hints
       7.60%          swapper  [kernel]        [k] read_hpet
       7.60%          swapper  [kernel]        [k] mwait_idle_with_hints
       3.65%             init  [kernel]        [k] 0xffffffffa02339d9
[root@doppio ~]#

In this case the 'perf' binary was an older one, vanished,
so its symbols probably wouldn't match or would cause subtly
different (and misleading) output.

Next patches will support the kernel as well, reading the build
id notes for it and the modules from /sys.

Another patch should also introduce a new plumbing command:

'perf list-buildids'

that will then be used in porcelain that is distro specific to
fetch -debuginfo packages where such buildids are present. This
will in turn allow for one to run 'perf record' in one machine
and 'perf report' in another.

Future work on having the buildid sent directly from the kernel
in the PERF_RECORD_MMAP event is needed to close races, as the
DSO can be changed during a 'perf record' session, but this
patch at least helps with non-corner cases and current/older
kernels.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Frank Ch. Eigler <fche@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: K. Prasad <prasad@linux.vnet.ibm.com>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roland McGrath <roland@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1257367843-26224-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 46 insertions, 3 deletions

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 4a73d89ce5d..ab333812ace 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -17,6 +17,7 @@
 #include "util/header.h"
 #include "util/event.h"
 #include "util/debug.h"
+#include "util/symbol.h"
 
 #include <unistd.h>
 #include <sched.h>
@@ -109,9 +110,21 @@ static void write_output(void *buf, size_t size)
         }
 }
 
+static void write_event(event_t *buf, size_t size)
+{
+        /*
+        * Add it to the list of DSOs, so that when we finish this
+         * record session we can pick the available build-ids.
+         */
+        if (buf->header.type == PERF_RECORD_MMAP)
+                dsos__findnew(buf->mmap.filename);
+
+        write_output(buf, size);
+}
+
 static int process_synthesized_event(event_t *event)
 {
-        write_output(event, event->header.size);
+        write_event(event, event->header.size);
         return 0;
 }
 
@@ -163,14 +176,14 @@ static void mmap_read(struct mmap_data *md)
                 size = md->mask + 1 - (old & md->mask);
                 old += size;
 
-                write_output(buf, size);
+                write_event(buf, size);
         }
 
         buf = &data[old & md->mask];
         size = head - old;
         old += size;
 
-        write_output(buf, size);
+        write_event(buf, size);
 
         md->prev = old;
         mmap_write_tail(md, old);
@@ -365,10 +378,38 @@ static void open_counters(int cpu, pid_t pid)
         nr_cpu++;
 }
 
+static bool write_buildid_table(void)
+{
+        struct dso *pos;
+        bool have_buildid = false;
+
+        list_for_each_entry(pos, &dsos, node) {
+                struct build_id_event b;
+                size_t len;
+
+                if (filename__read_build_id(pos->long_name,
+                                            &b.build_id,
+                                            sizeof(b.build_id)) < 0)
+                        continue;
+                have_buildid = true;
+                memset(&b.header, 0, sizeof(b.header));
+                len = strlen(pos->long_name) + 1;
+                len = ALIGN(len, 64);
+                b.header.size = sizeof(b) + len;
+                write_output(&b, sizeof(b));
+                write_output(pos->long_name, len);
+        }
+
+        return have_buildid;
+}
+
 static void atexit_header(void)
 {
         header->data_size += bytes_written;
 
+        if (write_buildid_table())
+                perf_header__set_feat(header, HEADER_BUILD_ID);
+
         perf_header__write(header, output);
 }
 
@@ -572,6 +613,8 @@ int cmd_record(int argc, const char **argv, const char *prefix __used)
 {
         int counter;
 
+        symbol__init(0);
+
         argc = parse_options(argc, argv, options, record_usage,
                 PARSE_OPT_STOP_AT_NON_OPTION);
         if (!argc && target_pid == -1 && !system_wide)