perf tools: Back [vdso] DSO with real data

Storing data for VDSO shared object, because we need it for the post
unwind processing.

The VDSO shared object is same for all process on a running system, so
it makes no difference when we store it inside the tracer - perf.

When [vdso] map memory is hit, we retrieve [vdso] DSO image and store it
into temporary file.

During the build-id processing phase, the [vdso] DSO image is stored in
build-id db, and build-id reference is made inside perf.data. The
build-id vdso file object is called '[vdso]'. We don't use temporary
file name which gets removed when record is finished.

During report phase the vdso build-id object is treated as any other
build-id DSO object.

Adding following API for vdso object:

  bool is_vdso_map(const char *filename)
    - returns true if the filename matches vdso map name

  struct dso *vdso__dso_findnew(struct list_head *head)
    - find/create proper vdso DSO object

  vdso__exit(void)
    - removes temporary VDSO image if there's any

This change makes backtrace dwarf post unwind possible from [vdso] maps.

Following output is current report of [vdso] sample dwarf backtrace:

  # Overhead  Command      Shared Object                         Symbol
  # ........  .......  .................  .............................
  #
      99.52%       ex  [vdso]             [.] 0x00007fff3ace89af
                   |
                   --- 0x7fff3ace89af

Following output is new report of [vdso] sample dwarf backtrace:

  # Overhead  Command      Shared Object                         Symbol
  # ........  .......  .................  .............................
  #
      99.52%       ex  [vdso]             [.] 0x00000000000009af
                   |
                   --- 0x7fff3ace89af
                       main
                       __libc_start_main
                       _start

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1347295819-23177-5-git-send-email-jolsa@redhat.com
[ committer note: s/ALIGN/PERF_ALIGN/g to cope with the android build changes ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 111 insertions, 0 deletions

diff --git a/tools/perf/util/vdso.c b/tools/perf/util/vdso.c
new file mode 100644
index 000000000000..e60951fcdb12
--- /dev/null
+++ b/tools/perf/util/vdso.c
@@ -0,0 +1,111 @@
+
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <linux/kernel.h>
+
+#include "vdso.h"
+#include "util.h"
+#include "symbol.h"
+#include "linux/string.h"
+
+static bool vdso_found;
+static char vdso_file[] = "/tmp/perf-vdso.so-XXXXXX";
+
+static int find_vdso_map(void **start, void **end)
+{
+        FILE *maps;
+        char line[128];
+        int found = 0;
+
+        maps = fopen("/proc/self/maps", "r");
+        if (!maps) {
+                pr_err("vdso: cannot open maps\n");
+                return -1;
+        }
+
+        while (!found && fgets(line, sizeof(line), maps)) {
+                int m = -1;
+
+                /* We care only about private r-x mappings. */
+                if (2 != sscanf(line, "%p-%p r-xp %*x %*x:%*x %*u %n",
+                                start, end, &m))
+                        continue;
+                if (m < 0)
+                        continue;
+
+                if (!strncmp(&line[m], VDSO__MAP_NAME,
+                             sizeof(VDSO__MAP_NAME) - 1))
+                        found = 1;
+        }
+
+        fclose(maps);
+        return !found;
+}
+
+static char *get_file(void)
+{
+        char *vdso = NULL;
+        char *buf = NULL;
+        void *start, *end;
+        size_t size;
+        int fd;
+
+        if (vdso_found)
+                return vdso_file;
+
+        if (find_vdso_map(&start, &end))
+                return NULL;
+
+        size = end - start;
+
+        buf = memdup(start, size);
+        if (!buf)
+                return NULL;
+
+        fd = mkstemp(vdso_file);
+        if (fd < 0)
+                goto out;
+
+        if (size == (size_t) write(fd, buf, size))
+                vdso = vdso_file;
+
+        close(fd);
+
+ out:
+        free(buf);
+
+        vdso_found = (vdso != NULL);
+        return vdso;
+}
+
+void vdso__exit(void)
+{
+        if (vdso_found)
+                unlink(vdso_file);
+}
+
+struct dso *vdso__dso_findnew(struct list_head *head)
+{
+        struct dso *dso = dsos__find(head, VDSO__MAP_NAME);
+
+        if (!dso) {
+                char *file;
+
+                file = get_file();
+                if (!file)
+                        return NULL;
+
+                dso = dso__new(VDSO__MAP_NAME);
+                if (dso != NULL) {
+                        dsos__add(head, dso);
+                        dso__set_long_name(dso, file);
+                }
+        }
+
+        return dso;
+}