perf symbol: Fix symbol parsing in certain cases: use the build-id as a symlink

In some cases distros have binaries and debuginfo in weird places:

[root@doppio tuna]# ls -la /usr/lib64/{xulrunner-1.9.1/xulrunner-stub,firefox-3.5.2/firefox}
-rwxr-xr-x 1 root root 90024 2009-08-03 19:45 /usr/lib64/firefox-3.5.2/firefox
-rwxr-xr-x 1 root root 90024 2009-08-03 18:23 /usr/lib64/xulrunner-1.9.1/xulrunner-stub
[root@doppio tuna]# sha1sum /usr/lib64/{xulrunner-1.9.1/xulrunner-stub,firefox-3.5.2/firefox}
19a858077d263d5de22c9c5da250d3e4396ae739  /usr/lib64/xulrunner-1.9.1/xulrunner-stub
19a858077d263d5de22c9c5da250d3e4396ae739  /usr/lib64/firefox-3.5.2/firefox
[root@doppio tuna]# rpm -qf /usr/lib64/{xulrunner-1.9.1/xulrunner-stub,firefox-3.5.2/firefox}
xulrunner-1.9.1.2-1.fc11.x86_64
firefox-3.5.2-2.fc11.x86_64
[root@doppio tuna]# ls -la /usr/lib/debug/{usr/lib64/xulrunner-1.9.1/xulrunner-stub,usr/lib64/firefox-3.5.2/firefox}.debug
ls: cannot access /usr/lib/debug/usr/lib64/firefox-3.5.2/firefox.debug: No such file or directory
-rwxr-xr-x 1 root root 403608 2009-08-03 18:22 /usr/lib/debug/usr/lib64/xulrunner-1.9.1/xulrunner-stub.debug

Seemingly we don't have a .symtab when we actually can find it
if we use the .note.gnu.build-id ELF section put in place by
some distros. Use it and find the symbols we need.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 0580b94..16ddca2 100644 (file)
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -661,10 +661,69 @@ out_close:
        return err;
 }
 
+#define BUILD_ID_SIZE 128
+
+static char *dso__read_build_id(struct dso *self, int verbose)
+{
+       int i;
+       GElf_Ehdr ehdr;
+       GElf_Shdr shdr;
+       Elf_Data *build_id_data;
+       Elf_Scn *sec;
+       char *build_id = NULL, *bid;
+       unsigned char *raw;
+       Elf *elf;
+       int fd = open(self->name, O_RDONLY);
+
+       if (fd < 0)
+               goto out;
+
+       elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
+       if (elf == NULL) {
+               if (verbose)
+                       fprintf(stderr, "%s: cannot read %s ELF file.\n",
+                               __func__, self->name);
+               goto out_close;
+       }
+
+       if (gelf_getehdr(elf, &ehdr) == NULL) {
+               if (verbose)
+                       fprintf(stderr, "%s: cannot get elf header.\n", __func__);
+               goto out_elf_end;
+       }
+
+       sec = elf_section_by_name(elf, &ehdr, &shdr, ".note.gnu.build-id", NULL);
+       if (sec == NULL)
+               goto out_elf_end;
+
+       build_id_data = elf_getdata(sec, NULL);
+       if (build_id_data == NULL)
+               goto out_elf_end;
+       build_id = malloc(BUILD_ID_SIZE);
+       if (build_id == NULL)
+               goto out_elf_end;
+       raw = build_id_data->d_buf + 16;
+       bid = build_id;
+
+       for (i = 0; i < 20; ++i) {
+               sprintf(bid, "%02x", *raw);
+               ++raw;
+               bid += 2;
+       }
+       if (verbose)
+               printf("%s(%s): %s\n", __func__, self->name, build_id);
+out_elf_end:
+       elf_end(elf);
+out_close:
+       close(fd);
+out:
+       return build_id;
+}
+
 int dso__load(struct dso *self, symbol_filter_t filter, int verbose)
 {
-       int size = strlen(self->name) + sizeof("/usr/lib/debug%s.debug");
-       char *name = malloc(size);
+       int size = PATH_MAX;
+       char *name = malloc(size), *build_id = NULL;
        int variant = 0;
        int ret = -1;
        int fd;
@@ -686,7 +745,18 @@ more:
                case 1: /* Ubuntu */
                        snprintf(name, size, "/usr/lib/debug%s", self->name);
                        break;
-               case 2: /* Sane people */
+               case 2:
+                       build_id = dso__read_build_id(self, verbose);
+                       if (build_id != NULL) {
+                               snprintf(name, size,
+                                        "/usr/lib/debug/.build-id/%.2s/%s.debug",
+                                       build_id, build_id + 2);
+                               free(build_id);
+                               break;
+                       }
+                       variant++;
+                       /* Fall thru */
+               case 3: /* Sane people */
                        snprintf(name, size, "%s", self->name);
                        break;