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>

1 files changed, 73 insertions, 3 deletions

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 0580b94785e7..16ddca202948 100644
--- 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;