perf symbols: Factor out buildid reading routine

So that we can run it without having a DSO instance.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <1257291970-8208-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 36 insertions, 17 deletions

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index ac94d7b94f61..e7c7cdb851c2 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -825,27 +825,27 @@ out_close:
         return err;
 }
 
-#define BUILD_ID_SIZE 128
+#define BUILD_ID_SIZE 20
 
-static char *dso__read_build_id(struct dso *self)
+int filename__read_build_id(const char *filename, void *bf, size_t size)
 {
-        int i;
+        int fd, err = -1;
         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->long_name, O_RDONLY);
 
+        if (size < BUILD_ID_SIZE)
+                goto out;
+
+        fd = open(filename, O_RDONLY);
         if (fd < 0)
                 goto out;
 
         elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
         if (elf == NULL) {
-                pr_err("%s: cannot read %s ELF file.\n", __func__,
-                       self->long_name);
+                pr_err("%s: cannot read %s ELF file.\n", __func__, filename);
                 goto out_close;
         }
 
@@ -854,29 +854,46 @@ static char *dso__read_build_id(struct dso *self)
                 goto out_elf_end;
         }
 
-        sec = elf_section_by_name(elf, &ehdr, &shdr, ".note.gnu.build-id", NULL);
+        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);
+        memcpy(bf, build_id_data->d_buf + 16, BUILD_ID_SIZE);
+        err = BUILD_ID_SIZE;
+out_elf_end:
+        elf_end(elf);
+out_close:
+        close(fd);
+out:
+        return err;
+}
+
+static char *dso__read_build_id(struct dso *self)
+{
+        int i, len;
+        char *build_id = NULL, *bid;
+        unsigned char rawbf[BUILD_ID_SIZE], *raw;
+
+        len = filename__read_build_id(self->long_name, rawbf, sizeof(rawbf));
+        if (len < 0)
+                goto out;
+
+        build_id = malloc(len * 2 + 1);
         if (build_id == NULL)
-                goto out_elf_end;
-        raw = build_id_data->d_buf + 16;
+                goto out;
         bid = build_id;
 
-        for (i = 0; i < 20; ++i) {
+        raw = rawbf;
+        for (i = 0; i < len; ++i) {
                 sprintf(bid, "%02x", *raw);
                 ++raw;
                 bid += 2;
         }
         pr_debug2("%s(%s): %s\n", __func__, self->long_name, build_id);
-out_elf_end:
-        elf_end(elf);
-out_close:
-        close(fd);
 out:
         return build_id;
 }
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index 088433062dd4..e0d4a583f8dd 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -82,6 +82,8 @@ void dsos__fprintf(FILE *fp);
 size_t dso__fprintf(struct dso *self, FILE *fp);
 char dso__symtab_origin(const struct dso *self);
 
+int filename__read_build_id(const char *filename, void *bf, size_t size);
+
 int load_kernel(symbol_filter_t filter);
 
 void symbol__init(unsigned int priv_size);