perf symbols: Filename__read_build_id should look at .notes section too

In the kernel we have more than one notes section, so the linker
script combines all and puts them into a ".notes" combined
section. So we need to look at both sections and also traverse
them looking at multiple GElf_Nhdr entries till we find the one
we want, with the build_id.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1258757489-5978-2-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 38 insertions, 9 deletions

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 3b23c18cd36b..d22030828c21 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -899,13 +899,19 @@ bool dsos__read_build_ids(void)
         return have_build_id;
 }
 
+/*
+ * Align offset to 4 bytes as needed for note name and descriptor data.
+ */
+#define NOTE_ALIGN(n) (((n) + 3) & -4U)
+
 int filename__read_build_id(const char *filename, void *bf, size_t size)
 {
         int fd, err = -1;
         GElf_Ehdr ehdr;
         GElf_Shdr shdr;
-        Elf_Data *build_id_data;
+        Elf_Data *data;
         Elf_Scn *sec;
+        void *ptr;
         Elf *elf;
 
         if (size < BUILD_ID_SIZE)
@@ -928,14 +934,37 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 
         sec = elf_section_by_name(elf, &ehdr, &shdr,
                                   ".note.gnu.build-id", NULL);
-        if (sec == NULL)
-                goto out_elf_end;
+        if (sec == NULL) {
+                sec = elf_section_by_name(elf, &ehdr, &shdr,
+                                          ".notes", NULL);
+                if (sec == NULL)
+                        goto out_elf_end;
+        }
 
-        build_id_data = elf_getdata(sec, NULL);
-        if (build_id_data == NULL)
+        data = elf_getdata(sec, NULL);
+        if (data == NULL)
                 goto out_elf_end;
-        memcpy(bf, build_id_data->d_buf + 16, BUILD_ID_SIZE);
-        err = BUILD_ID_SIZE;
+
+        ptr = data->d_buf;
+        while (ptr < (data->d_buf + data->d_size)) {
+                GElf_Nhdr *nhdr = ptr;
+                int namesz = NOTE_ALIGN(nhdr->n_namesz),
+                    descsz = NOTE_ALIGN(nhdr->n_descsz);
+                const char *name;
+
+                ptr += sizeof(*nhdr);
+                name = ptr;
+                ptr += namesz;
+                if (nhdr->n_type == NT_GNU_BUILD_ID &&
+                    nhdr->n_namesz == sizeof("GNU")) {
+                        if (memcmp(name, "GNU", sizeof("GNU")) == 0) {
+                                memcpy(bf, ptr, BUILD_ID_SIZE);
+                                err = BUILD_ID_SIZE;
+                                break;
+                        }
+                }
+                ptr += descsz;
+        }
 out_elf_end:
         elf_end(elf);
 out_close:
@@ -963,8 +992,8 @@ int sysfs__read_build_id(const char *filename, void *build_id, size_t size)
                 if (read(fd, &nhdr, sizeof(nhdr)) != sizeof(nhdr))
                         break;
 
-                namesz = (nhdr.n_namesz + 3) & -4U;
-                descsz = (nhdr.n_descsz + 3) & -4U;
+                namesz = NOTE_ALIGN(nhdr.n_namesz);
+                descsz = NOTE_ALIGN(nhdr.n_descsz);
                 if (nhdr.n_type == NT_GNU_BUILD_ID &&
                     nhdr.n_namesz == sizeof("GNU")) {
                         if (read(fd, bf, namesz) != namesz)