perf symbols: Follow .gnu_debuglink section to find separate symbols

The .gnu_debuglink section is specified to contain the filename of the
debug info file, as well as a CRC that can be used to validate it.

This doesn't currently use the checksum and relies on the usual build-id
matching for validation.

This provides more context:
http://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html

Signed-off-by: Pierre-Loup A. Griffais <pgriffais@nvidia.com>
Reported-by: Mike Sartain <mikesart@valvesoftware.com>
Tested-by: Mike Sartain <mikesart@valvesoftware.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Sartain <mikesart@valvesoftware.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/4FE4BB95.3080309@nvidia.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 65 insertions, 1 deletions

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 3e2e5ea0f03f..994f4ffdcd05 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1590,11 +1590,62 @@ out:
         return err;
 }
 
+static int filename__read_debuglink(const char *filename,
+                                    char *debuglink, size_t size)
+{
+        int fd, err = -1;
+        Elf *elf;
+        GElf_Ehdr ehdr;
+        GElf_Shdr shdr;
+        Elf_Data *data;
+        Elf_Scn *sec;
+        Elf_Kind ek;
+
+        fd = open(filename, O_RDONLY);
+        if (fd < 0)
+                goto out;
+
+        elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
+        if (elf == NULL) {
+                pr_debug2("%s: cannot read %s ELF file.\n", __func__, filename);
+                goto out_close;
+        }
+
+        ek = elf_kind(elf);
+        if (ek != ELF_K_ELF)
+                goto out_close;
+
+        if (gelf_getehdr(elf, &ehdr) == NULL) {
+                pr_err("%s: cannot get elf header.\n", __func__);
+                goto out_close;
+        }
+
+        sec = elf_section_by_name(elf, &ehdr, &shdr,
+                                  ".gnu_debuglink", NULL);
+        if (sec == NULL)
+                goto out_close;
+
+        data = elf_getdata(sec, NULL);
+        if (data == NULL)
+                goto out_close;
+
+        /* the start of this section is a zero-terminated string */
+        strncpy(debuglink, data->d_buf, size);
+
+        elf_end(elf);
+
+out_close:
+        close(fd);
+out:
+        return err;
+}
+
 char dso__symtab_origin(const struct dso *dso)
 {
         static const char origin[] = {
                 [SYMTAB__KALLSYMS]            = 'k',
                 [SYMTAB__JAVA_JIT]            = 'j',
+                [SYMTAB__DEBUGLINK]           = 'l',
                 [SYMTAB__BUILD_ID_CACHE]      = 'B',
                 [SYMTAB__FEDORA_DEBUGINFO]    = 'f',
                 [SYMTAB__UBUNTU_DEBUGINFO]    = 'u',
@@ -1662,10 +1713,22 @@ int dso__load(struct dso *dso, struct map *map, symbol_filter_t filter)
          */
         want_symtab = 1;
 restart:
-        for (dso->symtab_type = SYMTAB__BUILD_ID_CACHE;
+        for (dso->symtab_type = SYMTAB__DEBUGLINK;
              dso->symtab_type != SYMTAB__NOT_FOUND;
              dso->symtab_type++) {
                 switch (dso->symtab_type) {
+                case SYMTAB__DEBUGLINK: {
+                        char *debuglink;
+                        strncpy(name, dso->long_name, size);
+                        debuglink = name + dso->long_name_len;
+                        while (debuglink != name && *debuglink != '/')
+                                debuglink--;
+                        if (*debuglink == '/')
+                                debuglink++;
+                        filename__read_debuglink(dso->long_name, debuglink,
+                                                 size - (debuglink - name));
+                        }
+                        break;
                 case SYMTAB__BUILD_ID_CACHE:
                         /* skip the locally configured cache if a symfs is given */
                         if (symbol_conf.symfs[0] ||
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index af0752b1aca1..a884b99017f0 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -257,6 +257,7 @@ enum symtab_type {
         SYMTAB__KALLSYMS = 0,
         SYMTAB__GUEST_KALLSYMS,
         SYMTAB__JAVA_JIT,
+        SYMTAB__DEBUGLINK,
         SYMTAB__BUILD_ID_CACHE,
         SYMTAB__FEDORA_DEBUGINFO,
         SYMTAB__UBUNTU_DEBUGINFO,