perf: parse the .debug_frame section in case .eh_frame is not present

On ARM the debug info is not present in the .eh_frame sections but
in .debug_frame instead, in dwarf format.
Use libunwind to load and parse the debug info.

Dependencies:
 . if present, libunwind >= 1.1 is needed to prevent a segfault when
   parsing the dwarf info,
 . libunwind needs to be configured with --enable-debug-frame. Note:
   --enable-debug-frame is automatically selected on ARM.

Acked-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Jean Pihet <jean.pihet@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 59 insertions, 16 deletions

diff --git a/tools/perf/util/unwind.c b/tools/perf/util/unwind.c
index 2f891f7e70bf..5390d0b8862a 100644
--- a/tools/perf/util/unwind.c
+++ b/tools/perf/util/unwind.c
@@ -39,6 +39,15 @@ UNW_OBJ(dwarf_search_unwind_table) (unw_addr_space_t as,
 
 #define dwarf_search_unwind_table UNW_OBJ(dwarf_search_unwind_table)
 
+extern int
+UNW_OBJ(dwarf_find_debug_frame) (int found, unw_dyn_info_t *di_debug,
+                                 unw_word_t ip,
+                                 unw_word_t segbase,
+                                 const char *obj_name, unw_word_t start,
+                                 unw_word_t end);
+
+#define dwarf_find_debug_frame UNW_OBJ(dwarf_find_debug_frame)
+
 #define DW_EH_PE_FORMAT_MASK    0x0f    /* format of the encoded value */
 #define DW_EH_PE_APPL_MASK      0x70    /* how the value is to be applied */
 
@@ -245,8 +254,9 @@ static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
         return 0;
 }
 
-static int read_unwind_spec(struct dso *dso, struct machine *machine,
-                            u64 *table_data, u64 *segbase, u64 *fde_count)
+static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
+                                     u64 *table_data, u64 *segbase,
+                                     u64 *fde_count)
 {
         int ret = -EINVAL, fd;
         u64 offset;
@@ -255,6 +265,7 @@ static int read_unwind_spec(struct dso *dso, struct machine *machine,
         if (fd < 0)
                 return -EINVAL;
 
+        /* Check the .eh_frame section for unwinding info */
         offset = elf_section_offset(fd, ".eh_frame_hdr");
         close(fd);
 
@@ -263,10 +274,29 @@ static int read_unwind_spec(struct dso *dso, struct machine *machine,
                                           table_data, segbase,
                                           fde_count);
 
-        /* TODO .debug_frame check if eh_frame_hdr fails */
         return ret;
 }
 
+#ifndef NO_LIBUNWIND_DEBUG_FRAME
+static int read_unwind_spec_debug_frame(struct dso *dso,
+                                        struct machine *machine, u64 *offset)
+{
+        int fd = dso__data_fd(dso, machine);
+
+        if (fd < 0)
+                return -EINVAL;
+
+        /* Check the .debug_frame section for unwinding info */
+        *offset = elf_section_offset(fd, ".debug_frame");
+        close(fd);
+
+        if (*offset)
+                return 0;
+
+        return -EINVAL;
+}
+#endif
+
 static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
 {
         struct addr_location al;
@@ -291,20 +321,33 @@ find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
 
         pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
 
-        if (read_unwind_spec(map->dso, ui->machine,
-                             &table_data, &segbase, &fde_count))
-                return -EINVAL;
+        /* Check the .eh_frame section for unwinding info */
+        if (!read_unwind_spec_eh_frame(map->dso, ui->machine,
+                                       &table_data, &segbase, &fde_count)) {
+                memset(&di, 0, sizeof(di));
+                di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
+                di.start_ip = map->start;
+                di.end_ip   = map->end;
+                di.u.rti.segbase    = map->start + segbase;
+                di.u.rti.table_data = map->start + table_data;
+                di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
+                                      / sizeof(unw_word_t);
+                return dwarf_search_unwind_table(as, ip, &di, pi,
+                                                 need_unwind_info, arg);
+        }
+
+#ifndef NO_LIBUNWIND_DEBUG_FRAME
+        /* Check the .debug_frame section for unwinding info */
+        if (!read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
+                memset(&di, 0, sizeof(di));
+                dwarf_find_debug_frame(0, &di, ip, 0, map->dso->name,
+                                       map->start, map->end);
+                return dwarf_search_unwind_table(as, ip, &di, pi,
+                                                 need_unwind_info, arg);
+        }
+#endif
 
-        memset(&di, 0, sizeof(di));
-        di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
-        di.start_ip = map->start;
-        di.end_ip   = map->end;
-        di.u.rti.segbase    = map->start + segbase;
-        di.u.rti.table_data = map->start + table_data;
-        di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
-                              / sizeof(unw_word_t);
-        return dwarf_search_unwind_table(as, ip, &di, pi,
-                                         need_unwind_info, arg);
+        return -EINVAL;
 }
 
 static int access_fpreg(unw_addr_space_t __maybe_unused as,