[COMMITTED] readelf: Fix crash on reading loc data or range data with bad/no CUs.

[Mark Wielaard <mark@klomp.org>]

In print_debug_ranges_section and print_debug_loc_section we try to
get the associated CU through skip_listptr_hole for the first data data.
If no CU at all can be found (because the .debug_info section was bogus)
this would keep the Dwarf_CU uninitialized causing a crash later on
when it was compared to the last_cu and used because it was unequal.
Fix this by explicitly initializing cu to last_cu (which is NULL on
first use).

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 src/ChangeLog | 5 +++++
 src/readelf.c | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/ChangeLog b/src/ChangeLog
index 49b0cc0..a0bb7a2 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2018-01-25  Mark Wielaard  <mark@klomp.org>
+
+	* readelf.c (print_debug_ranges_section): Initialize cu to last_cu.
+	(print_debug_loc_section): Likewise.
+
 2018-01-01  Mark Wielaard  <mark@klomp.org>
 
 	* readelf.c (attr_callback): Use dwarf_form_name for unknown forms.
diff --git a/src/readelf.c b/src/readelf.c
index 4bdaef2..6c49d30 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -5014,7 +5014,7 @@ print_debug_ranges_section (Dwfl_Module *dwflmod,
   while (readp < endp)
     {
       ptrdiff_t offset = readp - (unsigned char *) data->d_buf;
-      Dwarf_CU *cu;
+      Dwarf_CU *cu = last_cu;
 
       if (first && skip_listptr_hole (&known_rangelistptr, &listptr_idx,
 				      &address_size, NULL, &base, &cu,
@@ -7140,7 +7140,7 @@ print_debug_loc_section (Dwfl_Module *dwflmod,
   while (readp < endp)
     {
       ptrdiff_t offset = readp - (unsigned char *) data->d_buf;
-      Dwarf_CU *cu;
+      Dwarf_CU *cu = last_cu;
 
       if (first && skip_listptr_hole (&known_loclistptr, &listptr_idx,
 				      &address_size, &offset_size, &base,
-- 
1.8.3.1