[gdb patch] seg fault on missing dwarf

[Nathan Sidwell <nathan@acm.org>]

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Pedro,
this is Alex's patch of 
https://sourceware.org/ml/gdb-patches/2017-09/msg00745.html cleaned up 
with changelog formatting.  Alex is a fellow FaceBooker.

The patch looks obvious to me, particularly as a few lines down we have:

       fprintf_unfiltered (gdb_stdlog,
			  "    %s CUs, %s TUs\n",
			  pulongest (dwp_file->cus ? dwp_file->cus->nr_units : 0),
			  pulongest (dwp_file->tus ? dwp_file->tus->nr_units : 0));

to protect dump output from exactly this problem.

ok?

nathan
-- 
Nathan Sidwell

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2017-09-25  Alexander Shaposhnikov <alexander.v.shaposhnikov@gmail.com>
	
	* dwarf2read.c (open_and_init_dwp_file): Protect against dwp_file
	having NULL cus or tus.

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index b1914cf..547e3f0 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -11185,7 +11185,8 @@ open_and_init_dwp_file (void)
   dwp_file->tus = create_dwp_hash_table (dwp_file, 1);
 
   /* The DWP file version is stored in the hash table.  Oh well.  */
-  if (dwp_file->cus->version != dwp_file->tus->version)
+  if (dwp_file->cus && dwp_file->tus
+      && dwp_file->cus->version != dwp_file->tus->version)
     {
       /* Technically speaking, we should try to limp along, but this is
 	 pretty bizarre.  We use pulongest here because that's the established
@@ -11195,7 +11196,7 @@ open_and_init_dwp_file (void)
 	     pulongest (dwp_file->cus->version),
 	     pulongest (dwp_file->tus->version), dwp_name.c_str ());
     }
-  dwp_file->version = dwp_file->cus->version;
+  dwp_file->version = dwp_file->cus ? dwp_file->cus->version : 0;
 
   if (dwp_file->version == 2)
     bfd_map_over_sections (dwp_file->dbfd, dwarf2_locate_v2_dwp_sections,