Backport libbacktrace fix to GCC 4.8 branch

[Ian Lance Taylor]

I backported the libbacktrace fix in
http://gcc.gnu.org/ml/gcc-patches/2013-10/msg01445.html to the GCC 4.8
branch.  Bootstrapped and ran libbacktrace testsuite on
x86_64-unknown-linux-gnu.  Committed to 4.8 branch.

Ian


2013-11-30  Ian Lance Taylor  <i...@google.com>

        Backport from mainline:
        2013-10-17  Ian Lance Taylor  <i...@google.com>

        * elf.c (elf_add): Don't get the wrong offsets if a debug section
        is missing.



Index: elf.c
===================================================================
--- elf.c	(revision 205552)
+++ elf.c	(working copy)
@@ -725,6 +725,8 @@ elf_add (struct backtrace_state *state,
     {
       off_t end;
 
+      if (sections[i].size == 0)
+	continue;
       if (min_offset == 0 || sections[i].offset < min_offset)
 	min_offset = sections[i].offset;
       end = sections[i].offset + sections[i].size;
@@ -751,8 +753,13 @@ elf_add (struct backtrace_state *state,
   descriptor = -1;
 
   for (i = 0; i < (int) DEBUG_MAX; ++i)
-    sections[i].data = ((const unsigned char *) debug_view.data
-			+ (sections[i].offset - min_offset));
+    {
+      if (sections[i].size == 0)
+	sections[i].data = NULL;
+      else
+	sections[i].data = ((const unsigned char *) debug_view.data
+			    + (sections[i].offset - min_offset));
+    }
 
   if (!backtrace_dwarf_add (state, base_address,
 			    sections[DEBUG_INFO].data,