bfd/dwarf: Improve use of previously loaded dwarf information

When parsing DWARF data in order to report file/line type error messages
we perform section placement to make section addresses unique within
relocatable object files.

Currently, if we reuse previously loaded (and cached) dwarf data then we
neglect to perform section placement, the result is that the section
addresses will not be unique, and we might, incorrectly associate an
address with the wrong debug information, and so report an incorrect
file and line number.

Further we neglect to check that that bfd for which we are looking up
debug information is actually the bfd for which the previous debug
information was loaded, it is possible that we will reuse previously
loaded debug information for a different bfd.

And finally, due to following of gnu_debuglink links in one bfd to
another, the process of checking that the cached debug information is
valid requires us to track the original bfd in the cached debug
information.  The original debug information here is either the bfd that
we're interested in, not the bfd we finally load the debug information
from.

bfd/ChangeLog:

	* dwarf2.c (struct dwarf2_debug): Add orig_bfd member.
	(_bfd_dwarf2_slurp_debug_info): If stashed debug information does
	not match current bfd, then reload debug information.  Record bfd
	we're loading debug info for in the stash.  If we have debug
	informatin in the cache then perform section placement before
	returning.

ld/ChangeLog:

	* testsuite/ld-elf/dwarf.exp (build_tests): Add new tests.
	* testsuite/ld-elf/dwarf2.err: New file.
	* testsuite/ld-elf/dwarf2a.c: New file.
	* testsuite/ld-elf/dwarf2b.c: New file.
	* testsuite/ld-elf/dwarf3.c: New file.
	* testsuite/ld-elf/dwarf3.err: New file.

bfd/ChangeLog

@@ -1,3 +1,12 @@
+2017-02-16  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* dwarf2.c (struct dwarf2_debug): Add orig_bfd member.
+	(_bfd_dwarf2_slurp_debug_info): If stashed debug information does
+	not match current bfd, then reload debug information.  Record bfd
+	we're loading debug info for in the stash.  If we have debug
+	informatin in the cache then perform section placement before
+	returning.
+
 2017-02-16  Alan Modra  <amodra@gmail.com>
 
 	PR 21000

bfd/dwarf2.c

@@ -100,6 +100,12 @@ struct dwarf2_debug
   /* Pointer to the end of the .debug_info section memory buffer.  */
   bfd_byte *info_ptr_end;
 
+  /* Pointer to the original bfd for which debug was loaded.  This is what
+     we use to compare and so check that the cached debug data is still
+     valid - it saves having to possibly dereference the gnu_debuglink each
+     time.  */
+  bfd *orig_bfd;
+
   /* Pointer to the bfd, section and address of the beginning of the
      section.  The bfd might be different than expected because of
      gnu_debuglink sections.  */
@@ -3897,8 +3903,20 @@ _bfd_dwarf2_slurp_debug_info (bfd *abfd, bfd *debug_bfd,
 
   if (stash != NULL)
     {
-      if (section_vma_same (abfd, stash))
+      if (stash->orig_bfd == abfd
+          && section_vma_same (abfd, stash))
+        {
+          /* Check that we did previously find some debug information
+             before attempting to make use of it.  */
+          if (stash->bfd_ptr != NULL)
+            {
+              if (do_place && !place_sections (abfd, stash))
+                return FALSE;
               return TRUE;
+            }
+
+          return FALSE;
+        }
       _bfd_dwarf2_cleanup_debug_info (abfd, pinfo);
       memset (stash, 0, amt);
     }
@@ -3908,6 +3926,7 @@ _bfd_dwarf2_slurp_debug_info (bfd *abfd, bfd *debug_bfd,
       if (! stash)
 	return FALSE;
     }
+  stash->orig_bfd = abfd;
   stash->debug_sections = debug_sections;
   stash->syms = symbols;
   if (!save_section_vma (abfd, stash))

ld/ChangeLog

@@ -1,3 +1,12 @@
+2017-02-16  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* testsuite/ld-elf/dwarf.exp (build_tests): Add new tests.
+	* testsuite/ld-elf/dwarf2.err: New file.
+	* testsuite/ld-elf/dwarf2a.c: New file.
+	* testsuite/ld-elf/dwarf2b.c: New file.
+	* testsuite/ld-elf/dwarf3.c: New file.
+	* testsuite/ld-elf/dwarf3.err: New file.
+
 2017-02-16  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* testsuite/lib/ld-lib.exp (run_cc_link_tests): Add warning,

ld/testsuite/ld-elf/dwarf.exp

@@ -49,6 +49,12 @@ set build_tests {
   {"Build libdwarf1.so"
    "-s -shared" "-fPIC -g -feliminate-dwarf2-dups"
    {dwarf1.c} {} "libdwarf1.so"}
+  {"DWARF parse during linker error"
+   "" "-fno-toplevel-reorder"
+   {dwarf2a.c dwarf2b.c} {{error_output "dwarf2.err"}} "dwarf2.x"}
+  {"Handle no DWARF information"
+   "" "-g0"
+   {dwarf3.c} {{error_output "dwarf3.err"}} "dwarf3.x"}
 }
 
 set run_tests {

ld/testsuite/ld-elf/dwarf2.err

@@ -0,0 +1,4 @@
+tmpdir/dwarf2b\.o:\(\.data\+0x0\): multiple definition of `global_var'
+tmpdir/dwarf2a\.o:\(\.data\+0x0\): first defined here
+tmpdir/dwarf2b\.o:\(\.data\+0x4\): multiple definition of `other_var'
+tmpdir/dwarf2a\.o:\(\.data\+0x4\): first defined here

ld/testsuite/ld-elf/dwarf2a.c

@@ -0,0 +1,8 @@
+int global_var = 3;
+int other_var = 4;
+
+int
+function (void)
+{
+  return 0;
+}

ld/testsuite/ld-elf/dwarf2b.c

@@ -0,0 +1,10 @@
+int global_var = 4;
+int other_var = 2;
+
+extern int function (void);
+
+int
+main ()
+{
+  return function ();
+}

ld/testsuite/ld-elf/dwarf3.c

@@ -0,0 +1,13 @@
+/* This test is actually used to test for a segfault that came from the bfd
+   dwarf parsing code in the case when there is _no_ dwarf info.  */
+
+extern void bar (int a);
+
+int
+main ()
+{
+  bar (1);
+  bar (2);
+
+  return 0;
+}

ld/testsuite/ld-elf/dwarf3.err

@@ -0,0 +1,4 @@
+.*/dwarf3\.o: In function `main':
+.*dwarf3.c:\(\.text.*\+0x[0-9a-f]+\): undefined reference to `bar'
+.*dwarf3.c:\(\.text.*\+0x[0-9a-f]+\): undefined reference to `bar'
+#...