PR ld/16787, stale dwarf2 stash

[Alan Modra <amodra at gmail dot com>]

As the comment I added here says:
  "If find_nearest_line is used in linker warnings or
   errors early in the link process, the debug info stash will be
   invalid for later calls.  This is because we relocate debug info
   sections, so the stashed section contents depend on symbol values,
   which in turn depend on section VMAs."

In fact, VMAs will change multiple times during linking.  Initially
they are zero (usually, for ELF).  After mapping input to output
sections the effective VMA for input sections might be non-zero even
though the output section VMA is still zero.  eg. multiple .text.*
sections in a single object mapping to .text.  After placement the
output section VMAs change, and of course relaxation might change them
yet again.

So, throw away the dwarf2 stash if it becomes invalid due to section
VMAs changing.  It would be nice to reclaim all the bfd_alloc
memory here when we throw away the stash, perhaps by putting
everything we alloc on a private dwarf2 objalloc, but I haven't done
that with this patch.

I've also fixed a problem with bfd_perform_relocation losing reloc
addends, which meant a second or subsequent look at debug info
sections did not properly relocate the sections.  I can't see why
bfd_perform_relocation should need to change addends except for ld -r,
and the history (985fca12, e98e6ec1) doesn't help much.

Finally, the patch tweaks place_sections to avoid unnecessary work.
If we've mapped input to output sections, then input section VMA
isn't used so there's not much point in adjusting it.  Incidentally,
this also means place_sections isn't effective in all cases.

	PR ld/16787
	* dwarf2.c (struct dwarf2_debug): Add sec_vma field.
	(place_sections): Do not modify VMA of sections when called from
	linker after sections have been placed in output sections.  Short
	circuit single section case.
	(save_section_vma, section_vma_same): New functions.
	(_bfd_dwarf2_slurp_debug_info): Throw away stash if section VMAs
	change.
	* reloc.c (bfd_perform_relocation): Do not modify reloc addend
	when non-relocatable.

diff --git a/bfd/dwarf2.c b/bfd/dwarf2.c
index 592e325..90d5a05 100644
--- a/bfd/dwarf2.c
+++ b/bfd/dwarf2.c
@@ -156,6 +156,9 @@ struct dwarf2_debug
      use. */
   struct funcinfo *inliner_chain;
 
+  /* Section VMAs at the time the stash was built.  */
+  bfd_vma *sec_vma;
+
   /* Number of sections whose VMA we must adjust.  */
   unsigned int adjusted_section_count;
 
@@ -3031,7 +3034,9 @@ place_sections (bfd *abfd, struct dwarf2_debug *stash)
 	  bfd_size_type sz;
 	  int is_debug_info;
 
-	  if (sect->vma != 0)
+	  if ((sect->output_section != NULL
+	       && sect->output_section != sect)
+	      || sect->vma != 0)
 	    continue;
 
 	  /* We need to adjust the VMAs of any .debug_info sections.
@@ -3053,6 +3058,8 @@ place_sections (bfd *abfd, struct dwarf2_debug *stash)
 
 	  i++;
 	}
+      if (i <= 1)
+	return TRUE;
 
       amt = i * sizeof (struct adjusted_section);
       p = (struct adjusted_section *) bfd_alloc (abfd, amt);
@@ -3067,7 +3074,9 @@ place_sections (bfd *abfd, struct dwarf2_debug *stash)
 	  bfd_size_type sz;
 	  int is_debug_info;
 
-	  if (sect->vma != 0)
+	  if ((sect->output_section != NULL
+	       && sect->output_section != sect)
+	      || sect->vma != 0)
 	    continue;
 
 	  /* We need to adjust the VMAs of any .debug_info sections.
@@ -3341,6 +3350,56 @@ stash_find_line_fast (struct dwarf2_debug *stash,
 				   filename_ptr, linenumber_ptr);
 }
 
+/* Save current section VMAs.  */
+
+static bfd_boolean
+save_section_vma (const bfd *abfd, struct dwarf2_debug *stash)
+{
+  asection *s;
+  unsigned int i;
+
+  if (abfd->section_count == 0)
+    return TRUE;
+  stash->sec_vma = bfd_malloc (sizeof (*stash->sec_vma) * abfd->section_count);
+  if (stash->sec_vma == NULL)
+    return FALSE;
+  for (i = 0, s = abfd->sections; i < abfd->section_count; i++, s = s->next)
+    {
+      if (s->output_section != NULL)
+	stash->sec_vma[i] = s->output_section->vma + s->output_offset;
+      else
+	stash->sec_vma[i] = s->vma;
+    }
+  return TRUE;
+}
+
+/* Compare current section VMAs against those at the time the stash
+   was created.  If find_nearest_line is used in linker warnings or
+   errors early in the link process, the debug info stash will be
+   invalid for later calls.  This is because we relocate debug info
+   sections, so the stashed section contents depend on symbol values,
+   which in turn depend on section VMAs.  */
+
+static bfd_boolean
+section_vma_same (const bfd *abfd, const struct dwarf2_debug *stash)
+{
+  asection *s;
+  unsigned int i;
+
+  for (i = 0, s = abfd->sections; i < abfd->section_count; i++, s = s->next)
+    {
+      bfd_vma vma;
+
+      if (s->output_section != NULL)
+	vma = s->output_section->vma + s->output_offset;
+      else
+	vma = s->vma;
+      if (vma != stash->sec_vma[i])
+	return FALSE;
+    }
+  return TRUE;
+}
+
 /* Read debug information from DEBUG_BFD when DEBUG_BFD is specified.
    If DEBUG_BFD is not specified, we read debug information from ABFD
    or its gnu_debuglink. The results will be stored in PINFO.
@@ -3358,13 +3417,26 @@ _bfd_dwarf2_slurp_debug_info (bfd *abfd, bfd *debug_bfd,
   struct dwarf2_debug *stash = (struct dwarf2_debug *) *pinfo;
 
   if (stash != NULL)
-    return TRUE;
-
-  stash = (struct dwarf2_debug *) bfd_zalloc (abfd, amt);
-  if (! stash)
-    return FALSE;
+    {
+      if (stash->syms == symbols
+	  && section_vma_same (abfd, stash))
+	return TRUE;
+      _bfd_dwarf2_cleanup_debug_info (abfd, pinfo);
+      memset (stash, 0, amt);
+    }
+  else
+    {
+      stash = (struct dwarf2_debug *) bfd_zalloc (abfd, amt);
+      if (! stash)
+	return FALSE;
+    }
   stash->debug_sections = debug_sections;
   stash->syms = symbols;
+  if (!save_section_vma (abfd, stash))
+    {
+      free (stash);
+      return FALSE;
+    }
 
   *pinfo = stash;
 
@@ -3891,6 +3963,8 @@ _bfd_dwarf2_cleanup_debug_info (bfd *abfd, void **pinfo)
     free (stash->alt_dwarf_str_buffer);
   if (stash->alt_dwarf_info_buffer)
     free (stash->alt_dwarf_info_buffer);
+  if (stash->sec_vma)
+    free (stash->sec_vma);
   if (stash->alt_bfd_ptr)
     bfd_close (stash->alt_bfd_ptr);
 }
diff --git a/bfd/reloc.c b/bfd/reloc.c
index 7ca3cfd..6b1b26e 100644
--- a/bfd/reloc.c
+++ b/bfd/reloc.c
@@ -784,10 +784,6 @@ space consuming.  For each target:
 	    }
 	}
     }
-  else
-    {
-      reloc_entry->addend = 0;
-    }
 
   /* FIXME: This overflow checking is incomplete, because the value
      might have overflowed before we get here.  For a correct check we

-- 
Alan Modra
Australia Development Lab, IBM