PR23425, unresolved symbol diagnostic

dwarf2.c code reasonably assumes that debug info is local to a file,
an assumption now violated by gcc, resulting in "DWARF error: invalid
abstract instance DIE ref" or wrong details when attempting to print
linker error messages with file, function and line reported.

This is because find_abstract_instance is only prepared to handle
DW_FORM_ref_addr when the .debug_info section referenced is in the
current file.  When that isn't the case, relocations to access another
file's .debug_info will typically be against a symbol defined at the
start of that .debug_info section, plus an addend.  Since the dwarf2.c
code only considers the current file's debug info, that symbol will be
undefined, resolving to zero.  In effect the ref_addr will wrongly
resolve to the current file's .debug_info.

This patch avoids the problem by treating relocations in debug
sections against undefined symbols in a similar manner to the way
relocations against symbols defined in discarded sections are
resolved.  They result in a zero value (except in .debug_ranges)
regardless of the addend.

	PR 23425
	* reloc.c (bfd_generic_get_relocated_section_contents): Zero reloc
	fields in debug sections when reloc is against an undefined symbol
	and called from bfd_simple_get_relocated_section_contents or
	similar.
	* dwarf2.c (find_abstract_instance): Return true for zero offset
	DW_FORM_ref_addr without returning values.

1 files changed, 3 insertions, 1 deletions

diff --git a/bfd/dwarf2.c b/bfd/dwarf2.c
index 8fadb5c..3b28855 100644
--- a/bfd/dwarf2.c
+++ b/bfd/dwarf2.c
@@ -2837,7 +2837,9 @@ find_abstract_instance (struct comp_unit *   unit,
       info_ptr = unit->stash->info_ptr_memory;
       info_ptr_end = unit->stash->info_ptr_end;
       total = info_ptr_end - info_ptr;
-      if (!die_ref || die_ref >= total)
+      if (!die_ref)
+	return TRUE;
+      else if (die_ref >= total)
 	{
 	  _bfd_error_handler
 	    (_("DWARF error: invalid abstract instance DIE ref"));