bfd: Improve lookup of file / line information for errors

When looking up file and line information (used from the linker to
report error messages) if no symbol is passed in, then use the symbol
list to look for a matching symbol.

If a matching symbol is found then use this to look up the file / line
information.

This should improve errors when looking up file / line information for
data sections.  Hopefully we should find a matching data symbol, which
should, in turn (we hope) match a DW_TAG_variable in the DWARF, this
should allow us to give accurate file / line errors for data symbols.

As the hope is to find a matching DW_TAG_variable in the DWARF then we
ignore section symbols, and prefer global symbols to locals.

bfd/ChangeLog:

	* dwarf2.c (_bfd_dwarf2_find_nearest_line): Perform symbol lookup
	before trying to fine matching file and line information.

ld/ChangeLog:

	* testsuite/ld-elf/shared.exp: Update expected results.
	* testsuite/ld-elf/dwarf2.err: Likewise

2 files changed, 37 insertions, 0 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 01314bd..40edca7 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,5 +1,10 @@
 2017-02-16  Andrew Burgess  <andrew.burgess@embecosm.com>
 
+	* dwarf2.c (_bfd_dwarf2_find_nearest_line): Perform symbol lookup
+	before trying to fine matching file and line information.
+
+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
diff --git a/bfd/dwarf2.c b/bfd/dwarf2.c
index 03447a9..9bb8126 100644
--- a/bfd/dwarf2.c
+++ b/bfd/dwarf2.c
@@ -4155,6 +4155,38 @@ _bfd_dwarf2_find_nearest_line (bfd *abfd,
     {
       BFD_ASSERT (section != NULL && functionname_ptr != NULL);
       addr = offset;
+
+      /* If we have no SYMBOL but the section we're looking at is not a
+         code section, then take a look through the list of symbols to see
+         if we have a symbol at the address we're looking for.  If we do
+         then use this to look up line information.  This will allow us to
+         give file and line results for data symbols.  We exclude code
+         symbols here, if we look up a function symbol and then look up the
+         line information we'll actually return the line number for the
+         opening '{' rather than the function definition line.  This is
+         because looking up by symbol uses the line table, in which the
+         first line for a function is usually the opening '{', while
+         looking up the function by section + offset uses the
+         DW_AT_decl_line from the function DW_TAG_subprogram for the line,
+         which will be the line of the function name.  */
+      if ((section->flags & SEC_CODE) == 0)
+	{
+	  asymbol **tmp;
+
+	  for (tmp = symbols; (*tmp) != NULL; ++tmp)
+	    if ((*tmp)->the_bfd == abfd
+		&& (*tmp)->section == section
+		&& (*tmp)->value == offset
+		&& ((*tmp)->flags & BSF_SECTION_SYM) == 0)
+	      {
+		symbol = *tmp;
+		do_line = TRUE;
+                /* For local symbols, keep going in the hope we find a
+                   global.  */
+                if ((symbol->flags & BSF_GLOBAL) != 0)
+                  break;
+	      }
+	}
     }
 
   if (section->output_section)