Re: gas emits incorrect .debug_line prologue header length for 64-bit DWARF

[Alan Modra <amodra@gmail.com>]

On Thu, Feb 27, 2014 at 01:03:23PM -0500, Ed Maste wrote:
> The header_length field is supposed to be the number of bytes
> following the field to the first byte of the line number program, but
> dwarf2dbg.c:out_debug_line has hard-coded constants that are correct
> only for 32-bit DWARF.
> 
> I've fixed it in FreeBSD here in SVN r256692:
> http://svnweb.freebsd.org/base?view=revision&revision=256692

Thanks for the heads-up.  I'm committing the following to mainline
that calculates the length as a simple difference of two symbols.

	* dwarf2dbg.c (out_debug_line): Correct .debug_line header_length
	field for 64-bit dwarf.

diff --git a/gas/dwarf2dbg.c b/gas/dwarf2dbg.c
index 6d6ee2d..ac6148f 100644
--- a/gas/dwarf2dbg.c
+++ b/gas/dwarf2dbg.c
@@ -1515,7 +1515,7 @@ static void
 out_debug_line (segT line_seg)
 {
   expressionS exp;
-  symbolS *prologue_end;
+  symbolS *prologue_start, *prologue_end;
   symbolS *line_end;
   struct line_seg *s;
   int sizeof_offset;
@@ -1527,10 +1527,14 @@ out_debug_line (segT line_seg)
   out_two (DWARF2_LINE_VERSION);
 
   /* Length of the prologue following this length.  */
+  prologue_start = symbol_temp_make ();
   prologue_end = symbol_temp_make ();
+  exp.X_op = O_subtract;
   exp.X_add_symbol = prologue_end;
-  exp.X_add_number = - (4 + 2 + 4);
+  exp.X_op_symbol = prologue_start;
+  exp.X_add_number = 0;
   emit_expr (&exp, sizeof_offset);
+  symbol_set_value_now (prologue_start);
 
   /* Parameters of the state machine.  */
   out_byte (DWARF2_LINE_MIN_INSN_LENGTH);

-- 
Alan Modra
Australia Development Lab, IBM