[PATCH 6/7] [gas] dwarf2: Pad size of .debug_line section.

[Christian Eggers <ceggers at gmx dot de>]

As all dwarf debug information is organized in octets, the size of all
dwarf sections must be aligned to OCTETS_PER_BYTE. Most DWARF sections
meet this requirement, only the .debug_line section can reach an
arbitrary octet size.

In order to align the size to a multiple of OCTETS_PER_BYTE, the section
is padded with "nop" statements at the end.

This change should not affect existing targets as all targets currently
using DWARF2 have 8 bit per byte.

Signed-off-by: Christian Eggers <ceggers@gmx.de>
---
 gas/ChangeLog   |  4 ++++
 gas/dwarf2dbg.c | 14 ++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/gas/ChangeLog b/gas/ChangeLog
index 2d7dabc299..c6a857b93c 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,7 @@
+2019-03-10  Christian Eggers  <ceggers@gmx.de>
+
+	* dwarf2dbg.c (out_debug_line): Pad size of .debug_line section.
+
 2019-03-10  Christian Eggers  <ceggers@gmx.de>
 
 	* dwarf2dbg.c: Use octets for .debug_string pointers.
diff --git a/gas/dwarf2dbg.c b/gas/dwarf2dbg.c
index d469138576..9e68233ad3 100644
--- a/gas/dwarf2dbg.c
+++ b/gas/dwarf2dbg.c
@@ -1787,6 +1787,7 @@ out_debug_line (segT line_seg)
   symbolS *line_end;
   struct line_seg *s;
   int sizeof_offset;
+  addressT section_end, section_end_aligned;
 
   memset (&exp, 0, sizeof exp);
   sizeof_offset = out_header (line_seg, &exp);
@@ -1848,6 +1849,19 @@ out_debug_line (segT line_seg)
        in the DWARF Line Number header.  */
     subseg_set (subseg_get (".debug_line_end", FALSE), 0);
 
+  /* Pad size of .debug_line section to a multiple of OCTETS_PER_BYTE. Simply
+     sizing the section in md_section_align() is not sufficient, also the size
+     field in the .debug_line header must be a multiple of OCTETS_PER_BYTE. Not
+     doing so will introduce gaps within the .debug_line sections after linking.
+       */
+  section_end = frag_now_fix_octets ();
+  section_end_aligned = (section_end + OCTETS_PER_BYTE - 1) &
+                        ~(OCTETS_PER_BYTE  - 1);
+  for ( ; section_end != section_end_aligned; section_end++)
+    {
+      out_inc_line_addr (0, 0);  /* NOP */
+    }
+
   symbol_set_value_now_octets (line_end);
 }
 
-- 
2.16.4