[PATCH][AArch64][gas] Set the minimum alignment on code segments.

[Matthew Wahab <matthew dot wahab at arm dot com>]

On AArch64, gas doesn't set the minimum alignment for code segments 
making it possible for a segment to become misaligned during a link. It 
is also inconsistent with the ABI (4.3.5: Section Alignment).

This patch sets the minimum alignment for a section to 4 bytes, if the 
section contains an instruction.

A similar issue in the ARM backend has already been fixed 
(https://sourceware.org/bugzilla/show_bug.cgi?id=12931).

Tested aarch64-none-linux-gnu and aarch64-none-elf with check-gas, 
check-ld, check-binutils.

Ok for trunk?
Matthew

gas/
2015-03-05  Matthew Wahab  <matthew.wahab@arm.com>

	* config/tc-aarch64.c (mapping_state): Set minimum alignment for
	code sections.


gas/testsuite
2015-03-05  Matthew Wahab  <matthew.wahab@arm.com>

	* gas/aarch64/codealign.d: Add test for code section alignment.
	* gas/aarch64/codealign.s: New file.

diff --git a/gas/config/tc-aarch64.c b/gas/config/tc-aarch64.c
index 9179fc6..77701c6 100644
--- a/gas/config/tc-aarch64.c
+++ b/gas/config/tc-aarch64.c
@@ -1478,7 +1478,14 @@ mapping_state (enum mstate state)
     /* The mapping symbol has already been emitted.
        There is nothing else to do.  */
     return;
-  else if (TRANSITION (MAP_UNDEFINED, MAP_DATA))
+
+  if (state == MAP_INSN)
+    /* AArch64 instructions require 4-byte alignment.  When emitting
+       instructions into any section, record the appropriate section
+       alignment.  */
+    record_alignment (now_seg, 2);
+
+  if (TRANSITION (MAP_UNDEFINED, MAP_DATA))
     /* This case will be evaluated later in the next else.  */
     return;
   else if (TRANSITION (MAP_UNDEFINED, MAP_INSN))
diff --git a/gas/testsuite/gas/aarch64/codealign.d b/gas/testsuite/gas/aarch64/codealign.d
new file mode 100644
index 0000000..8e75c87
--- /dev/null
+++ b/gas/testsuite/gas/aarch64/codealign.d
@@ -0,0 +1,16 @@
+#objdump: --section-headers 
+# Minimum code alignment should be set.
+# This test is only valid on ELF based ports.
+#not-target: *-*-*coff *-*-pe *-*-wince *-*-*aout* *-*-netbsd *-*-riscix*
+
+.*: +file format.*aarch64.*
+
+Sections:
+Idx Name          Size      VMA               LMA               File off  Algn
+  0 \.text         .*  .*  .*  .*  2\*\*2
+                  .*CODE.*
+  1 \.data         .*  .*  .* .*  2\*\*0
+                  .*DATA.*
+  2 \.bss          .*  .*  .*  .*  2\*\*0
+.*
+
diff --git a/gas/testsuite/gas/aarch64/codealign.s b/gas/testsuite/gas/aarch64/codealign.s
new file mode 100644
index 0000000..b80a6d9
--- /dev/null
+++ b/gas/testsuite/gas/aarch64/codealign.s
@@ -0,0 +1,2 @@
+.text
+  nop