Add .nop assembler directive

Implement the '.nop SIZE[, CONTROL]' assembler directive, which emits
SIZE bytes filled with no-op instructions.  SIZE is absolute expression.
The optional CONTROL byte controls how no-op instructions should be
generated.  If the comma and @var{control} are omitted, CONTROL is
assumed to be zero.

For Intel 80386 and AMD x86-64 targets, CONTROL byte specifies the size
limit of a single no-op instruction.  The valid values of CONTROL byte
are between 0 and 8 for 16-bit mode, between 0 and 10 for 32-bit mode,
between 0 and 11 for 64-bit mode.  When 0 is used, the no-op size limit
is set to the maximum supported size.

2 new relax states, rs_space_nop and rs_fill_nop, are added to enum
_relax_state, which are similar to rs_space and rs_fill, respectively,
but they fill with no-op instructions, instead of a single byte.  A
target backend must override the default md_generate_nops to generate
proper no-op instructions.  Otherwise, an error of unimplemented .nop
directive will be issued whenever .nop directive is used.

	* NEWS: Mention .nop directive.
	* as.h (_relax_state): Add rs_space_nop and rs_fill_nop.
	* read.c (potable): Add .nop.
	(s_nop): New function.
	* read.h (s_nop): New prototype.
	* write.c (cvt_frag_to_fill): Handle rs_space_nop and
	rs_fill_nop.
	(md_generate_nops): New function.
	(relax_segment): Likewise.
	(write_contents): Use md_generate_nops for rs_fill_nop.
	* config/tc-i386.c (alt64_11): New.
	(alt64_patt): Likewise.
	(md_convert_frag): Handle rs_space_nop.
	(i386_output_nops): New function.
	(i386_generate_nops): Likewise.
	(i386_align_code): Call i386_output_nops.
	* config/tc-i386.h (i386_generate_nops): New.
	(md_generate_nops): Likewise.
	* doc/as.texinfo: Document .nop directive.
	* testsuite/gas/i386/i386.exp: Run .nop directive tests.
	* testsuite/gas/i386/nop-1.d: New file.
	* testsuite/gas/i386/nop-1.s: Likewise.
	* testsuite/gas/i386/nop-2.d: Likewise.
	* testsuite/gas/i386/nop-2.s: Likewise.
	* testsuite/gas/i386/nop-3.d: Likewise.
	* testsuite/gas/i386/nop-3.s: Likewise.
	* testsuite/gas/i386/nop-4.d: Likewise.
	* testsuite/gas/i386/nop-4.s: Likewise.
	* testsuite/gas/i386/nop-5.d: Likewise.
	* testsuite/gas/i386/nop-5.s: Likewise.
	* testsuite/gas/i386/nop-6.d: Likewise.
	* testsuite/gas/i386/nop-6.s: Likewise.
	* testsuite/gas/i386/nop-bad-1.l: Likewise.
	* testsuite/gas/i386/nop-bad-1.s: Likewise.
	* testsuite/gas/i386/x86-64-nop-1.d: Likewise.
	* testsuite/gas/i386/x86-64-nop-2.d: Likewise.
	* testsuite/gas/i386/x86-64-nop-3.d: Likewise.
	* testsuite/gas/i386/x86-64-nop-4.d: Likewise.
	* testsuite/gas/i386/x86-64-nop-5.d: Likewise.
	* testsuite/gas/i386/x86-64-nop-6.d: Likewise.

1 files changed, 53 insertions, 0 deletions

diff --git a/gas/read.c b/gas/read.c
index 7bf52f1..9ab88f8 100644
--- a/gas/read.c
+++ b/gas/read.c
@@ -442,6 +442,7 @@ static const pseudo_typeS potable[] = {
 /* size  */
   {"space", s_space, 0},
   {"skip", s_space, 0},
+  {"nop", s_nop, 0},
   {"sleb128", s_leb128, 1},
   {"spc", s_ignore, 0},
   {"stabd", s_stab, 'd'},
@@ -3508,6 +3509,58 @@ s_space (int mult)
     mri_comment_end (stop, stopc);
 }
 
+void
+s_nop (int ignore ATTRIBUTE_UNUSED)
+{
+  expressionS exp;
+  expressionS val;
+
+#ifdef md_flush_pending_output
+  md_flush_pending_output ();
+#endif
+
+#ifdef md_cons_align
+  md_cons_align (1);
+#endif
+
+  expression (&exp);
+
+  if (*input_line_pointer == ',')
+    {
+      ++input_line_pointer;
+      expression (&val);
+    }
+  else
+    {
+      val.X_op = O_constant;
+      val.X_add_number = 0;
+    }
+
+  if (val.X_op == O_constant)
+    {
+      if (val.X_add_number < 0)
+	{
+	  as_warn (_("negative nop control byte, ignored"));
+	  val.X_add_number = 0;
+	}
+
+      if (!need_pass_2)
+	{
+	  /* Store the no-op instruction control byte in the first byte
+	     of frag.  */
+	  char *p;
+	  symbolS *sym = make_expr_symbol (&exp);
+	  p = frag_var (rs_space_nop, 1, 1, (relax_substateT) 0,
+			sym, (offsetT) 0, (char *) 0);
+	  *p = val.X_add_number;
+	}
+    }
+  else
+    as_bad (_("unsupported variable nop control in .nop directive"));
+
+  demand_empty_rest_of_line ();
+}
+
 /* This is like s_space, but the value is a floating point number with
    the given precision.  This is for the MRI dcb.s pseudo-op and
    friends.  */