libopcodes/aarch64: add support for disassembler styling

This commit enables disassembler styling for AArch64.  After this
commit it is possible to have objdump style AArch64 disassembler
output (using --disassembler-color option).  Once the required GDB
patches are merged, GDB will also style the disassembler output.

The changes to support styling are mostly split between two files
opcodes/aarch64-dis.c and opcodes/aarch64-opc.c.

The entry point for the AArch64 disassembler can be found in
aarch64-dis.c, this file handles printing the instruction mnemonics,
and assembler directives (e.g. '.byte', '.word', etc).  Some operands,
mostly relating to assembler directives are also printed from this
file.  This commit changes all of this to pass through suitable
styling information.

However, for most "normal" instructions, the instruction operands are
printed using a two step process.  From aarch64-dis.c, in the
print_operands function, the function aarch64_print_operand is called,
this function is in aarch64-opc.c, and converts an instruction operand
into a string.  Then, back in print_operands (aarch64-dis.c), the
operand string is printed.

Unfortunately, the string returned by aarch64_print_operand can be
quite complex, it will include syntax elements, like '[' and ']', in
addition to register names and immediate values.  In some cases, a
single operand will expand into what will appear (to the user) as
multiple operands separated with a ','.

This makes the task of styling more complex, all these different
components need to by styled differently, so we need to get the
styling information out of aarch64_print_operand in some way.

The solution that I propose here is similar to the solution that I
used for the i386 disassembler.

Currently, aarch64_print_operand uses snprintf to write the operand
text into a buffer provided by the caller.

What I propose is that we pass an extra argument to the
aarch64_print_operand function, this argument will be a structure, the
structure contains a callback function and some state.

When aarch64_print_operand needs to format part of its output this can
be done by using the callback function within the new structure, this
callback returns a string with special embedded markers that indicate
which mode should be used for each piece of text.  Back in
aarch64-dis.c we can spot these special style markers and use this to
split the disassembler output up and apply the correct style to each
piece.

To make aarch64-opc.c clearer a series of new static functions have
been added, e.g. 'style_reg', 'style_imm', etc.  Each of these
functions formats a piece of text in a different style, 'register' and
'immediate' in this case.

Here's an example taken from aarch64-opc.c of the new functions in
use:

    snprintf (buf, size, "[%s, %s]!",
              style_reg (styler, base),
              style_imm (styler, "#%d", opnd->addr.offset.imm));

The aarch64_print_operand function is also called from the assembler
to aid in printing diagnostic messages.  Right now I have no plans to
add styling to the assembler output, and so, the callback function
used in the assembler ignores the styling information and just returns
an plain string.

I've used the source files in gas/testsuite/gas/aarch64/ for testing,
and have manually gone through and checked that the styling looks
reasonable, however, I'm not an AArch64 expert, so it is possible that
the odd piece is styled incorrectly.  Please point out any mistakes
I've made.

With objdump disassembler color turned off, there should be no change
in the output after this commit.

1 files changed, 215 insertions, 32 deletions

diff --git a/opcodes/aarch64-dis.c b/opcodes/aarch64-dis.c
index acaad28..9e98f0d 100644
--- a/opcodes/aarch64-dis.c
+++ b/opcodes/aarch64-dis.c
@@ -25,9 +25,18 @@
 #include "opintl.h"
 #include "aarch64-dis.h"
 #include "elf-bfd.h"
+#include "safe-ctype.h"
+#include "obstack.h"
+
+#define obstack_chunk_alloc xmalloc
+#define obstack_chunk_free free
 
 #define INSNLEN 4
 
+/* This character is used to encode style information within the output
+   buffers.  See get_style_text and print_operands for more details.  */
+#define STYLE_MARKER_CHAR '\002'
+
 /* Cached mapping symbol state.  */
 enum map_type
 {
@@ -3275,6 +3284,90 @@ aarch64_decode_insn (aarch64_insn insn, aarch64_inst *inst,
   return ERR_UND;
 }
 
+/* Return a short string to indicate a switch to STYLE.  These strings
+   will be embedded into the disassembled operand text (as produced by
+   aarch64_print_operand), and then spotted in the print_operands function
+   so that the disassembler output can be split by style.  */
+
+static const char *
+get_style_text (enum disassembler_style style)
+{
+  static bool init = false;
+  static char formats[16][4];
+  unsigned num;
+
+  /* First time through we build a string for every possible format.  This
+     code relies on there being no more than 16 different styles (there's
+     an assert below for this).  */
+  if (!init)
+    {
+      int i;
+
+      for (i = 0; i <= 0xf; ++i)
+	{
+	  int res = snprintf (&formats[i][0], sizeof (formats[i]), "%c%x%c",
+			      STYLE_MARKER_CHAR, i, STYLE_MARKER_CHAR);
+	  assert (res == 3);
+	}
+
+      init = true;
+    }
+
+  /* Return the string that marks switching to STYLE.  */
+  num = (unsigned) style;
+  assert (style <= 0xf);
+  return formats[num];
+}
+
+/* Callback used by aarch64_print_operand to apply STYLE to the
+   disassembler output created from FMT and ARGS.  The STYLER object holds
+   any required state.  Must return a pointer to a string (created from FMT
+   and ARGS) that will continue to be valid until the complete disassembled
+   instruction has been printed.
+
+   We return a string that includes two embedded style markers, the first,
+   places at the start of the string, indicates a switch to STYLE, and the
+   second, placed at the end of the string, indicates a switch back to the
+   default text style.
+
+   Later, when we print the operand text we take care to collapse any
+   adjacent style markers, and to ignore any style markers that appear at
+   the very end of a complete operand string.  */
+
+static const char *aarch64_apply_style (struct aarch64_styler *styler,
+					enum disassembler_style style,
+					const char *fmt,
+					va_list args)
+{
+  int res;
+  char *ptr, *tmp;
+  struct obstack *stack = (struct obstack *) styler->state;
+  va_list ap;
+
+  /* These are the two strings for switching styles.  */
+  const char *style_on = get_style_text (style);
+  const char *style_off = get_style_text (dis_style_text);
+
+  /* Calculate space needed once FMT and ARGS are expanded.  */
+  va_copy (ap, args);
+  res = vsnprintf (NULL, 0, fmt, ap);
+  va_end (ap);
+  assert (res >= 0);
+
+  /* Allocate space on the obstack for the expanded FMT and ARGS, as well
+     as the two strings for switching styles, then write all of these
+     strings onto the obstack.  */
+  ptr = (char *) obstack_alloc (stack, res + strlen (style_on)
+				+ strlen (style_off) + 1);
+  tmp = stpcpy (ptr, style_on);
+  res = vsnprintf (tmp, (res + 1), fmt, args);
+  assert (res >= 0);
+  tmp += res;
+  strcpy (tmp, style_off);
+
+  return ptr;
+}
+
 /* Print operands.  */
 
 static void
@@ -3284,6 +3377,13 @@ print_operands (bfd_vma pc, const aarch64_opcode *opcode,
 {
   char *notes = NULL;
   int i, pcrel_p, num_printed;
+  struct aarch64_styler styler;
+  struct obstack content;
+  obstack_init (&content);
+
+  styler.apply_style = aarch64_apply_style;
+  styler.state = (void *) &content;
+
   for (i = 0, num_printed = 0; i < AARCH64_MAX_OPND_NUM; ++i)
     {
       char str[128];
@@ -3301,33 +3401,97 @@ print_operands (bfd_vma pc, const aarch64_opcode *opcode,
       /* Generate the operand string in STR.  */
       aarch64_print_operand (str, sizeof (str), pc, opcode, opnds, i, &pcrel_p,
 			     &info->target, &notes, cmt, sizeof (cmt),
-			     arch_variant);
+			     arch_variant, &styler);
 
       /* Print the delimiter (taking account of omitted operand(s)).  */
       if (str[0] != '\0')
-	(*info->fprintf_func) (info->stream, "%s",
-			       num_printed++ == 0 ? "\t" : ", ");
+	(*info->fprintf_styled_func) (info->stream, dis_style_text, "%s",
+				      num_printed++ == 0 ? "\t" : ", ");
 
       /* Print the operand.  */
       if (pcrel_p)
 	(*info->print_address_func) (info->target, info);
       else
 	{
-	  (*info->fprintf_func) (info->stream, "%s", str);
-
-	  /* Print the comment.  This works because only the last operand
-	     ever adds a comment.  If that ever changes then we'll need to
-	     be smarter here.  */
-	  if (cmt[0] != '\0')
-	    (*info->fprintf_func) (info->stream, "\t// %s", cmt);
+	  /* This operand came from aarch64_print_operand, and will include
+	     embedded strings indicating which style each character should
+	     have.  In the following code we split the text based on
+	     CURR_STYLE, and call the styled print callback to print each
+	     block of text in the appropriate style.  */
+	  char *start, *curr;
+	  enum disassembler_style curr_style = dis_style_text;
+
+	  start = curr = str;
+	  do
+	    {
+	      if (*curr == '\0'
+		  || (*curr == STYLE_MARKER_CHAR
+		      && ISXDIGIT (*(curr + 1))
+		      && *(curr + 2) == STYLE_MARKER_CHAR))
+		{
+		  /* Output content between our START position and CURR.  */
+		  int len = curr - start;
+		  if (len > 0)
+		    {
+		      if ((*info->fprintf_styled_func) (info->stream,
+							curr_style,
+							"%.*s",
+							len, start) < 0)
+			break;
+		    }
+
+		  if (*curr == '\0')
+		    break;
+
+		  /* Skip over the initial STYLE_MARKER_CHAR.  */
+		  ++curr;
+
+		  /* Update the CURR_STYLE.  As there are less than 16
+		     styles, it is possible, that if the input is corrupted
+		     in some way, that we might set CURR_STYLE to an
+		     invalid value.  Don't worry though, we check for this
+		     situation.  */
+		  if (*curr >= '0' && *curr <= '9')
+		    curr_style = (enum disassembler_style) (*curr - '0');
+		  else if (*curr >= 'a' && *curr <= 'f')
+		    curr_style = (enum disassembler_style) (*curr - 'a' + 10);
+		  else
+		    curr_style = dis_style_text;
+
+		  /* Check for an invalid style having been selected.  This
+		     should never happen, but it doesn't hurt to be a
+		     little paranoid.  */
+		  if (curr_style > dis_style_comment_start)
+		    curr_style = dis_style_text;
+
+		  /* Skip the hex character, and the closing STYLE_MARKER_CHAR.  */
+		  curr += 2;
+
+		  /* Reset the START to after the style marker.  */
+		  start = curr;
+		}
+	      else
+		++curr;
+	    }
+	  while (true);
 	}
+
+      /* Print the comment.  This works because only the last operand ever
+	 adds a comment.  If that ever changes then we'll need to be
+	 smarter here.  */
+      if (cmt[0] != '\0')
+	(*info->fprintf_styled_func) (info->stream, dis_style_comment_start,
+				      "\t// %s", cmt);
     }
 
     if (notes && !no_notes)
       {
 	*has_notes = true;
-	(*info->fprintf_func) (info->stream, "  // note: %s", notes);
+	(*info->fprintf_styled_func) (info->stream, dis_style_comment_start,
+				      "  // note: %s", notes);
       }
+
+    obstack_free (&content, NULL);
 }
 
 /* Set NAME to a copy of INST's mnemonic with the "." suffix removed.  */
@@ -3359,10 +3523,12 @@ print_mnemonic_name (const aarch64_inst *inst, struct disassemble_info *info)
       char name[8];
 
       remove_dot_suffix (name, inst);
-      (*info->fprintf_func) (info->stream, "%s.%s", name, inst->cond->names[0]);
+      (*info->fprintf_styled_func) (info->stream, dis_style_mnemonic,
+				    "%s.%s", name, inst->cond->names[0]);
     }
   else
-    (*info->fprintf_func) (info->stream, "%s", inst->opcode->name);
+    (*info->fprintf_styled_func) (info->stream, dis_style_mnemonic,
+				  "%s", inst->opcode->name);
 }
 
 /* Decide whether we need to print a comment after the operands of
@@ -3379,9 +3545,10 @@ print_comment (const aarch64_inst *inst, struct disassemble_info *info)
       remove_dot_suffix (name, inst);
       num_conds = ARRAY_SIZE (inst->cond->names);
       for (i = 1; i < num_conds && inst->cond->names[i]; ++i)
-	(*info->fprintf_func) (info->stream, "%s %s.%s",
-			       i == 1 ? "  //" : ",",
-			       name, inst->cond->names[i]);
+	(*info->fprintf_styled_func) (info->stream, dis_style_comment_start,
+				      "%s %s.%s",
+				      i == 1 ? "  //" : ",",
+				      name, inst->cond->names[i]);
     }
 }
 
@@ -3398,28 +3565,30 @@ print_verifier_notes (aarch64_operand_error *detail,
      would not have succeeded.  We can safely ignore these.  */
   assert (detail->non_fatal);
 
-  (*info->fprintf_func) (info->stream, "  // note: ");
+  (*info->fprintf_styled_func) (info->stream, dis_style_comment_start,
+				"  // note: ");
   switch (detail->kind)
     {
     case AARCH64_OPDE_A_SHOULD_FOLLOW_B:
-      (*info->fprintf_func) (info->stream,
-			     _("this `%s' should have an immediately"
-			       " preceding `%s'"),
-			     detail->data[0].s, detail->data[1].s);
+      (*info->fprintf_styled_func) (info->stream, dis_style_text,
+				    _("this `%s' should have an immediately"
+				      " preceding `%s'"),
+				    detail->data[0].s, detail->data[1].s);
       break;
 
     case AARCH64_OPDE_EXPECTED_A_AFTER_B:
-      (*info->fprintf_func) (info->stream,
-			     _("expected `%s' after previous `%s'"),
-			     detail->data[0].s, detail->data[1].s);
+      (*info->fprintf_styled_func) (info->stream, dis_style_text,
+				    _("expected `%s' after previous `%s'"),
+				    detail->data[0].s, detail->data[1].s);
       break;
 
     default:
       assert (detail->error);
-      (*info->fprintf_func) (info->stream, "%s", detail->error);
+      (*info->fprintf_styled_func) (info->stream, dis_style_text,
+				    "%s", detail->error);
       if (detail->index >= 0)
-	(*info->fprintf_func) (info->stream, " at operand %d",
-			       detail->index + 1);
+	(*info->fprintf_styled_func) (info->stream, dis_style_text,
+				      " at operand %d", detail->index + 1);
       break;
     }
 }
@@ -3511,8 +3680,13 @@ print_insn_aarch64_word (bfd_vma pc,
     case ERR_NYI:
       /* Handle undefined instructions.  */
       info->insn_type = dis_noninsn;
-      (*info->fprintf_func) (info->stream,".inst\t0x%08x ; %s",
-			     word, err_msg[ret]);
+      (*info->fprintf_styled_func) (info->stream,
+				    dis_style_assembler_directive,
+				    ".inst\t");
+      (*info->fprintf_styled_func) (info->stream, dis_style_immediate,
+				    "0x%08x", word);
+      (*info->fprintf_styled_func) (info->stream, dis_style_comment_start,
+				    " ; %s", err_msg[ret]);
       break;
     case ERR_OK:
       user_friendly_fixup (&inst);
@@ -3554,13 +3728,22 @@ print_insn_data (bfd_vma pc ATTRIBUTE_UNUSED,
   switch (info->bytes_per_chunk)
     {
     case 1:
-      info->fprintf_func (info->stream, ".byte\t0x%02x", word);
+      info->fprintf_styled_func (info->stream, dis_style_assembler_directive,
+				 ".byte\t");
+      info->fprintf_styled_func (info->stream, dis_style_immediate,
+				 "0x%02x", word);
       break;
     case 2:
-      info->fprintf_func (info->stream, ".short\t0x%04x", word);
+      info->fprintf_styled_func (info->stream, dis_style_assembler_directive,
+				 ".short\t");
+      info->fprintf_styled_func (info->stream, dis_style_immediate,
+				 "0x%04x", word);
       break;
     case 4:
-      info->fprintf_func (info->stream, ".word\t0x%08x", word);
+      info->fprintf_styled_func (info->stream, dis_style_assembler_directive,
+				 ".word\t");
+      info->fprintf_styled_func (info->stream, dis_style_immediate,
+				 "0x%08x", word);
       break;
     default:
       abort ();