Allow non-fatal errors to be emitted and for disassembly notes be placed on AArch64

This patch adds a new platform option "notes" that can be used to indicate if
disassembly notes should be placed in the disassembly as comments.

These notes can contain information about a failing constraint such as reading
from a write-only register.  The disassembly will not be blocked because of this
but -M notes will emit a comment saying that the operation is not allowed.

For assembly this patch adds a new non-fatal status for errors.  This is
essentially a warning.  The reason for not creating an actual warning type is
that this causes the interaction between the ordering of warnings and errors to
be problematic.  Currently the error buffer is almost always filled because of
the way operands are matched during assembly. An earlier template may have put
an error there that would only be displayed if no other template matches or
generates a higher priority error.  But by definition a warning is lower
priority than a warning, so the error (which is incorrect if another template
matched) will supersede the warning.  By treating warnings as errors and only
later relaxing the severity this relationship keeps working and the existing
reporting infrastructure can be re-used.

binutils/

	PR binutils/21446
	* doc/binutils.texi (-M): Document AArch64 options.
	* NEWS: Document notes and warnings.

gas/

	PR binutils/21446
	* config/tc-aarch64.c (print_operands): Indicate no notes.
	(output_operand_error_record): Support non-fatal errors.
	(output_operand_error_report, warn_unpredictable_ldst, md_assemble):
	Likewise.

include/

	PR binutils/21446
	* opcode/aarch64.h (aarch64_operand_error): Add non_fatal.
	(aarch64_print_operand): Support notes.

opcodes/

	PR binutils/21446
	* aarch64-dis.c (no_notes: New.
	(parse_aarch64_dis_option): Support notes.
	(aarch64_decode_insn, print_operands): Likewise.
	(print_aarch64_disassembler_options): Document notes.
	* aarch64-opc.c (aarch64_print_operand): Support notes.

2 files changed, 89 insertions, 51 deletions

diff --git a/gas/ChangeLog b/gas/ChangeLog
index 60a00f0..84bba4b 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,6 +1,14 @@
 2018-05-15  Tamar Christina  <tamar.christina@arm.com>
 
 	PR binutils/21446
+	* config/tc-aarch64.c (print_operands): Indicate no notes.
+	(output_operand_error_record): Support non-fatal errors.
+	(output_operand_error_report, warn_unpredictable_ldst, md_assemble):
+	Likewise.
+
+2018-05-15  Tamar Christina  <tamar.christina@arm.com>
+
+	PR binutils/21446
 	* config/tc-aarch64.c (parse_sys_reg): Return register flags.
 	(parse_operands): Fill in register flags.
 
diff --git a/gas/config/tc-aarch64.c b/gas/config/tc-aarch64.c
index 750025a..b007fb3 100644
--- a/gas/config/tc-aarch64.c
+++ b/gas/config/tc-aarch64.c
@@ -4533,7 +4533,8 @@ print_operands (char *buf, const aarch64_opcode *opcode,
 	break;
 
       /* Generate the operand string in STR.  */
-      aarch64_print_operand (str, sizeof (str), 0, opcode, opnds, i, NULL, NULL);
+      aarch64_print_operand (str, sizeof (str), 0, opcode, opnds, i, NULL, NULL,
+			     NULL);
 
       /* Delimiter.  */
       if (str[0] != '\0')
@@ -4579,12 +4580,14 @@ output_operand_error_record (const operand_error_record *record, char *str)
   enum aarch64_opnd opd_code = (idx >= 0 ? opcode->operands[idx]
 				: AARCH64_OPND_NIL);
 
+  typedef void (*handler_t)(const char *format, ...);
+  handler_t handler = detail->non_fatal ? as_warn : as_bad;
+
   switch (detail->kind)
     {
     case AARCH64_OPDE_NIL:
       gas_assert (0);
       break;
-
     case AARCH64_OPDE_SYNTAX_ERROR:
     case AARCH64_OPDE_RECOVERABLE:
     case AARCH64_OPDE_FATAL_SYNTAX_ERROR:
@@ -4594,21 +4597,21 @@ output_operand_error_record (const operand_error_record *record, char *str)
       if (detail->error != NULL)
 	{
 	  if (idx < 0)
-	    as_bad (_("%s -- `%s'"), detail->error, str);
+	    handler (_("%s -- `%s'"), detail->error, str);
 	  else
-	    as_bad (_("%s at operand %d -- `%s'"),
-		    detail->error, idx + 1, str);
+	    handler (_("%s at operand %d -- `%s'"),
+		     detail->error, idx + 1, str);
 	}
       else
 	{
 	  gas_assert (idx >= 0);
-	  as_bad (_("operand %d must be %s -- `%s'"), idx + 1,
-		aarch64_get_operand_desc (opd_code), str);
+	  handler (_("operand %d must be %s -- `%s'"), idx + 1,
+		   aarch64_get_operand_desc (opd_code), str);
 	}
       break;
 
     case AARCH64_OPDE_INVALID_VARIANT:
-      as_bad (_("operand mismatch -- `%s'"), str);
+      handler (_("operand mismatch -- `%s'"), str);
       if (verbose_error_p)
 	{
 	  /* We will try to correct the erroneous instruction and also provide
@@ -4705,36 +4708,36 @@ output_operand_error_record (const operand_error_record *record, char *str)
       break;
 
     case AARCH64_OPDE_UNTIED_OPERAND:
-      as_bad (_("operand %d must be the same register as operand 1 -- `%s'"),
-	      detail->index + 1, str);
+      handler (_("operand %d must be the same register as operand 1 -- `%s'"),
+	       detail->index + 1, str);
       break;
 
     case AARCH64_OPDE_OUT_OF_RANGE:
       if (detail->data[0] != detail->data[1])
-	as_bad (_("%s out of range %d to %d at operand %d -- `%s'"),
-		detail->error ? detail->error : _("immediate value"),
-		detail->data[0], detail->data[1], idx + 1, str);
+	handler (_("%s out of range %d to %d at operand %d -- `%s'"),
+		 detail->error ? detail->error : _("immediate value"),
+		 detail->data[0], detail->data[1], idx + 1, str);
       else
-	as_bad (_("%s must be %d at operand %d -- `%s'"),
-		detail->error ? detail->error : _("immediate value"),
-		detail->data[0], idx + 1, str);
+	handler (_("%s must be %d at operand %d -- `%s'"),
+		 detail->error ? detail->error : _("immediate value"),
+		 detail->data[0], idx + 1, str);
       break;
 
     case AARCH64_OPDE_REG_LIST:
       if (detail->data[0] == 1)
-	as_bad (_("invalid number of registers in the list; "
-		  "only 1 register is expected at operand %d -- `%s'"),
-		idx + 1, str);
+	handler (_("invalid number of registers in the list; "
+		   "only 1 register is expected at operand %d -- `%s'"),
+		 idx + 1, str);
       else
-	as_bad (_("invalid number of registers in the list; "
-		  "%d registers are expected at operand %d -- `%s'"),
-	      detail->data[0], idx + 1, str);
+	handler (_("invalid number of registers in the list; "
+		   "%d registers are expected at operand %d -- `%s'"),
+	       detail->data[0], idx + 1, str);
       break;
 
     case AARCH64_OPDE_UNALIGNED:
-      as_bad (_("immediate value must be a multiple of "
-		"%d at operand %d -- `%s'"),
-	      detail->data[0], idx + 1, str);
+      handler (_("immediate value must be a multiple of "
+		 "%d at operand %d -- `%s'"),
+	       detail->data[0], idx + 1, str);
       break;
 
     default:
@@ -4748,10 +4751,15 @@ output_operand_error_record (const operand_error_record *record, char *str)
    When this function is called, the operand error information had
    been collected for an assembly line and there will be multiple
    errors in the case of multiple instruction templates; output the
-   error message that most closely describes the problem.  */
+   error message that most closely describes the problem.
+
+   The errors to be printed can be filtered on printing all errors
+   or only non-fatal errors.  This distinction has to be made because
+   the error buffer may already be filled with fatal errors we don't want to
+   print due to the different instruction templates.  */
 
 static void
-output_operand_error_report (char *str)
+output_operand_error_report (char *str, bfd_boolean non_fatal_only)
 {
   int largest_error_pos;
   const char *msg = NULL;
@@ -4769,9 +4777,14 @@ output_operand_error_report (char *str)
   /* Only one error.  */
   if (head == operand_error_report.tail)
     {
-      DEBUG_TRACE ("single opcode entry with error kind: %s",
-		   operand_mismatch_kind_names[head->detail.kind]);
-      output_operand_error_record (head, str);
+      /* If the only error is a non-fatal one and we don't want to print it,
+	 just exit.  */
+      if (!non_fatal_only || head->detail.non_fatal)
+	{
+	  DEBUG_TRACE ("single opcode entry with error kind: %s",
+		       operand_mismatch_kind_names[head->detail.kind]);
+	  output_operand_error_record (head, str);
+	}
       return;
     }
 
@@ -4791,7 +4804,10 @@ output_operand_error_report (char *str)
   largest_error_pos = -2; /* Index can be -1 which means unknown index.  */
   for (curr = head; curr != NULL; curr = curr->next)
     {
-      if (curr->detail.kind != kind)
+      /* If we don't want to print non-fatal errors then don't consider them
+	 at all.  */
+      if (curr->detail.kind != kind
+	  || (non_fatal_only && !head->detail.non_fatal))
 	continue;
       /* If there are multiple errors, pick up the one with the highest
 	 mismatching operand index.  In the case of multiple errors with
@@ -4807,6 +4823,17 @@ output_operand_error_report (char *str)
 	}
     }
 
+  /* The way errors are collected in the back-end is a bit non-intuitive.  But
+     essentially, because each operand template is tried recursively you may
+     always have errors collected from the previous tried OPND.  These are
+     usually skipped if there is one successful match.  However now with the
+     non-fatal errors we have to ignore those previously collected hard errors
+     when we're only interested in printing the non-fatal ones.  This condition
+     prevents us from printing errors that are not appropriate, since we did
+     match a condition, but it also has warnings that it wants to print.  */
+  if (non_fatal_only && !record)
+    return;
+
   gas_assert (largest_error_pos != -2 && record != NULL);
   DEBUG_TRACE ("Pick up error kind %s to report",
 	       operand_mismatch_kind_names[record->detail.kind]);
@@ -6352,18 +6379,18 @@ parse_operands (char *str, const aarch64_opcode *opcode)
 	  goto regoff_addr;
 
 	case AARCH64_OPND_SYSREG:
-	 {
-	   uint32_t sysreg_flags;
-	   if ((val = parse_sys_reg (&str, aarch64_sys_regs_hsh, 1, 0,
-				     &sysreg_flags)) == PARSE_FAIL)
-	     {
-	       set_syntax_error (_("unknown or missing system register name"));
-	       goto failure;
-	     }
-	   inst.base.operands[i].sysreg.value = val;
-	   inst.base.operands[i].sysreg.flags = sysreg_flags;
-	   break;
-	 }
+	  {
+	    uint32_t sysreg_flags;
+	    if ((val = parse_sys_reg (&str, aarch64_sys_regs_hsh, 1, 0,
+				      &sysreg_flags)) == PARSE_FAIL)
+	      {
+		set_syntax_error (_("unknown or missing system register name"));
+		goto failure;
+	      }
+	    inst.base.operands[i].sysreg.value = val;
+	    inst.base.operands[i].sysreg.flags = sysreg_flags;
+	    break;
+	  }
 
 	case AARCH64_OPND_PSTATEFIELD:
 	  if ((val = parse_sys_reg (&str, aarch64_pstatefield_hsh, 0, 1, NULL))
@@ -6689,15 +6716,15 @@ do_encode (const aarch64_opcode *opcode, aarch64_inst *instr,
 	   aarch64_insn *code)
 {
   aarch64_operand_error error_info;
+  memset (&error_info, '\0', sizeof (error_info));
   error_info.kind = AARCH64_OPDE_NIL;
-  if (aarch64_opcode_encode (opcode, instr, code, NULL, &error_info))
+  if (aarch64_opcode_encode (opcode, instr, code, NULL, &error_info)
+      && !error_info.non_fatal)
     return TRUE;
-  else
-    {
-      gas_assert (error_info.kind != AARCH64_OPDE_NIL);
-      record_operand_error_info (opcode, &error_info);
-      return FALSE;
-    }
+
+  gas_assert (error_info.kind != AARCH64_OPDE_NIL);
+  record_operand_error_info (opcode, &error_info);
+  return error_info.non_fatal;
 }
 
 #ifdef DEBUG_AARCH64
@@ -6834,6 +6861,9 @@ md_assemble (char *str)
 	      memcpy (copy, &inst.base, sizeof (struct aarch64_inst));
 	      output_inst (copy);
 	    }
+
+	  /* Issue non-fatal messages if any.  */
+	  output_operand_error_report (str, TRUE);
 	  return;
 	}
 
@@ -6847,7 +6877,7 @@ md_assemble (char *str)
   while (template != NULL);
 
   /* Issue the error messages if any.  */
-  output_operand_error_report (str);
+  output_operand_error_report (str, FALSE);
 }
 
 /* Various frobbings of labels and their addresses.  */