gas/expr.c: 0b vs 0b0 vs 00b

[Alan Modra]

On Fri, Aug 07, 2015 at 01:39:34AM -0400, DJ Delorie wrote:
> 
> For targets with both NUMBERS_WITH_SUFFIX and LOCAL_LABELS_FB, there
> is a parse ambiquity between various binary constants:
> 
> 0b	backward reference
> 1b	binary value, suffix
> 0b1	binary value, prefix

Actually 1b is a backward reference too.  I think both 0b and 1b
without following binary digits ought to be treated as backward refs
on these targets, since if you want to write a binary 0 or 1 with an
explicit suffix that can be done as 0B or 1B.

> The third will be parsed as 0b followed by "junk".  This patch checks
> for 0b followed by further binary digits and bypasses the b-as-suffix
> rule.
> 
> I don't think a generic test case would work, since it would have to
> test expressions that are only valid on some targets.  Would one
> target's test suffice, or should the test be duplicated across many
> targets?

I think a single target test is sufficient.  I've been playing with
variants of the following.

 .text
_start:
 .byte 0f - _start
 .byte 1f - _start
0:
 .byte 0b - _start
1:
 .byte 1b - _start
 .byte 0b0, 0b1, 0B0, 0B1
 .byte 0B, 1B

Here's a patch that extends yours a little.  What do you think?

    	* expr.c (integer_constant): Return O_absent expression if eol.
    	(operand): For targets with both LOCAL_LABELS_FB and
    	NUMBERS_WITH_SUFFIX set, treat "0b" not followed by binary
    	digits as a local label reference.  Correct handling of 0b prefix.
	If a suffix is not allowed, error on 0B.

diff --git a/gas/expr.c b/gas/expr.c
index 106f06d..2dae6ba 100644
--- a/gas/expr.c
+++ b/gas/expr.c
@@ -285,6 +285,12 @@ integer_constant (int radix, expressionS *expressionP)
 #define valuesize 32
 #endif
 
+  if (is_end_of_line[(unsigned char) *input_line_pointer])
+    {
+      expressionP->X_op = O_absent;
+      return;
+    }
+
   if ((NUMBERS_WITH_SUFFIX || flag_m68k_mri) && radix == 0)
     {
       int flt = 0;
@@ -832,32 +838,28 @@ operand (expressionS *expressionP, enum expr_mode mode)
 	  break;
 
 	case 'b':
-	  if (LOCAL_LABELS_FB && ! (flag_m68k_mri || NUMBERS_WITH_SUFFIX))
+	  if (LOCAL_LABELS_FB && !flag_m68k_mri
+	      && input_line_pointer[1] != '0'
+	      && input_line_pointer[1] != '1')
 	    {
-	      /* This code used to check for '+' and '-' here, and, in
-		 some conditions, fall through to call
-		 integer_constant.  However, that didn't make sense,
-		 as integer_constant only accepts digits.  */
-	      /* Some of our code elsewhere does permit digits greater
-		 than the expected base; for consistency, do the same
-		 here.  */
-	      if (input_line_pointer[1] < '0'
-		  || input_line_pointer[1] > '9')
-		{
-		  /* Parse this as a back reference to label 0.  */
-		  input_line_pointer--;
-		  integer_constant (10, expressionP);
-		  break;
-		}
-	      /* Otherwise, parse this as a binary number.  */
+	      /* Parse this as a back reference to label 0.  */
+	      input_line_pointer--;
+	      integer_constant (10, expressionP);
+	      break;
 	    }
+	  /* Otherwise, parse this as a binary number.  */
 	  /* Fall through.  */
 	case 'B':
-	  input_line_pointer++;
+	  if (input_line_pointer[1] == '0'
+	      || input_line_pointer[1] == '1')
+	    {
+	      input_line_pointer++;
+	      integer_constant (2, expressionP);
+	      break;
+	    }
 	  if (flag_m68k_mri || NUMBERS_WITH_SUFFIX)
-	    goto default_case;
-	  integer_constant (2, expressionP);
-	  break;
+	    input_line_pointer++;
+	  goto default_case;
 
 	case '0':
 	case '1':

-- 
Alan Modra
Australia Development Lab, IBM