[PATCH] x86/gas: replace inappropriate assertion when parsing registers

[Jan Beulich]

PR gas/30117
Once a symbol had its expression evaluated, the "segment" of the symbol
may be reg_section if a register is merely involved in the expression,
not just when the expression references a "plain" register. Therefore
the first of the assertions put in place by 4d1bb7955a8b was too strict.
Convert it to an if() to deal with situations like this one found by
fuzzing:

	x=s
	s=%eax+0
	y=s
	or $6,x

In non-debug builds this also avoids potentially silently generating bad
code.

--- a/gas/config/tc-i386.c
+++ b/gas/config/tc-i386.c
@@ -13057,17 +13057,19 @@ parse_register (char *reg_string, char *
 	{
 	  const expressionS *e = symbol_get_value_expression (symbolP);
 
-	  know (e->X_op == O_register);
-	  know (e->X_add_number >= 0
-		&& (valueT) e->X_add_number < i386_regtab_size);
-	  r = i386_regtab + e->X_add_number;
-	  if (!check_register (r))
+	  if (e->X_op == O_register)
+	    {
+	      know (e->X_add_number >= 0
+		    && (valueT) e->X_add_number < i386_regtab_size);
+	      r = i386_regtab + e->X_add_number;
+	      *end_op = input_line_pointer;
+	    }
+	  if (r && !check_register (r))
 	    {
 	      as_bad (_("register '%s%s' cannot be used here"),
 		      register_prefix, r->reg_name);
 	      r = &bad_reg;
 	    }
-	  *end_op = input_line_pointer;
 	}
       *input_line_pointer = c;
       input_line_pointer = save;