RISC-V: Emit better warning for unknown CSR.

gas/
	* config/tc-riscv.c (check_absolute_expr): Expand comment.  New
	parameter maybe_csr.  If maybe_csr and O_symbol, print CSR name.
	(riscv_ip): Add new argument to check_absolute_expr calls.
	* testsuite/gas/riscv/bad-csr.d: New.
	* testsuite/gas/riscv/bad-csr.l: New.
	* testsuite/gas/riscv/bad-csr.s: New.

gas/ChangeLog

@@ -1,3 +1,12 @@
+2018-03-16  Jim Wilson  <jimw@sifive.com>
+
+	* config/tc-riscv.c (check_absolute_expr): Expand comment.  New
+	parameter maybe_csr.  If maybe_csr and O_symbol, print CSR name.
+	(riscv_ip): Add new argument to check_absolute_expr calls.
+	* testsuite/gas/riscv/bad-csr.d: New.
+	* testsuite/gas/riscv/bad-csr.l: New.
+	* testsuite/gas/riscv/bad-csr.s: New.
+
 2018-03-14  Kito Cheng  <kito.cheng@gmail.com>
 
 	* config/tc-riscv.c (opcode_name_list): New.

gas/config/tc-riscv.c

@@ -993,13 +993,18 @@ normalize_constant_expr (expressionS *ex)
 			- 0x80000000);
 }
 
-/* Fail if an expression is not a constant.  */
+/* Fail if an expression EX is not a constant.  IP is the instruction using EX.
+   MAYBE_CSR is true if the symbol may be an unrecognized CSR name.  */
 
 static void
-check_absolute_expr (struct riscv_cl_insn *ip, expressionS *ex)
+check_absolute_expr (struct riscv_cl_insn *ip, expressionS *ex,
+		     bfd_boolean maybe_csr)
 {
   if (ex->X_op == O_big)
     as_bad (_("unsupported large constant"));
+  else if (maybe_csr && ex->X_op == O_symbol)
+    as_bad (_("unknown CSR `%s'"),
+	    S_GET_NAME (ex->X_add_symbol));
   else if (ex->X_op != O_constant)
     as_bad (_("Instruction %s requires absolute expression"),
 	    ip->insn_mo->name);
@@ -1744,7 +1749,7 @@ rvc_lui:
 
 	    case '<':		/* Shift amount, 0 - 31.  */
 	      my_getExpression (imm_expr, s);
-	      check_absolute_expr (ip, imm_expr);
+	      check_absolute_expr (ip, imm_expr, FALSE);
 	      if ((unsigned long) imm_expr->X_add_number > 31)
 		as_bad (_("Improper shift amount (%lu)"),
 			(unsigned long) imm_expr->X_add_number);
@@ -1755,7 +1760,7 @@ rvc_lui:
 
 	    case '>':		/* Shift amount, 0 - (XLEN-1).  */
 	      my_getExpression (imm_expr, s);
-	      check_absolute_expr (ip, imm_expr);
+	      check_absolute_expr (ip, imm_expr, FALSE);
 	      if ((unsigned long) imm_expr->X_add_number >= xlen)
 		as_bad (_("Improper shift amount (%lu)"),
 			(unsigned long) imm_expr->X_add_number);
@@ -1766,7 +1771,7 @@ rvc_lui:
 
 	    case 'Z':		/* CSRRxI immediate.  */
 	      my_getExpression (imm_expr, s);
-	      check_absolute_expr (ip, imm_expr);
+	      check_absolute_expr (ip, imm_expr, FALSE);
 	      if ((unsigned long) imm_expr->X_add_number > 31)
 		as_bad (_("Improper CSRxI immediate (%lu)"),
 			(unsigned long) imm_expr->X_add_number);
@@ -1781,7 +1786,7 @@ rvc_lui:
 	      else
 		{
 		  my_getExpression (imm_expr, s);
-		  check_absolute_expr (ip, imm_expr);
+		  check_absolute_expr (ip, imm_expr, TRUE);
 		  if ((unsigned long) imm_expr->X_add_number > 0xfff)
 		    as_bad (_("Improper CSR address (%lu)"),
 			    (unsigned long) imm_expr->X_add_number);

gas/testsuite/gas/riscv/bad-csr.d

@@ -0,0 +1,3 @@
+#as:
+#source: bad-csr.s
+#error-output: bad-csr.l

gas/testsuite/gas/riscv/bad-csr.l

@@ -0,0 +1,2 @@
+.*: Assembler messages:
+.*: Error: unknown CSR `nonexistent'

gas/testsuite/gas/riscv/bad-csr.s

@@ -0,0 +1 @@
+	csrr a0, nonexistent