RISC-V: Don't segfault for two regs in auipc or lui.

gas/
	PR gas/23954
	* config/tc-riscv.c (my_getSmallExpression): Expand comment for
	register support.  Set expr_end if parse a register.
	(riscv_ip) <'u'>: Break if imm_expr is not a symbol or constant.
	* testsuite/gas/riscv/auipc-parsing.d: New.
	* testsuite/gas/riscv/auipc-parsing.l: New.
	* testsuite/gas/riscv/auipc-parsing.s: New.

gas/ChangeLog

@@ -1,3 +1,13 @@
+2018-12-10  Jim Wilson  <jimw@sifive.com>
+
+	PR gas/23954
+	* config/tc-riscv.c (my_getSmallExpression): Expand comment for
+	register support.  Set expr_end if parse a register.
+	(riscv_ip) <'u'>: Break if imm_expr is not a symbol or constant.
+	* testsuite/gas/riscv/auipc-parsing.d: New.
+	* testsuite/gas/riscv/auipc-parsing.l: New.
+	* testsuite/gas/riscv/auipc-parsing.s: New.
+
 2018-12-09  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR gas/23968

gas/config/tc-riscv.c

@@ -1263,11 +1263,15 @@ my_getSmallExpression (expressionS *ep, bfd_reloc_code_real_type *reloc,
   unsigned crux_depth, str_depth, regno;
   char *crux;
 
-  /* First, check for integer registers.  */
+  /* First, check for integer registers.  No callers can accept a reg, but
+     we need to avoid accidentally creating a useless undefined symbol below,
+     if this is an instruction pattern that can't match.  A glibc build fails
+     if this is removed.  */
   if (reg_lookup (&str, RCLASS_GPR, &regno))
     {
       ep->X_op = O_register;
       ep->X_add_number = regno;
+      expr_end = str;
       return 0;
     }
 
@@ -1940,6 +1944,9 @@ branch:
 		  *imm_reloc = BFD_RELOC_RISCV_HI20;
 		  imm_expr->X_add_number <<= RISCV_IMM_BITS;
 		}
+	      /* The 'u' format specifier must be a symbol or a constant.  */
+	      if (imm_expr->X_op != O_symbol && imm_expr->X_op != O_constant)
+	        break;
 	      s = expr_end;
 	      continue;
 

gas/testsuite/gas/riscv/auipc-parsing.d

@@ -0,0 +1,3 @@
+#as:
+#source: auipc-parsing.s
+#error_output: auipc-parsing.l

gas/testsuite/gas/riscv/auipc-parsing.l

@@ -0,0 +1,3 @@
+.*: Assembler messages:
+.*: Error: illegal operands `auipc x8,x9'
+.*: Error: illegal operands `lui x10,x11'

gas/testsuite/gas/riscv/auipc-parsing.s

@@ -0,0 +1,3 @@
+# Don't accept a register for 'u' operands.
+	auipc	x8,x9
+	lui	x10,x11