RISC-V: Error for relaxable branch in absolute section.

Emit an error instead of crashing in frag_new, handling this same as the
i386 port.

gas/
	PR 26400
	* config/tc-riscv.c (append_insn): If in absolute section, emit
	error before add_relaxed_insn call.
	* testsuite/gas/riscv/absolute-sec.d: New.
	* testsuite/gas/riscv/absolute-sec.l: New.
	* testsuite/gas/riscv/absolute-sec.s: New.

gas/ChangeLog

@@ -1,3 +1,12 @@
+2020-09-24  Jim Wilson  <jimw@sifive.com>
+
+	PR 26400
+	* config/tc-riscv.c (append_insn): If in absolute section, emit
+	error before add_relaxed_insn call.
+	* testsuite/gas/riscv/absolute-sec.d: New.
+	* testsuite/gas/riscv/absolute-sec.l: New.
+	* testsuite/gas/riscv/absolute-sec.s: New.
+
 2020-09-23  Mark Wielaard  <mark@klomp.org>
 
 	* testsuite/gas/elf/dwarf-5-cu.d: Adjust expected output.

gas/config/tc-riscv.c

@@ -1106,6 +1106,13 @@ append_insn (struct riscv_cl_insn *ip, expressionS *address_expr,
 	  int j = reloc_type == BFD_RELOC_RISCV_JMP;
 	  int best_case = riscv_insn_length (ip->insn_opcode);
 	  unsigned worst_case = relaxed_branch_length (NULL, NULL, 0);
+
+	  if (now_seg == absolute_section)
+	    {
+	      as_bad (_("relaxable branches not supported in absolute section"));
+	      return;
+	    }
+
 	  add_relaxed_insn (ip, worst_case, best_case,
 			    RELAX_BRANCH_ENCODE (j, best_case == 2, worst_case),
 			    address_expr->X_add_symbol,

gas/testsuite/gas/riscv/absolute-sec.d

@@ -0,0 +1,3 @@
+#as:
+#source absolute-sec.s
+#error_output: absolute-sec.l

gas/testsuite/gas/riscv/absolute-sec.l

@@ -0,0 +1,2 @@
+.*: Assembler messages:
+.*: Error: relaxable branches not supported in absolute section

gas/testsuite/gas/riscv/absolute-sec.s

@@ -0,0 +1,2 @@
+	.offset 0
+	jal x0, 100