RISC-V: Print top GP-relative addresses on the disassembler

This patch makes possible to print the address relative to the global
pointer even if the corresponding symbol is the highest address (0xffffffff
on RV32, 0xffffffff_ffffffff on RV64).

Despite that it is very rare to have GP the highest address, it would be
nice because we enabled highest address printing on regular cases.

opcodes/ChangeLog:

	* riscv-dis.c (struct riscv_private_data): Add `has_gp' to enable
	printing the addresses relative to GP with the highest address.
	(maybe_print_address): Utilize `has_gp'.
	(riscv_disassemble_insn): Likewise.

gas/ChangeLog:

	* testsuite/gas/riscv/dis-addr-topaddr-gp.s: New test for GP-
	relative addressing when GP is the highest address.
	* testsuite/gas/riscv/dis-addr-topaddr-gp-32.d: Likewise.
	* testsuite/gas/riscv/dis-addr-topaddr-gp-64.d: Likewise.

gas/testsuite/gas/riscv/dis-addr-topaddr-gp-32.d

@@ -0,0 +1,12 @@
+#as: -march=rv32i
+#source: dis-addr-topaddr-gp.s
+#objdump: -d
+
+.*:     file format elf32-(little|big)riscv
+
+
+Disassembly of section .text:
+
+0+000 <target>:
+[ 	]+[0-9a-f]+:[ 	]+0051a283[ 	]+lw[   	]+t0,5\(gp\) # 4 <addr_rel_gp_pos>
+[ 	]+[0-9a-f]+:[ 	]+ffd1a303[ 	]+lw[   	]+t1,-3\(gp\) # fffffffc <addr_rel_gp_neg>

gas/testsuite/gas/riscv/dis-addr-topaddr-gp-64.d

@@ -0,0 +1,12 @@
+#as: -march=rv64i -defsym rv64=1
+#source: dis-addr-topaddr-gp.s
+#objdump: -d
+
+.*:     file format elf64-(little|big)riscv
+
+
+Disassembly of section .text:
+
+0+000 <target>:
+[ 	]+[0-9a-f]+:[ 	]+0051a283[ 	]+lw[   	]+t0,5\(gp\) # 4 <addr_rel_gp_pos>
+[ 	]+[0-9a-f]+:[ 	]+ffd1a303[ 	]+lw[   	]+t1,-3\(gp\) # fffffffffffffffc <addr_rel_gp_neg>

gas/testsuite/gas/riscv/dis-addr-topaddr-gp.s

@@ -0,0 +1,15 @@
+.ifdef rv64
+topbase = 0xffffffff00000000
+.else
+topbase = 0
+.endif
+
+.set __global_pointer$, topbase + 0xffffffff  # -1
+.set addr_rel_gp_pos,             0x00000004  # +4
+.set addr_rel_gp_neg,   topbase + 0xfffffffc  # -4
+
+target:
+	# Use addresses relative to gp
+	# (gp is the highest address)
+	lw	t0, +5(gp)
+	lw	t1, -3(gp)

opcodes/riscv-dis.c

@@ -53,6 +53,7 @@ struct riscv_private_data
   bfd_vma print_addr;
   bfd_vma hi_addr[OP_MASK_RD + 1];
   bool to_print_addr;
+  bool has_gp;
 };
 
 /* Used for mapping symbols.  */
@@ -178,7 +179,7 @@ maybe_print_address (struct riscv_private_data *pd, int base_reg, int offset,
       pd->print_addr = (base_reg != 0 ? pd->hi_addr[base_reg] : 0) + offset;
       pd->hi_addr[base_reg] = -1;
     }
-  else if (base_reg == X_GP && pd->gp != (bfd_vma)-1)
+  else if (base_reg == X_GP && pd->has_gp)
     pd->print_addr = pd->gp + offset;
   else if (base_reg == X_TP || base_reg == 0)
     pd->print_addr = offset;
@@ -603,15 +604,19 @@ riscv_disassemble_insn (bfd_vma memaddr, insn_t word, disassemble_info *info)
       int i;
 
       pd = info->private_data = xcalloc (1, sizeof (struct riscv_private_data));
-      pd->gp = -1;
+      pd->gp = 0;
       pd->print_addr = 0;
       for (i = 0; i < (int)ARRAY_SIZE (pd->hi_addr); i++)
 	pd->hi_addr[i] = -1;
       pd->to_print_addr = false;
+      pd->has_gp = false;
 
       for (i = 0; i < info->symtab_size; i++)
 	if (strcmp (bfd_asymbol_name (info->symtab[i]), RISCV_GP_SYMBOL) == 0)
-	  pd->gp = bfd_asymbol_value (info->symtab[i]);
+	  {
+	    pd->gp = bfd_asymbol_value (info->symtab[i]);
+	    pd->has_gp = true;
+	  }
     }
   else
     pd = info->private_data;