gdb: riscv: Add target description

Target description is not currently implemented in RISC-V
architecture. Thus GDB won't set it properly when attached.
The patch implements the target description response.

Signed-off-by: Sylvain Pelissier <sylvain.pelissier@gmail.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20210106204141.14027-1-sylvain.pelissier@gmail.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.c

@@ -557,6 +557,18 @@ static Property riscv_cpu_properties[] = {
     DEFINE_PROP_END_OF_LIST(),
 };
 
+static gchar *riscv_gdb_arch_name(CPUState *cs)
+{
+    RISCVCPU *cpu = RISCV_CPU(cs);
+    CPURISCVState *env = &cpu->env;
+
+    if (riscv_cpu_is_32bit(env)) {
+        return g_strdup("riscv:rv32");
+    } else {
+        return g_strdup("riscv:rv64");
+    }
+}
+
 static void riscv_cpu_class_init(ObjectClass *c, void *data)
 {
     RISCVCPUClass *mcc = RISCV_CPU_CLASS(c);
@@ -592,6 +604,7 @@ static void riscv_cpu_class_init(ObjectClass *c, void *data)
     /* For now, mark unmigratable: */
     cc->vmsd = &vmstate_riscv_cpu;
 #endif
+    cc->gdb_arch_name = riscv_gdb_arch_name;
 #ifdef CONFIG_TCG
     cc->tcg_initialize = riscv_translate_init;
     cc->tlb_fill = riscv_cpu_tlb_fill;