target/riscv: Expose "priv" register for GDB for reads

This patch enables a debugger to read the current privilege level via a virtual
"priv" register. When compiled with CONFIG_USER_ONLY the register is still
visible but always reports the value zero.

Signed-off-by: Jonathan Behrens <jonathan@fintelia.io>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/target/riscv/gdbstub.c b/target/riscv/gdbstub.c
index cb5bfd3..1f71604 100644
--- a/target/riscv/gdbstub.c
+++ b/target/riscv/gdbstub.c
@@ -373,6 +373,23 @@ static int riscv_gdb_set_csr(CPURISCVState *env, uint8_t *mem_buf, int n)
     return 0;
 }
 
+static int riscv_gdb_get_virtual(CPURISCVState *cs, uint8_t *mem_buf, int n)
+{
+    if (n == 0) {
+#ifdef CONFIG_USER_ONLY
+        return gdb_get_regl(mem_buf, 0);
+#else
+        return gdb_get_regl(mem_buf, cs->priv);
+#endif
+    }
+    return 0;
+}
+
+static int riscv_gdb_set_virtual(CPURISCVState *cs, uint8_t *mem_buf, int n)
+{
+    return 0;
+}
+
 void riscv_cpu_register_gdb_regs_for_features(CPUState *cs)
 {
     RISCVCPU *cpu = RISCV_CPU(cs);
@@ -385,6 +402,9 @@ void riscv_cpu_register_gdb_regs_for_features(CPUState *cs)
 
     gdb_register_coprocessor(cs, riscv_gdb_get_csr, riscv_gdb_set_csr,
                              240, "riscv-32bit-csr.xml", 0);
+
+    gdb_register_coprocessor(cs, riscv_gdb_get_virtual, riscv_gdb_set_virtual,
+                             1, "riscv-32bit-virtual.xml", 0);
 #elif defined(TARGET_RISCV64)
     if (env->misa & RVF) {
         gdb_register_coprocessor(cs, riscv_gdb_get_fpu, riscv_gdb_set_fpu,
@@ -393,5 +413,8 @@ void riscv_cpu_register_gdb_regs_for_features(CPUState *cs)
 
     gdb_register_coprocessor(cs, riscv_gdb_get_csr, riscv_gdb_set_csr,
                              240, "riscv-64bit-csr.xml", 0);
+
+    gdb_register_coprocessor(cs, riscv_gdb_get_virtual, riscv_gdb_set_virtual,
+                             1, "riscv-64bit-virtual.xml", 0);
 #endif
 }