[PATCH 1/6] target/riscv: add check for supported privilege modes conbinations

[Weiwei Li]

- There are 3 suggested privilege modes conbinations listed in the spec:
1) M, 2) M, U 3) M, S, U

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
---
 target/riscv/cpu.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 1bb3973806..0dad6906bc 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -636,6 +636,12 @@ static void riscv_cpu_realize(DeviceState *dev, Error 
**errp)
             return;
         }
 
+        if (cpu->cfg.ext_s && !cpu->cfg.ext_u) {
+            error_setg(errp,
+                       "Setting S extension without U extension is illegal");
+            return;
+        }
+
         if (cpu->cfg.ext_f && !cpu->cfg.ext_icsr) {
             error_setg(errp, "F extension requires Zicsr");
             return;
-- 
2.17.1