[RFC 15/15] target/riscv: rvb: support and turn on B-extension from command line

[frank . chang]

From: Kito Cheng <kito.cheng@sifive.com>

B-extension is default off, use cpu rv32 or rv64 with x-b=true to
enable B-extension.

Signed-off-by: Kito Cheng <kito.cheng@sifive.com>
---
 target/riscv/cpu.c | 4 ++++
 target/riscv/cpu.h | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 0bbfd7f4574..bc29e118c6d 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -438,6 +438,9 @@ static void riscv_cpu_realize(DeviceState *dev, Error 
**errp)
         if (cpu->cfg.ext_h) {
             target_misa |= RVH;
         }
+        if (cpu->cfg.ext_b) {
+            target_misa |= RVB;
+        }
         if (cpu->cfg.ext_v) {
             target_misa |= RVV;
             if (!is_power_of_2(cpu->cfg.vlen)) {
@@ -515,6 +518,7 @@ static Property riscv_cpu_properties[] = {
     DEFINE_PROP_BOOL("s", RISCVCPU, cfg.ext_s, true),
     DEFINE_PROP_BOOL("u", RISCVCPU, cfg.ext_u, true),
     /* This is experimental so mark with 'x-' */
+    DEFINE_PROP_BOOL("x-b", RISCVCPU, cfg.ext_b, true),
     DEFINE_PROP_BOOL("x-h", RISCVCPU, cfg.ext_h, false),
     DEFINE_PROP_BOOL("x-v", RISCVCPU, cfg.ext_v, false),
     DEFINE_PROP_BOOL("Counters", RISCVCPU, cfg.ext_counters, true),
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index de4705bb578..c1c77c58a87 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -66,6 +66,7 @@
 #define RVS RV('S')
 #define RVU RV('U')
 #define RVH RV('H')
+#define RVB RV('B')
 
 /* S extension denotes that Supervisor mode exists, however it is possible
    to have a core that support S mode but does not have an MMU and there
@@ -278,6 +279,7 @@ struct RISCVCPU {
         bool ext_f;
         bool ext_d;
         bool ext_c;
+        bool ext_b;
         bool ext_s;
         bool ext_u;
         bool ext_h;
-- 
2.17.1