The stval register can optionally contain the faulting instruction
on an illegal instruction exception. This patch adds support for setting
the stval register based on the CPU feature.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
---
 target/riscv/cpu.h    |  3 ++-
 target/riscv/helper.c | 13 +++++++++++--
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 1bc46aa952..b797850816 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -86,7 +86,8 @@
    so a cpu features bitfield is required */
 enum {
     RISCV_FEATURE_MMU,
-    RISCV_FEATURE_MTVAL_INST
+    RISCV_FEATURE_MTVAL_INST,
+    RISCV_FEATURE_STVAL_INST
 };
 
 #define USER_VERSION_2_02_0 0x00020200
diff --git a/target/riscv/helper.c b/target/riscv/helper.c
index bd78bcff28..924a49d06f 100644
--- a/target/riscv/helper.c
+++ b/target/riscv/helper.c
@@ -466,9 +466,18 @@ void riscv_cpu_do_interrupt(CPUState *cs)
                     ": badaddr 0x" TARGET_FMT_lx, env->mhartid, env->badaddr);
             }
             env->stval = env->badaddr;
+        } else if (cs->exception_index & RISCV_EXCP_ILLEGAL_INST) {
+            if (riscv_feature(env, RISCV_FEATURE_STVAL_INST)) {
+                /* The stval register can optionally also be used to
+                 * return the faulting instruction bits on an illegal
+                 * instruction exception.
+                 */
+                env->stval = env->bins;
+            } else {
+                env->stval = 0;
+            }
         } else {
-            /* otherwise we must clear sbadaddr/stval
-             * todo: support populating stval on illegal instructions */
+            /* Otherwise we must clear mbadaddr/stval */
             env->stval = 0;
         }
 
-- 
2.17.1