diff --git a/os1-ref/src/sbi.rs b/os1-ref/src/sbi.rs
index 751a4d2..8d5c37b 100644
--- a/os1-ref/src/sbi.rs
+++ b/os1-ref/src/sbi.rs
@@ -10,6 +10,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os1/src/sbi.rs b/os1/src/sbi.rs
index 751a4d2..8d5c37b 100644
--- a/os1/src/sbi.rs
+++ b/os1/src/sbi.rs
@@ -10,6 +10,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os2-ref/src/sbi.rs b/os2-ref/src/sbi.rs
index 751a4d2..8d5c37b 100644
--- a/os2-ref/src/sbi.rs
+++ b/os2-ref/src/sbi.rs
@@ -10,6 +10,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os2/src/sbi.rs b/os2/src/sbi.rs
index 751a4d2..8d5c37b 100644
--- a/os2/src/sbi.rs
+++ b/os2/src/sbi.rs
@@ -10,6 +10,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os3-ref/src/sbi.rs b/os3-ref/src/sbi.rs
index 4af7620..3b58a23 100644
--- a/os3-ref/src/sbi.rs
+++ b/os3-ref/src/sbi.rs
@@ -13,6 +13,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os3/src/sbi.rs b/os3/src/sbi.rs
index 6dcad4e..376cd07 100644
--- a/os3/src/sbi.rs
+++ b/os3/src/sbi.rs
@@ -10,6 +10,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os4-ref/src/sbi.rs b/os4-ref/src/sbi.rs
index 4af7620..3b58a23 100644
--- a/os4-ref/src/sbi.rs
+++ b/os4-ref/src/sbi.rs
@@ -13,6 +13,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os4/src/sbi.rs b/os4/src/sbi.rs
index 6dcad4e..376cd07 100644
--- a/os4/src/sbi.rs
+++ b/os4/src/sbi.rs
@@ -10,6 +10,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os5-ref/src/sbi.rs b/os5-ref/src/sbi.rs
index 4af7620..3b58a23 100644
--- a/os5-ref/src/sbi.rs
+++ b/os5-ref/src/sbi.rs
@@ -13,6 +13,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os5/src/sbi.rs b/os5/src/sbi.rs
index 6dcad4e..376cd07 100644
--- a/os5/src/sbi.rs
+++ b/os5/src/sbi.rs
@@ -10,6 +10,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os6-ref/src/sbi.rs b/os6-ref/src/sbi.rs
index 4af7620..3b58a23 100644
--- a/os6-ref/src/sbi.rs
+++ b/os6-ref/src/sbi.rs
@@ -13,6 +13,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os6/src/sbi.rs b/os6/src/sbi.rs
index 4af7620..3b58a23 100644
--- a/os6/src/sbi.rs
+++ b/os6/src/sbi.rs
@@ -13,6 +13,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os7-ref/src/sbi.rs b/os7-ref/src/sbi.rs
index 4af7620..3b58a23 100644
--- a/os7-ref/src/sbi.rs
+++ b/os7-ref/src/sbi.rs
@@ -13,6 +13,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os7/src/sbi.rs b/os7/src/sbi.rs
index 4af7620..3b58a23 100644
--- a/os7/src/sbi.rs
+++ b/os7/src/sbi.rs
@@ -13,6 +13,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os8-ref/src/sbi.rs b/os8-ref/src/sbi.rs
index 4af7620..3b58a23 100644
--- a/os8-ref/src/sbi.rs
+++ b/os8-ref/src/sbi.rs
@@ -13,6 +13,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,
diff --git a/os8/src/sbi.rs b/os8/src/sbi.rs
index 4af7620..3b58a23 100644
--- a/os8/src/sbi.rs
+++ b/os8/src/sbi.rs
@@ -13,6 +13,7 @@ fn sbi_call(which: usize, arg0: usize, arg1: usize, arg2: usize) -> usize {
     let mut ret;
     unsafe {
         core::arch::asm!(
+            "li x16, 0",
             "ecall",
             inlateout("x10") arg0 => ret,
             in("x11") arg1,