diff --git a/kernel/src/arch/riscv/trap.rs b/kernel/src/arch/riscv/trap.rs
index c836e62..78dbf6d 100644
--- a/kernel/src/arch/riscv/trap.rs
+++ b/kernel/src/arch/riscv/trap.rs
@@ -110,16 +110,16 @@ impl TrapContextOps for TrapContext {
     }
 
     fn get_reg(&self, index: usize) -> usize {
-        // x10 ~ x17: Function arguments
+        // x9(a0) ~ x16(a7): Function arguments
         assert!(index < 8, "TrapContext get_reg index out of range");
-        self.gprs[index + 10]
+        self.gprs[index + 9]
     }
 
     fn set_reg(&mut self, index: usize, value: usize) {
-        // x10 ~ x17: Function arguments
-        // x10 ~ x11: Function return values
+        // x9(a0) ~ x16(a7): Function arguments
+        // x9(a0) ~ x10(a1): Function return values
         assert!(index < 8, "TrapContext set_reg index out of range");
-        self.gprs[index + 10] = value;
+        self.gprs[index + 9] = value;
     }
 }