[feat] introduce set_return_value API

Author: hky1999

src/exception.rs

@@ -1,8 +1,8 @@
 use aarch64_cpu::registers::{ESR_EL2, HCR_EL2, Readable, SCTLR_EL1, VTCR_EL2, VTTBR_EL2};
 
-use axaddrspace::GuestPhysAddr;
+use axaddrspace::{GuestPhysAddr, device::AccessWidth};
 use axerrno::{AxError, AxResult};
-use axvcpu::{AccessWidth, AxVCpuExitReason};
+use axvcpu::AxVCpuExitReason;
 
 use crate::TrapFrame;
 use crate::exception_utils::{

src/vcpu.rs

@@ -121,6 +121,11 @@ impl<H: AxVCpuHal> axvcpu::AxArchVCpu for Aarch64VCpu<H> {
     fn set_gpr(&mut self, idx: usize, val: usize) {
         self.ctx.set_gpr(idx, val);
     }
+
+    fn set_return_value(&mut self, val: usize) {
+        // Return value is stored in x0.
+        self.ctx.set_argument(val);
+    }
 }
 
 // Private function