From 7161da589e7e938742246068d09413b5f690543e Mon Sep 17 00:00:00 2001
From: Andrew Bresticker <abrestic@rivosinc.com>
Date: Fri, 23 Dec 2022 12:28:05 -0500
Subject: [PATCH] Vm: Forward legacy put_char() to host

Like the debug console, this should get forwarded to the VM's host rather
than having Salus print directly to the console.

Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
---
 src/host_vm.rs                   |  3 +++
 src/vm.rs                        | 11 +++--------
 test-workloads/src/bin/tellus.rs |  3 +++
 3 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/src/host_vm.rs b/src/host_vm.rs
index 37914dbb..c47b7636 100644
--- a/src/host_vm.rs
+++ b/src/host_vm.rs
@@ -431,6 +431,9 @@ impl HostVmRunner {
                                 // Can't do anything about errors right now.
                                 let _ = self.handle_put_string(&vm, addr, len);
                             }
+                            Ok(PutChar(c)) => {
+                                print!("{}", c as u8 as char);
+                            }
                             _ => {
                                 println!("Unhandled ECALL from host");
                                 return ControlFlow::Break(());
diff --git a/src/vm.rs b/src/vm.rs
index fd56514c..7e4ebb4e 100644
--- a/src/vm.rs
+++ b/src/vm.rs
@@ -193,7 +193,6 @@ impl From<SbiError> for EcallError {
 
 #[derive(Clone, Copy, Debug)]
 enum EcallAction {
-    LegacyOk,
     Unhandled,
     Continue(SbiReturn),
     Break(VmExitCause, SbiReturn),
@@ -489,9 +488,6 @@ impl<'a, T: GuestStagePagingMode> FinalizedVm<'a, T> {
             match exit {
                 VmCpuTrap::Ecall(Some(sbi_msg)) => {
                     match self.handle_ecall(sbi_msg, &mut active_vcpu) {
-                        EcallAction::LegacyOk => {
-                            active_vcpu.set_ecall_result(Legacy(0));
-                        }
                         EcallAction::Unhandled => {
                             active_vcpu.set_ecall_result(Standard(SbiReturn::from(
                                 SbiError::NotSupported,
@@ -705,10 +701,9 @@ impl<'a, T: GuestStagePagingMode> FinalizedVm<'a, T> {
     /// Handles ecalls from the guest.
     fn handle_ecall(&self, msg: SbiMessage, active_vcpu: &mut ActiveVmCpu<T>) -> EcallAction {
         match msg {
-            SbiMessage::PutChar(c) => {
-                // put char - legacy command
-                print!("{}", c as u8 as char);
-                EcallAction::LegacyOk
+            SbiMessage::PutChar(_) => {
+                // TODO: Let the host set the return value and forward it to the guest.
+                EcallAction::Break(VmExitCause::ResumableEcall(msg), SbiReturn::success(0))
             }
             SbiMessage::Reset(ResetFunction::Reset { .. }) => {
                 EcallAction::Break(VmExitCause::FatalEcall(msg), SbiReturn::success(0))
diff --git a/test-workloads/src/bin/tellus.rs b/test-workloads/src/bin/tellus.rs
index 21db5435..727fda21 100644
--- a/test-workloads/src/bin/tellus.rs
+++ b/test-workloads/src/bin/tellus.rs
@@ -643,6 +643,9 @@ extern "C" fn kernel_init(hart_id: u64, fdt_addr: u64) {
                                 len,
                             );
                         }
+                        Ok(PutChar(c)) => {
+                            print!("{}", c as u8 as char);
+                        }
                         _ => {
                             println!("Unexpected ECALL from guest");
                             break;