From ecd2d00f47ce69ff20699e4a4e0677edc75d5ef3 Mon Sep 17 00:00:00 2001
From: Sean Cross <sean@xobs.io>
Date: Wed, 14 Oct 2020 10:54:23 +0800
Subject: [PATCH] kernel: fix return_scalar2

This call did not work, because it wasn't properly returning control to
the parent process.

Signed-off-by: Sean Cross <sean@xobs.io>
---
 kernel/src/syscall.rs | 36 +++++++++++++++++++++++++-----------
 1 file changed, 25 insertions(+), 11 deletions(-)

diff --git a/kernel/src/syscall.rs b/kernel/src/syscall.rs
index 7f9a3e9d3..4b506bd29 100644
--- a/kernel/src/syscall.rs
+++ b/kernel/src/syscall.rs
@@ -345,8 +345,8 @@ fn return_scalar(pid: PID, _tid: TID, sender: MessageSender, arg: usize) -> SysC
 }
 
 fn return_scalar2(
-    pid: PID,
-    _tid: TID,
+    server_pid: PID,
+    server_tid: TID,
     sender: MessageSender,
     arg1: usize,
     arg2: usize,
@@ -360,7 +360,7 @@ fn return_scalar2(
         let server = ss
             .server_from_sidx_mut(sidx)
             .ok_or(xous_kernel::Error::ServerNotFound)?;
-        if server.pid != pid {
+        if server.pid != server_pid {
             return Err(xous_kernel::Error::ServerNotFound);
         }
         let result = server.take_waiting_message(sender.idx, None)?;
@@ -387,14 +387,23 @@ fn return_scalar2(
                 return Err(xous_kernel::Error::ProcessNotFound);
             }
         };
+
+        // Handle the server's return value
+        ss.switch_from_thread(server_pid, server_tid)?;
+        ss.ready_thread(server_pid, server_tid)?;
+        ss.set_thread_result(
+            server_pid,
+            server_tid,
+            xous_kernel::Result::Ok,
+        )?;
+
+        // Switch to the client
         ss.ready_thread(client_pid, client_tid)?;
         ss.switch_to_thread(client_pid, Some(client_tid))?;
-        ss.set_thread_result(
-            client_pid,
-            client_tid,
-            xous_kernel::Result::Scalar2(arg1, arg2),
-        )?;
-        Ok(xous_kernel::Result::Ok)
+        #[cfg(not(baremetal))]
+        ss.set_thread_result(client_pid, client_tid, xous_kernel::Result::Scalar2(arg1, arg2))?;
+
+        Ok(xous_kernel::Result::Scalar2(arg1, arg2))
     })
 }
 
@@ -457,7 +466,12 @@ pub fn handle(pid: PID, tid: TID, call: SysCall) -> SysCallResult {
     print!("KERNEL({}:{}): Syscall {:?}", pid, tid, call);
     let result = handle_inner(pid, tid, call);
     #[cfg(feature = "debug-print")]
-    println!(" -> {:?}", result);
+    println!(
+        " -> ({}:{}) {:?}",
+        crate::arch::current_pid(),
+        crate::arch::process::Process::current().current_tid(),
+        result
+    );
     result
 }
 
@@ -680,7 +694,7 @@ pub fn handle_inner(pid: PID, tid: TID, call: SysCall) -> SysCallResult {
                 Err(xous_kernel::Error::ServerQueueFull) => {
                     arch::process::Process::with_current_mut(|p| p.retry_instruction(tid))?;
                     do_yield(pid, tid)
-                },
+                }
                 Err(e) => Err(e),
             }
         }