3 files changed, 43 insertions, 10 deletions

diff --git a/src/core/core.cpp b/src/core/core.cpp
index e95ae80da..f075ae7fa 100644
--- a/src/core/core.cpp
+++ b/src/core/core.cpp
@@ -562,6 +562,8 @@ struct System::Impl {
 
     std::array<Core::GPUDirtyMemoryManager, Core::Hardware::NUM_CPU_CORES>
         gpu_dirty_memory_write_manager{};
+
+    std::deque<std::vector<u8>> user_channel;
 };
 
 System::System() : impl{std::make_unique<Impl>(*this)} {}
@@ -1036,6 +1038,10 @@ void System::ExecuteProgram(std::size_t program_index) {
     }
 }
 
+std::deque<std::vector<u8>>& System::GetUserChannel() {
+    return impl->user_channel;
+}
+
 void System::RegisterExitCallback(ExitCallback&& callback) {
     impl->exit_callback = std::move(callback);
 }
diff --git a/src/core/core.h b/src/core/core.h
index a9ff9315e..fba312125 100644
--- a/src/core/core.h
+++ b/src/core/core.h
@@ -4,6 +4,7 @@
 #pragma once
 
 #include <cstddef>
+#include <deque>
 #include <functional>
 #include <memory>
 #include <mutex>
@@ -459,6 +460,12 @@ public:
      */
     void ExecuteProgram(std::size_t program_index);
 
+    /**
+     * Gets a reference to the user channel stack.
+     * It is used to transfer data between programs.
+     */
+    [[nodiscard]] std::deque<std::vector<u8>>& GetUserChannel();
+
     /// Type used for the frontend to designate a callback for System to exit the application.
     using ExitCallback = std::function<void()>;
 
diff --git a/src/core/hle/service/am/am.cpp b/src/core/hle/service/am/am.cpp
index 42e00c30a..f9c4f9678 100644
--- a/src/core/hle/service/am/am.cpp
+++ b/src/core/hle/service/am/am.cpp
@@ -1518,12 +1518,26 @@ void IApplicationFunctions::PopLaunchParameter(HLERequestContext& ctx) {
     IPC::RequestParser rp{ctx};
     const auto kind = rp.PopEnum<LaunchParameterKind>();
 
-    LOG_WARNING(Service_AM, "(STUBBED) called, kind={:08X}", kind);
+    LOG_INFO(Service_AM, "called, kind={:08X}", kind);
 
     if (kind == LaunchParameterKind::UserChannel) {
-        LOG_ERROR(Service_AM, "Popping from UserChannel is not supported!");
+        auto channel = system.GetUserChannel();
+        if (channel.empty()) {
+            LOG_ERROR(Service_AM, "Attempted to load launch parameter but none was found!");
+            IPC::ResponseBuilder rb{ctx, 2};
+            rb.Push(AM::ResultNoDataInChannel);
+            return;
+        }
+
+        auto data = channel.back();
+        channel.pop_back();
+
+        IPC::ResponseBuilder rb{ctx, 2, 0, 1};
+        rb.Push(ResultSuccess);
+        rb.PushIpcInterface<IStorage>(system, std::move(data));
     } else if (kind == LaunchParameterKind::AccountPreselectedUser &&
                !launch_popped_account_preselect) {
+        // TODO: Verify this is hw-accurate
         LaunchParameterAccountPreselectedUser params{};
 
         params.magic = LAUNCH_PARAMETER_ACCOUNT_PRESELECTED_USER_MAGIC;
@@ -1535,7 +1549,6 @@ void IApplicationFunctions::PopLaunchParameter(HLERequestContext& ctx) {
         params.current_user = *uuid;
 
         IPC::ResponseBuilder rb{ctx, 2, 0, 1};
-
         rb.Push(ResultSuccess);
 
         std::vector<u8> buffer(sizeof(LaunchParameterAccountPreselectedUser));
@@ -1543,12 +1556,11 @@ void IApplicationFunctions::PopLaunchParameter(HLERequestContext& ctx) {
 
         rb.PushIpcInterface<IStorage>(system, std::move(buffer));
         launch_popped_account_preselect = true;
-        return;
+    } else {
+        LOG_ERROR(Service_AM, "Unknown launch parameter kind.");
+        IPC::ResponseBuilder rb{ctx, 2};
+        rb.Push(AM::ResultNoDataInChannel);
     }
-
-    LOG_ERROR(Service_AM, "Attempted to load launch parameter but none was found!");
-    IPC::ResponseBuilder rb{ctx, 2};
-    rb.Push(AM::ResultNoDataInChannel);
 }
 
 void IApplicationFunctions::CreateApplicationAndRequestToStartForQuest(HLERequestContext& ctx) {
@@ -1840,14 +1852,22 @@ void IApplicationFunctions::ExecuteProgram(HLERequestContext& ctx) {
 }
 
 void IApplicationFunctions::ClearUserChannel(HLERequestContext& ctx) {
-    LOG_WARNING(Service_AM, "(STUBBED) called");
+    LOG_DEBUG(Service_AM, "called");
+
+    system.GetUserChannel().clear();
 
     IPC::ResponseBuilder rb{ctx, 2};
     rb.Push(ResultSuccess);
 }
 
 void IApplicationFunctions::UnpopToUserChannel(HLERequestContext& ctx) {
-    LOG_WARNING(Service_AM, "(STUBBED) called");
+    LOG_DEBUG(Service_AM, "called");
+
+    IPC::RequestParser rp{ctx};
+    const auto storage = rp.PopIpcInterface<IStorage>().lock();
+    if (storage) {
+        system.GetUserChannel().push_back(storage->GetData());
+    }
 
     IPC::ResponseBuilder rb{ctx, 2};
     rb.Push(ResultSuccess);