core: Add support for N3DS memory mappings (#5103)

* core: Add support for N3DS memory mappings

* Address review comments

src/core/loader/loader.h

@@ -105,13 +105,22 @@ public:
      * Loads the system mode that this application needs.
      * This function defaults to 2 (96MB allocated to the application) if it can't read the
      * information.
-     * @returns A pair with the optional system mode, and and the status.
+     * @returns A pair with the optional system mode, and the status.
      */
     virtual std::pair<std::optional<u32>, ResultStatus> LoadKernelSystemMode() {
         // 96MB allocated to the application.
         return std::make_pair(2, ResultStatus::Success);
     }
 
+    /**
+     * Loads the N3ds mode that this application uses.
+     * It defaults to 0 (O3DS default) if it can't read the information.
+     * @returns A pair with the optional N3ds mode, and the status.
+     */
+    virtual std::pair<std::optional<u8>, ResultStatus> LoadKernelN3dsMode() {
+        return std::make_pair(0, ResultStatus::Success);
+    }
+
     /**
      * Get whether this application is executable.
      * @param out_executable Reference to store the executable flag into.

src/core/loader/ncch.cpp

@@ -61,6 +61,19 @@ std::pair<std::optional<u32>, ResultStatus> AppLoader_NCCH::LoadKernelSystemMode
                           ResultStatus::Success);
 }
 
+std::pair<std::optional<u8>, ResultStatus> AppLoader_NCCH::LoadKernelN3dsMode() {
+    if (!is_loaded) {
+        ResultStatus res = base_ncch.Load();
+        if (res != ResultStatus::Success) {
+            return std::make_pair(std::optional<u8>{}, res);
+        }
+    }
+
+    // Set the system mode as the one from the exheader.
+    return std::make_pair(overlay_ncch->exheader_header.arm11_system_local_caps.n3ds_mode,
+                          ResultStatus::Success);
+}
+
 ResultStatus AppLoader_NCCH::LoadExec(std::shared_ptr<Kernel::Process>& process) {
     using Kernel::CodeSet;
 

src/core/loader/ncch.h

@@ -41,6 +41,8 @@ public:
      */
     std::pair<std::optional<u32>, ResultStatus> LoadKernelSystemMode() override;
 
+    std::pair<std::optional<u8>, ResultStatus> LoadKernelN3dsMode() override;
+
     ResultStatus IsExecutable(bool& out_executable) override;
 
     ResultStatus ReadCode(std::vector<u8>& buffer) override;