fusee-cpp: add basic structural stubs

fusee_cpp/loader_stub/source/fusee_loader_main.cpp

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <exosphere.hpp>
+#include "fusee_loader_uncompress.hpp"
+#include "program_lz4.h"
+
+namespace ams::nxboot::loader {
+
+    namespace {
+
+        constexpr uintptr_t ProgramImageBase = 0x40001000;
+        constexpr uintptr_t ProgramImageEnd  = 0x4003D000;
+        constexpr size_t ProgramImageSizeMax = ProgramImageEnd - ProgramImageBase;
+
+        void CopyBackwards(void *dst, const void *src, size_t size) {
+            /* We want to copy 32-bits at a time from destination to source. */
+            const size_t words = util::DivideUp(size, sizeof(u32));
+
+            /* Convert to 32-bit pointers. */
+                  u32 *dst_32 = static_cast<u32 *>(dst) + words;
+            const u32 *src_32 = static_cast<const u32 *>(src) + words;
+
+            /* Copy data. */
+            for (size_t i = 0; i < words; ++i) {
+                *(--dst_32) = *(--src_32);
+            }
+        }
+
+    }
+
+    NORETURN void UncompressAndExecute(const void *program, size_t program_size) {
+        /* Relocate the compressed binary to a place where we can safely decompress it. */
+        void *relocated_program = reinterpret_cast<void *>(util::AlignDown(ProgramImageEnd - program_size, sizeof(u32)));
+        if (relocated_program != program) {
+            CopyBackwards(relocated_program, program, program_size);
+        }
+
+        /* Uncompress the program image. */
+        Uncompress(reinterpret_cast<void *>(ProgramImageBase), ProgramImageSizeMax, relocated_program, program_size);
+
+        /* Jump to the boot image. */
+        reinterpret_cast<void (*)()>(ProgramImageBase)();
+
+        /* We will never reach this point. */
+        __builtin_unreachable();
+    }
+
+}