Apply the GPLv3 license

Copyright disclaimer and copyright note are prepending to a every source
file.

Add license section in the `README.md` file.

Create the LICENSE` file with license information.

Signed-off-by: Alexey Gavrilov <alexey.gavrilov@mail.com>

4 files changed, 72 insertions, 0 deletions

diff --git a/kernel/CMakeLists.txt b/kernel/CMakeLists.txt
index cd249d0..61b69c4 100644
--- a/kernel/CMakeLists.txt
+++ b/kernel/CMakeLists.txt
@@ -1,3 +1,21 @@
+#[[
+ * Copyright (c) 2026 Alexey Gavrilov <alexey.gavrilov@mail.com>
+ *
+ * This file is part of ObjectiveOS.
+ *
+ * ObjectiveOS is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later
+ * version.
+ *
+ * ObjectiveOS is distributed in the hope that 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
+ * ObjectiveOS. If not, see <https://www.gnu.org/licenses/>. 
+ ]]
+
 target_link_options(CXX_LINKER_REQUIREMENTS INTERFACE
     LINKER:-T${CMAKE_CURRENT_LIST_DIR}/linker.ld
 )
diff --git a/kernel/details/CMakeLists.txt b/kernel/details/CMakeLists.txt
index 881d360..ceab7f6 100644
--- a/kernel/details/CMakeLists.txt
+++ b/kernel/details/CMakeLists.txt
@@ -1,3 +1,21 @@
+#[[
+ * Copyright (c) 2026 Alexey Gavrilov <alexey.gavrilov@mail.com>
+ *
+ * This file is part of ObjectiveOS.
+ *
+ * ObjectiveOS is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later
+ * version.
+ *
+ * ObjectiveOS is distributed in the hope that 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
+ * ObjectiveOS. If not, see <https://www.gnu.org/licenses/>. 
+ ]]
+
 target_sources(CPUID
     PUBLIC
         FILE_SET HEADERS
diff --git a/kernel/details/Platform.h b/kernel/details/Platform.h
index 12a8353..03c4054 100644
--- a/kernel/details/Platform.h
+++ b/kernel/details/Platform.h
@@ -1,3 +1,21 @@
+/**
+ * Copyright (c) 2026 Alexey Gavrilov <alexey.gavrilov@mail.com>
+ *
+ * This file is part of ObjectiveOS.
+ *
+ * ObjectiveOS is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later
+ * version.
+ *
+ * ObjectiveOS is distributed in the hope that 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
+ * ObjectiveOS. If not, see <https://www.gnu.org/licenses/>. 
+ */
+
 #ifndef PLATHFORMDETAILS_H
 #define PLATHFORMDETAILS_H
 
diff --git a/kernel/kernel.cpp b/kernel/kernel.cpp
index c280755..4f85cf7 100644
--- a/kernel/kernel.cpp
+++ b/kernel/kernel.cpp
@@ -1,3 +1,21 @@
+/**
+ * Copyright (c) 2026 Alexey Gavrilov <alexey.gavrilov@mail.com>
+ *
+ * This file is part of ObjectiveOS.
+ *
+ * ObjectiveOS is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later
+ * version.
+ *
+ * ObjectiveOS is distributed in the hope that 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
+ * ObjectiveOS. If not, see <https://www.gnu.org/licenses/>. 
+ */
+
 
 #include "../arch/SecondaryInit.h"
 #include "../arch/x86/ic/Pic.h"