From 7062610abade962824019b902532bc389e30fe35 Mon Sep 17 00:00:00 2001
From: Gwilym Kuiper <gw@ilym.me>
Date: Mon, 16 Aug 2021 21:02:55 +0100
Subject: [PATCH] Start a basic allocator with a super simple test

---
 agb/src/agb_alloc/mod.rs | 76 ++++++++++++++++++++++++++++++++++++++++
 agb/src/lib.rs           |  6 +++-
 2 files changed, 81 insertions(+), 1 deletion(-)
 create mode 100644 agb/src/agb_alloc/mod.rs

diff --git a/agb/src/agb_alloc/mod.rs b/agb/src/agb_alloc/mod.rs
new file mode 100644
index 00000000..6908892e
--- /dev/null
+++ b/agb/src/agb_alloc/mod.rs
@@ -0,0 +1,76 @@
+use core::alloc::{GlobalAlloc, Layout};
+
+use super::interrupt::Mutex;
+
+extern "C" {
+    static __ewram_data_end: usize;
+}
+
+fn get_data_end() -> usize {
+    // TODO: This seems completely wrong, but without the &, rust generates
+    // a double dereference :/. Maybe a bug in nightly?
+    (unsafe { &__ewram_data_end }) as *const _ as usize
+}
+
+struct BumpAllocator {
+    current_ptr: Mutex<*mut u8>,
+}
+
+impl BumpAllocator {
+    fn alloc_safe(&self, layout: Layout) -> *mut u8 {
+        let mut current_ptr = self.current_ptr.lock();
+
+        let mut ptr = *current_ptr as usize;
+
+        if ptr == 0 {
+            ptr = get_data_end();
+        }
+
+        let alignment_bitmask = layout.align() - 1;
+        let fixup = ptr & alignment_bitmask;
+
+        let amount_to_add = layout.align() - fixup;
+
+        let resulting_ptr = ptr + amount_to_add;
+        *current_ptr = (resulting_ptr + layout.size()) as *mut _;
+
+        resulting_ptr as *mut _
+    }
+}
+
+unsafe impl GlobalAlloc for BumpAllocator {
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        self.alloc_safe(layout)
+    }
+
+    unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {}
+}
+
+#[alloc_error_handler]
+fn alloc_error(layout: Layout) -> ! {
+    panic!(
+        "Failed to allocate size {} with alignment {}",
+        layout.size(),
+        layout.align()
+    );
+}
+
+#[global_allocator]
+static GLOBAL_ALLOC: BumpAllocator = BumpAllocator {
+    current_ptr: Mutex::new(core::ptr::null_mut()),
+};
+
+#[cfg(test)]
+mod test {
+    use alloc::boxed::Box;
+
+    #[test_case]
+    fn test_box(_gba: &mut crate::Gba) {
+        let first_box = Box::new(1);
+        let second_box = Box::new(2);
+
+        assert!(&*first_box as *const _ < &*second_box as *const _);
+        assert_eq!(*first_box, 1);
+        assert_eq!(*second_box, 2);
+    }
+}
diff --git a/agb/src/lib.rs b/agb/src/lib.rs
index cb2a98fd..38a8f443 100644
--- a/agb/src/lib.rs
+++ b/agb/src/lib.rs
@@ -4,15 +4,17 @@
 #![feature(asm)]
 #![deny(clippy::all)]
 #![feature(custom_test_frameworks)]
+#![feature(alloc_error_handler)]
 #![test_runner(crate::test_runner)]
 #![reexport_test_harness_main = "test_main"]
-
 //! # agb
 //! `agb` is a library for making games on the Game Boy Advance using the Rust
 //! programming language. It attempts to be a high level abstraction over the
 //! internal workings of the Game Boy Advance whilst still being high
 //! performance and memory efficient.
 
+extern crate alloc;
+
 /// Implements everything relating to things that are displayed on screen.
 pub mod display;
 /// Button inputs to the system.
@@ -32,6 +34,8 @@ pub mod mgba;
 pub mod number;
 mod single;
 
+mod agb_alloc;
+
 /// System BIOS calls / syscalls.
 pub mod syscall;