feat: initialize Kurdistan SDK - independent fork of Polkadot SDK

substrate/primitives/io/src/global_alloc_wasm.rs

@@ -0,0 +1,85 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use core::{
+	alloc::{GlobalAlloc, Layout},
+	ptr,
+};
+
+/// The type used to store the offset between the real pointer and the returned pointer.
+type Offset = u16;
+
+/// The length of [`Offset`].
+const OFFSET_LENGTH: usize = core::mem::size_of::<Offset>();
+
+/// Allocator used by Substrate from within the runtime.
+///
+/// The allocator needs to align the returned pointer to given layout. We assume that on the host
+/// side the freeing-bump allocator is used with a fixed alignment of `8` and a `HEADER_SIZE` of
+/// `8`. The freeing-bump allocator is storing the header in the 8 bytes before the actual pointer
+/// returned by `alloc`. The problem is that the runtime not only sees pointers allocated by this
+/// `RuntimeAllocator`, but also pointers allocated by the host. The header is stored as a
+/// little-endian `u64`. The allocation header consists of 8 bytes. The first four bytes (as written
+/// in memory) are used to store the order of the allocation (or the link to the next slot, if
+/// unallocated). Then the least significant bit of the next byte determines whether a given slot is
+/// occupied or free, and the last three bytes are unused.
+///
+/// The `RuntimeAllocator` aligns the pointer to the required alignment before returning it to the
+/// user code. As we are assuming the freeing-bump allocator that already aligns by `8` by default,
+/// we only need to take care of alignments above `8`. The offset is stored in two bytes before the
+/// pointer that we return to the user. Depending on the alignment, we may write into the header,
+/// but given the assumptions above this should be no problem.
+struct RuntimeAllocator;
+
+#[global_allocator]
+static ALLOCATOR: RuntimeAllocator = RuntimeAllocator;
+
+unsafe impl GlobalAlloc for RuntimeAllocator {
+	unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+		let align = layout.align();
+		let size = layout.size();
+
+		// Allocate for the required size, plus a potential alignment.
+		//
+		// As the host side already aligns the pointer by `8`, we only need to account for any
+		// excess.
+		let ptr = crate::allocator::malloc((size + align.saturating_sub(8)) as u32);
+
+		// Calculate the required alignment.
+		let ptr_offset = ptr.align_offset(align);
+
+		// Should never happen, but just to be sure.
+		if ptr_offset > u16::MAX as usize || ptr.is_null() {
+			return ptr::null_mut();
+		}
+
+		// Align the pointer.
+		let ptr = ptr.add(ptr_offset);
+
+		unsafe {
+			(ptr.sub(OFFSET_LENGTH) as *mut Offset).write_unaligned(ptr_offset as Offset);
+		}
+
+		ptr
+	}
+
+	unsafe fn dealloc(&self, ptr: *mut u8, _: Layout) {
+		let offset = unsafe { (ptr.sub(OFFSET_LENGTH) as *const Offset).read_unaligned() };
+
+		crate::allocator::free(ptr.sub(offset as usize))
+	}
+}