helpers: Add AlignedBuffer

AlignedBuffer is a helper class that manages the livetime of a memory region, allocated using
a certain alignment. Like Box, it handles deallocation when the object isn't used anymore.

Author: seijikun

uefi/src/mem/aligned_buffer.rs

@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+
+use alloc::alloc::{alloc, dealloc, Layout, LayoutError};
+use core::error::Error;
+use core::fmt;
+
+/// Helper class to maintain the lifetime of a memory region allocated with a non-standard alignment.
+/// Facilitates RAII to properly deallocate when lifetime of the object ends.
+///
+/// Note: This uses the global Rust allocator under the hood.
+#[derive(Debug)]
+pub struct AlignedBuffer {
+    ptr: *mut u8,
+    layout: Layout,
+}
+
+impl AlignedBuffer {
+    /// Allocate a new memory region with the requested len and alignment.
+    pub fn from_size_align(len: usize, alignment: usize) -> Result<Self, LayoutError> {
+        let layout = Layout::from_size_align(len, alignment)?;
+        let ptr = unsafe { alloc(layout) };
+        Ok(Self { ptr, layout })
+    }
+
+    /// Get a pointer to the aligned memory region managed by this instance.
+    #[must_use]
+    pub const fn ptr(&self) -> *const u8 {
+        self.ptr.cast_const()
+    }
+
+    /// Get a mutable pointer to the aligned memory region managed by this instance.
+    #[must_use]
+    pub fn ptr_mut(&mut self) -> *mut u8 {
+        self.ptr
+    }
+
+    /// Get the size of the aligned memory region managed by this instance.
+    #[must_use]
+    pub const fn size(&self) -> usize {
+        self.layout.size()
+    }
+
+    /// Fill the aligned memory region with data from the given buffer.
+    ///
+    /// The length of `src` must be the same as `self`.
+    pub fn copy_from_slice(&mut self, src: &[u8]) {
+        assert_eq!(self.size(), src.len());
+        unsafe {
+            self.ptr.copy_from(src.as_ptr(), src.len());
+        }
+    }
+
+    /// Check the buffer's alignment against the `required_alignment`.
+    pub fn check_alignment(&self, required_alignment: usize) -> Result<(), AlignmentError> {
+        //TODO: use bfr.addr() when it's available
+        if (self.ptr as usize) % required_alignment != 0 {
+            return Err(AlignmentError); //TODO: use >is_aligned_to< when it's available
+        }
+        Ok(())
+    }
+}
+
+impl Drop for AlignedBuffer {
+    fn drop(&mut self) {
+        unsafe {
+            dealloc(self.ptr, self.layout);
+        }
+    }
+}
+
+/// The `AlignmentError` is returned if a user-provided buffer doesn't fulfill alignment requirements.
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct AlignmentError;
+impl Error for AlignmentError {}
+impl fmt::Display for AlignmentError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("Buffer alignment does not fulfill requirements.")
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::AlignedBuffer;
+
+    #[test]
+    fn test_invalid_arguments() {
+        // invalid alignments, valid len
+        for request_alignment in [0, 3, 5, 7, 9] {
+            for request_len in [1, 32, 64, 128, 1024] {
+                assert!(AlignedBuffer::alloc(request_len, request_alignment).is_err());
+            }
+        }
+    }
+
+    #[test]
+    fn test_allocation_alignment() {
+        for request_alignment in [1, 2, 4, 8, 16, 32, 64, 128] {
+            for request_len in [1 as usize, 32, 64, 128, 1024] {
+                let buffer = AlignedBuffer::alloc(request_len, request_alignment).unwrap();
+                assert_eq!(buffer.ptr() as usize % request_alignment, 0);
+                assert_eq!(buffer.len(), request_len);
+            }
+        }
+    }
+}

uefi/src/mem/mod.rs

@@ -14,6 +14,11 @@ pub(crate) mod util;
 #[cfg(feature = "alloc")]
 pub(crate) use util::*;
 
+#[cfg(feature = "alloc")]
+mod aligned_buffer;
+#[cfg(feature = "alloc")]
+pub use aligned_buffer::{AlignedBuffer, AlignmentError};
+
 /// Wrapper for memory allocated with UEFI's pool allocator. The memory is freed
 /// on drop.
 #[derive(Debug)]