diff options
| -rw-r--r-- | rust/kernel/alloc/allocator_test.rs | 178 |
1 files changed, 171 insertions, 7 deletions
diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs index 1b2642c547ec..7fff308d02dc 100644 --- a/rust/kernel/alloc/allocator_test.rs +++ b/rust/kernel/alloc/allocator_test.rs @@ -2,20 +2,184 @@ #![allow(missing_docs)] -use super::{AllocError, Allocator, Flags}; +use super::{flags::*, AllocError, Allocator, Flags}; use core::alloc::Layout; +use core::cmp; +use core::mem; +use core::ptr; use core::ptr::NonNull; -pub struct Kmalloc; +pub struct Cmalloc; +pub type Kmalloc = Cmalloc; pub type Vmalloc = Kmalloc; pub type KVmalloc = Kmalloc; -unsafe impl Allocator for Kmalloc { +extern "C" { + #[link_name = "aligned_alloc"] + fn libc_aligned_alloc(align: usize, size: usize) -> *mut core::ffi::c_void; + + #[link_name = "free"] + fn libc_free(ptr: *mut core::ffi::c_void); +} + +struct CmallocData { + // The actual size as requested through `Cmalloc::alloc` or `Cmalloc::realloc`. + size: usize, + // The offset from the pointer returned to the caller of `Cmalloc::alloc` or `Cmalloc::realloc` + // to the actual base address of the allocation. + offset: usize, +} + +impl Cmalloc { + /// Adjust the size and alignment such that we can additionally store `CmallocData` right + /// before the actual data described by `layout`. + /// + /// Example: + /// + /// For `CmallocData` assume an alignment of 8 and a size of 16. + /// For `layout` assume and alignment of 16 and a size of 64. + /// + /// 0 16 32 96 + /// |----------------|----------------|------------------------------------------------| + /// empty CmallocData data + /// + /// For this example the returned `Layout` has an alignment of 32 and a size of 96. + fn layout_adjust(layout: Layout) -> Result<Layout, AllocError> { + let layout = layout.pad_to_align(); + + // Ensure that `CmallocData` fits into half the alignment. Additionally, this guarantees + // that advancing a pointer aligned to `align` by `align / 2` we still satisfy or exceed + // the alignment requested through `layout`. + let align = cmp::max( + layout.align(), + mem::size_of::<CmallocData>().next_power_of_two(), + ) * 2; + + // Add the additional space required for `CmallocData`. + let size = layout.size() + mem::size_of::<CmallocData>(); + + Ok(Layout::from_size_align(size, align) + .map_err(|_| AllocError)? + .pad_to_align()) + } + + fn alloc_store_data(layout: Layout) -> Result<NonNull<u8>, AllocError> { + let requested_size = layout.size(); + + let layout = Self::layout_adjust(layout)?; + let min_align = layout.align() / 2; + + // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or + // exceeds the given size and alignment requirements. + let raw_ptr = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8; + + let priv_ptr = NonNull::new(raw_ptr).ok_or(AllocError)?; + + // SAFETY: Advance the pointer by `min_align`. The adjustments from `Self::layout_adjust` + // ensure that after this operation the original size and alignment requirements are still + // satisfied or exceeded. + let ptr = unsafe { priv_ptr.as_ptr().add(min_align) }; + + // SAFETY: `min_align` is greater than or equal to the size of `CmallocData`, hence we + // don't exceed the allocation boundaries. + let data_ptr: *mut CmallocData = unsafe { ptr.sub(mem::size_of::<CmallocData>()) }.cast(); + + let data = CmallocData { + size: requested_size, + offset: min_align, + }; + + // SAFETY: `data_ptr` is properly aligned and within the allocation boundaries reserved for + // `CmallocData`. + unsafe { data_ptr.write(data) }; + + NonNull::new(ptr).ok_or(AllocError) + } + + /// # Safety + /// + /// `ptr` must have been previously allocated with `Self::alloc_store_data`. + unsafe fn data<'a>(ptr: NonNull<u8>) -> &'a CmallocData { + // SAFETY: `Self::alloc_store_data` stores the `CmallocData` right before the address + // returned to callers of `Self::alloc_store_data`. + let data_ptr: *mut CmallocData = + unsafe { ptr.as_ptr().sub(mem::size_of::<CmallocData>()) }.cast(); + + // SAFETY: The `CmallocData` has been previously stored at this offset with + // `Self::alloc_store_data`. + unsafe { &*data_ptr } + } + + /// # Safety + /// + /// This function must not be called more than once for the same allocation. + /// + /// `ptr` must have been previously allocated with `Self::alloc_store_data`. + unsafe fn free_read_data(ptr: NonNull<u8>) { + // SAFETY: `ptr` has been created by `Self::alloc_store_data`. + let data = unsafe { Self::data(ptr) }; + + // SAFETY: `ptr` has been created by `Self::alloc_store_data`. + let priv_ptr = unsafe { ptr.as_ptr().sub(data.offset) }; + + // SAFETY: `priv_ptr` has previously been allocatored with this `Allocator`. + unsafe { libc_free(priv_ptr.cast()) }; + } +} + +unsafe impl Allocator for Cmalloc { + fn alloc(layout: Layout, flags: Flags) -> Result<NonNull<[u8]>, AllocError> { + if layout.size() == 0 { + return Ok(NonNull::slice_from_raw_parts(NonNull::dangling(), 0)); + } + + let ptr = Self::alloc_store_data(layout)?; + + if flags.contains(__GFP_ZERO) { + // SAFETY: `Self::alloc_store_data` guarantees that `ptr` points to memory of at least + // `layout.size()` bytes. + unsafe { ptr.as_ptr().write_bytes(0, layout.size()) }; + } + + Ok(NonNull::slice_from_raw_parts(ptr, layout.size())) + } + unsafe fn realloc( - _ptr: Option<NonNull<u8>>, - _layout: Layout, - _flags: Flags, + ptr: Option<NonNull<u8>>, + layout: Layout, + flags: Flags, ) -> Result<NonNull<[u8]>, AllocError> { - panic!(); + let src: NonNull<u8> = if let Some(src) = ptr { + src.cast() + } else { + return Self::alloc(layout, flags); + }; + + if layout.size() == 0 { + // SAFETY: `src` has been created by `Self::alloc_store_data`. + unsafe { Self::free_read_data(src) }; + + return Ok(NonNull::slice_from_raw_parts(NonNull::dangling(), 0)); + } + + let dst = Self::alloc(layout, flags)?; + + // SAFETY: `src` has been created by `Self::alloc_store_data`. + let data = unsafe { Self::data(src) }; + + // SAFETY: `src` has previously been allocated with this `Allocator`; `dst` has just been + // newly allocated. Copy up to the smaller of both sizes. + unsafe { + ptr::copy_nonoverlapping( + src.as_ptr(), + dst.as_ptr().cast(), + cmp::min(layout.size(), data.size), + ) + }; + + // SAFETY: `src` has been created by `Self::alloc_store_data`. + unsafe { Self::free_read_data(src) }; + + Ok(dst) } } |