1 // SPDX-License-Identifier: GPL-2.0 2 3 //! Allocator support. 4 5 use core::alloc::{GlobalAlloc, Layout}; 6 use core::ptr; 7 8 use crate::bindings; 9 10 struct KernelAllocator; 11 12 /// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment. 13 /// 14 /// # Safety 15 /// 16 /// - `ptr` can be either null or a pointer which has been allocated by this allocator. 17 /// - `new_layout` must have a non-zero size. 18 unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: bindings::gfp_t) -> *mut u8 { 19 // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first. 20 let layout = new_layout.pad_to_align(); 21 22 let mut size = layout.size(); 23 24 if layout.align() > bindings::BINDINGS_ARCH_SLAB_MINALIGN { 25 // The alignment requirement exceeds the slab guarantee, thus try to enlarge the size 26 // to use the "power-of-two" size/alignment guarantee (see comments in `kmalloc()` for 27 // more information). 28 // 29 // Note that `layout.size()` (after padding) is guaranteed to be a multiple of 30 // `layout.align()`, so `next_power_of_two` gives enough alignment guarantee. 31 size = size.next_power_of_two(); 32 } 33 34 // SAFETY: 35 // - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the 36 // function safety requirement. 37 // - `size` is greater than 0 since it's either a `layout.size()` (which cannot be zero 38 // according to the function safety requirement) or a result from `next_power_of_two()`. 39 unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags) as *mut u8 } 40 } 41 42 unsafe impl GlobalAlloc for KernelAllocator { 43 unsafe fn alloc(&self, layout: Layout) -> *mut u8 { 44 // `krealloc()` is used instead of `kmalloc()` because the latter is 45 // an inline function and cannot be bound to as a result. 46 unsafe { bindings::krealloc(ptr::null(), layout.size(), bindings::GFP_KERNEL) as *mut u8 } 47 } 48 49 unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) { 50 unsafe { 51 bindings::kfree(ptr as *const core::ffi::c_void); 52 } 53 } 54 } 55 56 #[global_allocator] 57 static ALLOCATOR: KernelAllocator = KernelAllocator; 58 59 // `rustc` only generates these for some crate types. Even then, we would need 60 // to extract the object file that has them from the archive. For the moment, 61 // let's generate them ourselves instead. 62 // 63 // Note: Although these are *safe* functions, they are called by the compiler 64 // with parameters that obey the same `GlobalAlloc` function safety 65 // requirements: size and align should form a valid layout, and size is 66 // greater than 0. 67 // 68 // Note that `#[no_mangle]` implies exported too, nowadays. 69 #[no_mangle] 70 fn __rust_alloc(size: usize, align: usize) -> *mut u8 { 71 // SAFETY: See assumption above. 72 let layout = unsafe { Layout::from_size_align_unchecked(size, align) }; 73 74 // SAFETY: `ptr::null_mut()` is null, per assumption above the size of `layout` is greater 75 // than 0. 76 unsafe { krealloc_aligned(ptr::null_mut(), layout, bindings::GFP_KERNEL) } 77 } 78 79 #[no_mangle] 80 fn __rust_dealloc(ptr: *mut u8, _size: usize, _align: usize) { 81 unsafe { bindings::kfree(ptr as *const core::ffi::c_void) }; 82 } 83 84 #[no_mangle] 85 fn __rust_realloc(ptr: *mut u8, _old_size: usize, align: usize, new_size: usize) -> *mut u8 { 86 // SAFETY: See assumption above. 87 let new_layout = unsafe { Layout::from_size_align_unchecked(new_size, align) }; 88 89 // SAFETY: Per assumption above, `ptr` is allocated by `__rust_*` before, and the size of 90 // `new_layout` is greater than 0. 91 unsafe { krealloc_aligned(ptr, new_layout, bindings::GFP_KERNEL) } 92 } 93 94 #[no_mangle] 95 fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8 { 96 // SAFETY: See assumption above. 97 let layout = unsafe { Layout::from_size_align_unchecked(size, align) }; 98 99 // SAFETY: `ptr::null_mut()` is null, per assumption above the size of `layout` is greater 100 // than 0. 101 unsafe { 102 krealloc_aligned( 103 ptr::null_mut(), 104 layout, 105 bindings::GFP_KERNEL | bindings::__GFP_ZERO, 106 ) 107 } 108 } 109