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Diffstat (limited to 'library/std/src/sys/windows/alloc.rs')
| -rw-r--r-- | library/std/src/sys/windows/alloc.rs | 246 |
1 files changed, 246 insertions, 0 deletions
diff --git a/library/std/src/sys/windows/alloc.rs b/library/std/src/sys/windows/alloc.rs new file mode 100644 index 000000000..fdc81cdea --- /dev/null +++ b/library/std/src/sys/windows/alloc.rs @@ -0,0 +1,246 @@ +#![deny(unsafe_op_in_unsafe_fn)] + +use crate::alloc::{GlobalAlloc, Layout, System}; +use crate::ffi::c_void; +use crate::ptr; +use crate::sync::atomic::{AtomicPtr, Ordering}; +use crate::sys::c; +use crate::sys::common::alloc::{realloc_fallback, MIN_ALIGN}; + +#[cfg(test)] +mod tests; + +// Heap memory management on Windows is done by using the system Heap API (heapapi.h) +// See https://docs.microsoft.com/windows/win32/api/heapapi/ + +// Flag to indicate that the memory returned by `HeapAlloc` should be zeroed. +const HEAP_ZERO_MEMORY: c::DWORD = 0x00000008; + +extern "system" { + // Get a handle to the default heap of the current process, or null if the operation fails. + // + // SAFETY: Successful calls to this function within the same process are assumed to + // always return the same handle, which remains valid for the entire lifetime of the process. + // + // See https://docs.microsoft.com/windows/win32/api/heapapi/nf-heapapi-getprocessheap + fn GetProcessHeap() -> c::HANDLE; + + // Allocate a block of `dwBytes` bytes of memory from a given heap `hHeap`. + // The allocated memory may be uninitialized, or zeroed if `dwFlags` is + // set to `HEAP_ZERO_MEMORY`. + // + // Returns a pointer to the newly-allocated memory or null if the operation fails. + // The returned pointer will be aligned to at least `MIN_ALIGN`. + // + // SAFETY: + // - `hHeap` must be a non-null handle returned by `GetProcessHeap`. + // - `dwFlags` must be set to either zero or `HEAP_ZERO_MEMORY`. + // + // Note that `dwBytes` is allowed to be zero, contrary to some other allocators. + // + // See https://docs.microsoft.com/windows/win32/api/heapapi/nf-heapapi-heapalloc + fn HeapAlloc(hHeap: c::HANDLE, dwFlags: c::DWORD, dwBytes: c::SIZE_T) -> c::LPVOID; + + // Reallocate a block of memory behind a given pointer `lpMem` from a given heap `hHeap`, + // to a block of at least `dwBytes` bytes, either shrinking the block in place, + // or allocating at a new location, copying memory, and freeing the original location. + // + // Returns a pointer to the reallocated memory or null if the operation fails. + // The returned pointer will be aligned to at least `MIN_ALIGN`. + // If the operation fails the given block will never have been freed. + // + // SAFETY: + // - `hHeap` must be a non-null handle returned by `GetProcessHeap`. + // - `dwFlags` must be set to zero. + // - `lpMem` must be a non-null pointer to an allocated block returned by `HeapAlloc` or + // `HeapReAlloc`, that has not already been freed. + // If the block was successfully reallocated at a new location, pointers pointing to + // the freed memory, such as `lpMem`, must not be dereferenced ever again. + // + // Note that `dwBytes` is allowed to be zero, contrary to some other allocators. + // + // See https://docs.microsoft.com/windows/win32/api/heapapi/nf-heapapi-heaprealloc + fn HeapReAlloc( + hHeap: c::HANDLE, + dwFlags: c::DWORD, + lpMem: c::LPVOID, + dwBytes: c::SIZE_T, + ) -> c::LPVOID; + + // Free a block of memory behind a given pointer `lpMem` from a given heap `hHeap`. + // Returns a nonzero value if the operation is successful, and zero if the operation fails. + // + // SAFETY: + // - `hHeap` must be a non-null handle returned by `GetProcessHeap`. + // - `dwFlags` must be set to zero. + // - `lpMem` must be a pointer to an allocated block returned by `HeapAlloc` or `HeapReAlloc`, + // that has not already been freed. + // If the block was successfully freed, pointers pointing to the freed memory, such as `lpMem`, + // must not be dereferenced ever again. + // + // Note that `lpMem` is allowed to be null, which will not cause the operation to fail. + // + // See https://docs.microsoft.com/windows/win32/api/heapapi/nf-heapapi-heapfree + fn HeapFree(hHeap: c::HANDLE, dwFlags: c::DWORD, lpMem: c::LPVOID) -> c::BOOL; +} + +// Cached handle to the default heap of the current process. +// Either a non-null handle returned by `GetProcessHeap`, or null when not yet initialized or `GetProcessHeap` failed. +static HEAP: AtomicPtr<c_void> = AtomicPtr::new(ptr::null_mut()); + +// Get a handle to the default heap of the current process, or null if the operation fails. +// If this operation is successful, `HEAP` will be successfully initialized and contain +// a non-null handle returned by `GetProcessHeap`. +#[inline] +fn init_or_get_process_heap() -> c::HANDLE { + let heap = HEAP.load(Ordering::Relaxed); + if heap.is_null() { + // `HEAP` has not yet been successfully initialized + let heap = unsafe { GetProcessHeap() }; + if !heap.is_null() { + // SAFETY: No locking is needed because within the same process, + // successful calls to `GetProcessHeap` will always return the same value, even on different threads. + HEAP.store(heap, Ordering::Release); + + // SAFETY: `HEAP` contains a non-null handle returned by `GetProcessHeap` + heap + } else { + // Could not get the current process heap. + ptr::null_mut() + } + } else { + // SAFETY: `HEAP` contains a non-null handle returned by `GetProcessHeap` + heap + } +} + +// Get a non-null handle to the default heap of the current process. +// SAFETY: `HEAP` must have been successfully initialized. +#[inline] +unsafe fn get_process_heap() -> c::HANDLE { + HEAP.load(Ordering::Acquire) +} + +// Header containing a pointer to the start of an allocated block. +// SAFETY: Size and alignment must be <= `MIN_ALIGN`. +#[repr(C)] +struct Header(*mut u8); + +// Allocate a block of optionally zeroed memory for a given `layout`. +// SAFETY: Returns a pointer satisfying the guarantees of `System` about allocated pointers, +// or null if the operation fails. If this returns non-null `HEAP` will have been successfully +// initialized. +#[inline] +unsafe fn allocate(layout: Layout, zeroed: bool) -> *mut u8 { + let heap = init_or_get_process_heap(); + if heap.is_null() { + // Allocation has failed, could not get the current process heap. + return ptr::null_mut(); + } + + // Allocated memory will be either zeroed or uninitialized. + let flags = if zeroed { HEAP_ZERO_MEMORY } else { 0 }; + + if layout.align() <= MIN_ALIGN { + // SAFETY: `heap` is a non-null handle returned by `GetProcessHeap`. + // The returned pointer points to the start of an allocated block. + unsafe { HeapAlloc(heap, flags, layout.size()) as *mut u8 } + } else { + // Allocate extra padding in order to be able to satisfy the alignment. + let total = layout.align() + layout.size(); + + // SAFETY: `heap` is a non-null handle returned by `GetProcessHeap`. + let ptr = unsafe { HeapAlloc(heap, flags, total) as *mut u8 }; + if ptr.is_null() { + // Allocation has failed. + return ptr::null_mut(); + } + + // Create a correctly aligned pointer offset from the start of the allocated block, + // and write a header before it. + + let offset = layout.align() - (ptr.addr() & (layout.align() - 1)); + // SAFETY: `MIN_ALIGN` <= `offset` <= `layout.align()` and the size of the allocated + // block is `layout.align() + layout.size()`. `aligned` will thus be a correctly aligned + // pointer inside the allocated block with at least `layout.size()` bytes after it and at + // least `MIN_ALIGN` bytes of padding before it. + let aligned = unsafe { ptr.add(offset) }; + // SAFETY: Because the size and alignment of a header is <= `MIN_ALIGN` and `aligned` + // is aligned to at least `MIN_ALIGN` and has at least `MIN_ALIGN` bytes of padding before + // it, it is safe to write a header directly before it. + unsafe { ptr::write((aligned as *mut Header).offset(-1), Header(ptr)) }; + + // SAFETY: The returned pointer does not point to the to the start of an allocated block, + // but there is a header readable directly before it containing the location of the start + // of the block. + aligned + } +} + +// All pointers returned by this allocator have, in addition to the guarantees of `GlobalAlloc`, the +// following properties: +// +// If the pointer was allocated or reallocated with a `layout` specifying an alignment <= `MIN_ALIGN` +// the pointer will be aligned to at least `MIN_ALIGN` and point to the start of the allocated block. +// +// If the pointer was allocated or reallocated with a `layout` specifying an alignment > `MIN_ALIGN` +// the pointer will be aligned to the specified alignment and not point to the start of the allocated block. +// Instead there will be a header readable directly before the returned pointer, containing the actual +// location of the start of the block. +#[stable(feature = "alloc_system_type", since = "1.28.0")] +unsafe impl GlobalAlloc for System { + #[inline] + unsafe fn alloc(&self, layout: Layout) -> *mut u8 { + // SAFETY: Pointers returned by `allocate` satisfy the guarantees of `System` + let zeroed = false; + unsafe { allocate(layout, zeroed) } + } + + #[inline] + unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 { + // SAFETY: Pointers returned by `allocate` satisfy the guarantees of `System` + let zeroed = true; + unsafe { allocate(layout, zeroed) } + } + + #[inline] + unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) { + let block = { + if layout.align() <= MIN_ALIGN { + ptr + } else { + // The location of the start of the block is stored in the padding before `ptr`. + + // SAFETY: Because of the contract of `System`, `ptr` is guaranteed to be non-null + // and have a header readable directly before it. + unsafe { ptr::read((ptr as *mut Header).offset(-1)).0 } + } + }; + + // SAFETY: because `ptr` has been successfully allocated with this allocator, + // `HEAP` must have been successfully initialized. + let heap = unsafe { get_process_heap() }; + + // SAFETY: `heap` is a non-null handle returned by `GetProcessHeap`, + // `block` is a pointer to the start of an allocated block. + unsafe { HeapFree(heap, 0, block as c::LPVOID) }; + } + + #[inline] + unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 { + if layout.align() <= MIN_ALIGN { + // SAFETY: because `ptr` has been successfully allocated with this allocator, + // `HEAP` must have been successfully initialized. + let heap = unsafe { get_process_heap() }; + + // SAFETY: `heap` is a non-null handle returned by `GetProcessHeap`, + // `ptr` is a pointer to the start of an allocated block. + // The returned pointer points to the start of an allocated block. + unsafe { HeapReAlloc(heap, 0, ptr as c::LPVOID, new_size) as *mut u8 } + } else { + // SAFETY: `realloc_fallback` is implemented using `dealloc` and `alloc`, which will + // correctly handle `ptr` and return a pointer satisfying the guarantees of `System` + unsafe { realloc_fallback(self, ptr, layout, new_size) } + } + } +} |