2 use crate::sys_common::alloc::{MIN_ALIGN, realloc_fallback};
3 use crate::alloc::{GlobalAlloc, Layout, System};
5 #[stable(feature = "alloc_system_type", since = "1.28.0")]
6 unsafe impl GlobalAlloc for System {
8 unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
9 // jemalloc provides alignment less than MIN_ALIGN for small allocations.
10 // So only rely on MIN_ALIGN if size >= align.
11 // Also see <https://github.com/rust-lang/rust/issues/45955> and
12 // <https://github.com/rust-lang/rust/issues/62251#issuecomment-507580914>.
13 if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
14 libc::malloc(layout.size()) as *mut u8
16 #[cfg(target_os = "macos")]
18 if layout.align() > (1 << 31) {
19 return ptr::null_mut()
22 aligned_malloc(&layout)
27 unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
28 // See the comment above in `alloc` for why this check looks the way it does.
29 if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
30 libc::calloc(layout.size(), 1) as *mut u8
32 let ptr = self.alloc(layout);
34 ptr::write_bytes(ptr, 0, layout.size());
41 unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
42 libc::free(ptr as *mut libc::c_void)
46 unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
47 if layout.align() <= MIN_ALIGN && layout.align() <= new_size {
48 libc::realloc(ptr as *mut libc::c_void, new_size) as *mut u8
50 realloc_fallback(self, ptr, layout, new_size)
55 #[cfg(any(target_os = "android",
58 target_os = "solaris"))]
60 unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
61 // On android we currently target API level 9 which unfortunately
62 // doesn't have the `posix_memalign` API used below. Instead we use
63 // `memalign`, but this unfortunately has the property on some systems
64 // where the memory returned cannot be deallocated by `free`!
66 // Upon closer inspection, however, this appears to work just fine with
67 // Android, so for this platform we should be fine to call `memalign`
68 // (which is present in API level 9). Some helpful references could
69 // possibly be chromium using memalign [1], attempts at documenting that
70 // memalign + free is ok [2] [3], or the current source of chromium
71 // which still uses memalign on android [4].
73 // [1]: https://codereview.chromium.org/10796020/
74 // [2]: https://code.google.com/p/android/issues/detail?id=35391
75 // [3]: https://bugs.chromium.org/p/chromium/issues/detail?id=138579
76 // [4]: https://chromium.googlesource.com/chromium/src/base/+/master/
77 // /memory/aligned_memory.cc
78 libc::memalign(layout.align(), layout.size()) as *mut u8
81 #[cfg(not(any(target_os = "android",
84 target_os = "solaris")))]
86 unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
87 let mut out = ptr::null_mut();
88 // posix_memalign requires that the alignment be a multiple of `sizeof(void*)`.
89 // Since these are all powers of 2, we can just use max.
90 let align = layout.align().max(crate::mem::size_of::<usize>());
91 let ret = libc::posix_memalign(&mut out, align, layout.size());