library/std/src/sys/unix/alloc.rs

   1 use crate::alloc::{GlobalAlloc, Layout, System};
   2 use crate::ptr;
   3 use crate::sys_common::alloc::{realloc_fallback, MIN_ALIGN};
   4
   5 #[stable(feature = "alloc_system_type", since = "1.28.0")]
   6 unsafe impl GlobalAlloc for System {
   7     #[inline]
   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
  15         } else {
  16             #[cfg(target_os = "macos")]
  17             {
  18                 if layout.align() > (1 << 31) {
  19                     return ptr::null_mut();
  20                 }
  21             }
  22             aligned_malloc(&layout)
  23         }
  24     }
  25
  26     #[inline]
  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
  31         } else {
  32             let ptr = self.alloc(layout);
  33             if !ptr.is_null() {
  34                 ptr::write_bytes(ptr, 0, layout.size());
  35             }
  36             ptr
  37         }
  38     }
  39
  40     #[inline]
  41     unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
  42         libc::free(ptr as *mut libc::c_void)
  43     }
  44
  45     #[inline]
  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
  49         } else {
  50             realloc_fallback(self, ptr, layout, new_size)
  51         }
  52     }
  53 }
  54
  55 cfg_if::cfg_if! {
  56     if #[cfg(any(
  57         target_os = "android",
  58         target_os = "illumos",
  59         target_os = "redox",
  60         target_os = "solaris"
  61     ))] {
  62         #[inline]
  63         unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
  64             // On android we currently target API level 9 which unfortunately
  65             // doesn't have the `posix_memalign` API used below. Instead we use
  66             // `memalign`, but this unfortunately has the property on some systems
  67             // where the memory returned cannot be deallocated by `free`!
  68             //
  69             // Upon closer inspection, however, this appears to work just fine with
  70             // Android, so for this platform we should be fine to call `memalign`
  71             // (which is present in API level 9). Some helpful references could
  72             // possibly be chromium using memalign [1], attempts at documenting that
  73             // memalign + free is ok [2] [3], or the current source of chromium
  74             // which still uses memalign on android [4].
  75             //
  76             // [1]: https://codereview.chromium.org/10796020/
  77             // [2]: https://code.google.com/p/android/issues/detail?id=35391
  78             // [3]: https://bugs.chromium.org/p/chromium/issues/detail?id=138579
  79             // [4]: https://chromium.googlesource.com/chromium/src/base/+/master/
  80             //                                       /memory/aligned_memory.cc
  81             libc::memalign(layout.align(), layout.size()) as *mut u8
  82         }
  83     } else if #[cfg(target_os = "wasi")] {
  84         #[inline]
  85         unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
  86             libc::aligned_alloc(layout.align(), layout.size()) as *mut u8
  87         }
  88     } else {
  89         #[inline]
  90         unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
  91             let mut out = ptr::null_mut();
  92             // posix_memalign requires that the alignment be a multiple of `sizeof(void*)`.
  93             // Since these are all powers of 2, we can just use max.
  94             let align = layout.align().max(crate::mem::size_of::<usize>());
  95             let ret = libc::posix_memalign(&mut out, align, layout.size());
  96             if ret != 0 { ptr::null_mut() } else { out as *mut u8 }
  97         }
  98     }
  99 }