1 files changed, 106 insertions, 0 deletions
diff --git a/library/std/src/sys/pal/unix/alloc.rs b/library/std/src/sys/pal/unix/alloc.rs
new file mode 100644
index 00000000000..af0089978ec
--- /dev/null
+++ b/library/std/src/sys/pal/unix/alloc.rs
@@ -0,0 +1,106 @@
+use crate::alloc::{GlobalAlloc, Layout, System};
+use crate::ptr;
+use crate::sys::common::alloc::{realloc_fallback, MIN_ALIGN};
+
+#[stable(feature = "alloc_system_type", since = "1.28.0")]
+unsafe impl GlobalAlloc for System {
+    #[inline]
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        // jemalloc provides alignment less than MIN_ALIGN for small allocations.
+        // So only rely on MIN_ALIGN if size >= align.
+        // Also see <https://github.com/rust-lang/rust/issues/45955> and
+        // <https://github.com/rust-lang/rust/issues/62251#issuecomment-507580914>.
+        if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
+            libc::malloc(layout.size()) as *mut u8
+        } else {
+            #[cfg(target_os = "macos")]
+            {
+                if layout.align() > (1 << 31) {
+                    return ptr::null_mut();
+                }
+            }
+            aligned_malloc(&layout)
+        }
+    }
+
+    #[inline]
+    unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
+        // See the comment above in `alloc` for why this check looks the way it does.
+        if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
+            libc::calloc(layout.size(), 1) as *mut u8
+        } else {
+            let ptr = self.alloc(layout);
+            if !ptr.is_null() {
+                ptr::write_bytes(ptr, 0, layout.size());
+            }
+            ptr
+        }
+    }
+
+    #[inline]
+    unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
+        libc::free(ptr as *mut libc::c_void)
+    }
+
+    #[inline]
+    unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
+        if layout.align() <= MIN_ALIGN && layout.align() <= new_size {
+            libc::realloc(ptr as *mut libc::c_void, new_size) as *mut u8
+        } else {
+            realloc_fallback(self, ptr, layout, new_size)
+        }
+    }
+}
+
+cfg_if::cfg_if! {
+    if #[cfg(any(
+        target_os = "android",
+        target_os = "illumos",
+        target_os = "redox",
+        target_os = "solaris",
+        target_os = "espidf",
+        target_os = "horizon",
+        target_os = "vita",
+    ))] {
+        #[inline]
+        unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
+            // On android we currently target API level 9 which unfortunately
+            // doesn't have the `posix_memalign` API used below. Instead we use
+            // `memalign`, but this unfortunately has the property on some systems
+            // where the memory returned cannot be deallocated by `free`!
+            //
+            // Upon closer inspection, however, this appears to work just fine with
+            // Android, so for this platform we should be fine to call `memalign`
+            // (which is present in API level 9). Some helpful references could
+            // possibly be chromium using memalign [1], attempts at documenting that
+            // memalign + free is ok [2] [3], or the current source of chromium
+            // which still uses memalign on android [4].
+            //
+            // [1]: https://codereview.chromium.org/10796020/
+            // [2]: https://code.google.com/p/android/issues/detail?id=35391
+            // [3]: https://bugs.chromium.org/p/chromium/issues/detail?id=138579
+            // [4]: https://chromium.googlesource.com/chromium/src/base/+/master/
+            //                                       /memory/aligned_memory.cc
+            libc::memalign(layout.align(), layout.size()) as *mut u8
+        }
+    } else if #[cfg(target_os = "wasi")] {
+        #[inline]
+        unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
+            // C11 aligned_alloc requires that the size be a multiple of the alignment.
+            // Layout already checks that the size rounded up doesn't overflow isize::MAX.
+            let align = layout.align();
+            let size = layout.size().next_multiple_of(align);
+            libc::aligned_alloc(align, size) as *mut u8
+        }
+    } else {
+        #[inline]
+        unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
+            let mut out = ptr::null_mut();
+            // posix_memalign requires that the alignment be a multiple of `sizeof(void*)`.
+            // Since these are all powers of 2, we can just use max.
+            let align = layout.align().max(crate::mem::size_of::<usize>());
+            let ret = libc::posix_memalign(&mut out, align, layout.size());
+            if ret != 0 { ptr::null_mut() } else { out as *mut u8 }
+        }
+    }
+}