1 files changed, 88 insertions, 0 deletions
diff --git a/library/std/src/sys/alloc/unix.rs b/library/std/src/sys/alloc/unix.rs
new file mode 100644
index 00000000000..46ed7de7162
--- /dev/null
+++ b/library/std/src/sys/alloc/unix.rs
@@ -0,0 +1,88 @@
+use super::{realloc_fallback, MIN_ALIGN};
+use crate::alloc::{GlobalAlloc, Layout, System};
+use crate::ptr;
+
+#[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() {
+            unsafe { libc::malloc(layout.size()) as *mut u8 }
+        } else {
+            // `posix_memalign` returns a non-aligned value if supplied a very
+            // large alignment on older versions of Apple's platforms (unknown
+            // exactly which version range, but the issue is definitely
+            // present in macOS 10.14 and iOS 13.3).
+            //
+            // <https://github.com/rust-lang/rust/issues/30170>
+            #[cfg(target_vendor = "apple")]
+            {
+                if layout.align() > (1 << 31) {
+                    return ptr::null_mut();
+                }
+            }
+            unsafe { 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() {
+            unsafe { libc::calloc(layout.size(), 1) as *mut u8 }
+        } else {
+            let ptr = unsafe { self.alloc(layout) };
+            if !ptr.is_null() {
+                unsafe { ptr::write_bytes(ptr, 0, layout.size()) };
+            }
+            ptr
+        }
+    }
+
+    #[inline]
+    unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
+        unsafe { 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 {
+            unsafe { libc::realloc(ptr as *mut libc::c_void, new_size) as *mut u8 }
+        } else {
+            unsafe { realloc_fallback(self, ptr, layout, new_size) }
+        }
+    }
+}
+
+cfg_if::cfg_if! {
+    // We use posix_memalign wherever possible, but some targets have very incomplete POSIX coverage
+    // so we need a fallback for those.
+    if #[cfg(any(
+        target_os = "horizon",
+        target_os = "vita",
+    ))] {
+        #[inline]
+        unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
+            unsafe { libc::memalign(layout.align(), layout.size()) as *mut u8 }
+        }
+    } else {
+        #[inline]
+        unsafe fn aligned_malloc(layout: &Layout) -> *mut u8 {
+            let mut out = ptr::null_mut();
+            // We prefer posix_memalign over aligned_alloc since it is more widely available, and
+            // since with aligned_alloc, implementations are making almost arbitrary choices for
+            // which alignments are "supported", making it hard to use. For instance, some
+            // implementations require the size to be a multiple of the alignment (wasi emmalloc),
+            // while others require the alignment to be at least the pointer size (Illumos, macOS).
+            // posix_memalign only has one, clear requirement: 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 = unsafe { libc::posix_memalign(&mut out, align, layout.size()) };
+            if ret != 0 { ptr::null_mut() } else { out as *mut u8 }
+        }
+    }
+}