allocators: don’t assume MIN_ALIGN for small sizes

src/liballoc/tests/heap.rs

@@ -0,0 +1,45 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use alloc_system::System;
+use std::heap::{Heap, Alloc, Layout};
+
+/// https://github.com/rust-lang/rust/issues/45955
+///
+/// Note that `#[global_allocator]` is not used,
+/// so `liballoc_jemalloc` is linked (on some platforms).
+#[test]
+fn alloc_system_overaligned_request() {
+    check_overalign_requests(System)
+}
+
+#[test]
+fn std_heap_overaligned_request() {
+    check_overalign_requests(Heap)
+}
+
+fn check_overalign_requests<T: Alloc>(mut allocator: T) {
+    let size = 8;
+    let align = 16; // greater than size
+    let iterations = 100;
+    unsafe {
+        let pointers: Vec<_> = (0..iterations).map(|_| {
+            allocator.alloc(Layout::from_size_align(size, align).unwrap()).unwrap()
+        }).collect();
+        for &ptr in &pointers {
+            assert_eq!((ptr as usize) % align, 0, "Got a pointer less aligned than requested")
+        }
+
+        // Clean up
+        for &ptr in &pointers {
+            allocator.dealloc(ptr, Layout::from_size_align(size, align).unwrap())
+        }
+    }
+}

src/liballoc/tests/lib.rs

@@ -10,6 +10,8 @@
 
 #![deny(warnings)]
 
+#![feature(allocator_api)]
+#![feature(alloc_system)]
 #![feature(attr_literals)]
 #![feature(box_syntax)]
 #![feature(inclusive_range_syntax)]
@@ -29,6 +31,7 @@
 #![feature(unboxed_closures)]
 #![feature(unicode)]
 
+extern crate alloc_system;
 extern crate std_unicode;
 extern crate rand;
 
@@ -39,6 +42,7 @@ mod binary_heap;
 mod btree;
 mod cow_str;
 mod fmt;
+mod heap;
 mod linked_list;
 mod slice;
 mod str;

src/liballoc_jemalloc/lib.rs

@@ -72,8 +72,7 @@ mod contents {
     const MALLOCX_ZERO: c_int = 0x40;
 
     // The minimum alignment guaranteed by the architecture. This value is used to
-    // add fast paths for low alignment values. In practice, the alignment is a
-    // constant at the call site and the branch will be optimized out.
+    // add fast paths for low alignment values.
     #[cfg(all(any(target_arch = "arm",
                   target_arch = "mips",
                   target_arch = "powerpc")))]
@@ -92,8 +91,8 @@ mod contents {
         a.trailing_zeros() as c_int
     }
 
-    fn align_to_flags(align: usize) -> c_int {
-        if align <= MIN_ALIGN {
+    fn align_to_flags(align: usize, size: usize) -> c_int {
+        if align <= MIN_ALIGN && align <= size {
             0
         } else {
             mallocx_align(align)
@@ -111,7 +110,7 @@ mod contents {
     pub unsafe extern fn __rde_alloc(size: usize,
                                      align: usize,
                                      err: *mut u8) -> *mut u8 {
-        let flags = align_to_flags(align);
+        let flags = align_to_flags(align, size);
         let ptr = mallocx(size as size_t, flags) as *mut u8;
         if ptr.is_null() {
             let layout = Layout::from_size_align_unchecked(size, align);
@@ -132,7 +131,7 @@ mod contents {
     pub unsafe extern fn __rde_dealloc(ptr: *mut u8,
                                        size: usize,
                                        align: usize) {
-        let flags = align_to_flags(align);
+        let flags = align_to_flags(align, size);
         sdallocx(ptr as *mut c_void, size, flags);
     }
 
@@ -142,7 +141,7 @@ mod contents {
                                            min: *mut usize,
                                            max: *mut usize) {
         let layout = &*(layout as *const Layout);
-        let flags = align_to_flags(layout.align());
+        let flags = align_to_flags(layout.align(), layout.size());
         let size = nallocx(layout.size(), flags) as usize;
         *min = layout.size();
         if size > 0 {
@@ -166,7 +165,7 @@ mod contents {
             return 0 as *mut u8
         }
 
-        let flags = align_to_flags(new_align);
+        let flags = align_to_flags(new_align, new_size);
         let ptr = rallocx(ptr as *mut c_void, new_size, flags) as *mut u8;
         if ptr.is_null() {
             let layout = Layout::from_size_align_unchecked(new_size, new_align);
@@ -181,10 +180,10 @@ mod contents {
     pub unsafe extern fn __rde_alloc_zeroed(size: usize,
                                             align: usize,
                                             err: *mut u8) -> *mut u8 {
-        let ptr = if align <= MIN_ALIGN {
+        let ptr = if align <= MIN_ALIGN && align <= size {
             calloc(size as size_t, 1) as *mut u8
         } else {
-            let flags = align_to_flags(align) | MALLOCX_ZERO;
+            let flags = align_to_flags(align, size) | MALLOCX_ZERO;
             mallocx(size as size_t, flags) as *mut u8
         };
         if ptr.is_null() {
@@ -203,7 +202,7 @@ mod contents {
                                             err: *mut u8) -> *mut u8 {
         let p = __rde_alloc(size, align, err);
         if !p.is_null() {
-            let flags = align_to_flags(align);
+            let flags = align_to_flags(align, size);
             *excess = nallocx(size, flags) as usize;
         }
         return p
@@ -220,7 +219,7 @@ mod contents {
                                               err: *mut u8) -> *mut u8 {
         let p = __rde_realloc(ptr, old_size, old_align, new_size, new_align, err);
         if !p.is_null() {
-            let flags = align_to_flags(new_align);
+            let flags = align_to_flags(new_align, new_size);
             *excess = nallocx(new_size, flags) as usize;
         }
         p
@@ -244,7 +243,7 @@ mod contents {
                                                new_size: usize,
                                                new_align: usize) -> u8 {
         if old_align == new_align {
-            let flags = align_to_flags(new_align);
+            let flags = align_to_flags(new_align, new_size);
             (xallocx(ptr as *mut c_void, new_size, 0, flags) == new_size) as u8
         } else {
             0

src/liballoc_system/lib.rs

@@ -25,8 +25,7 @@
 #![rustc_alloc_kind = "lib"]
 
 // The minimum alignment guaranteed by the architecture. This value is used to
-// add fast paths for low alignment values. In practice, the alignment is a
-// constant at the call site and the branch will be optimized out.
+// add fast paths for low alignment values.
 #[cfg(all(any(target_arch = "x86",
               target_arch = "arm",
               target_arch = "mips",
@@ -132,7 +131,7 @@ mod platform {
     unsafe impl<'a> Alloc for &'a System {
         #[inline]
         unsafe fn alloc(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
-            let ptr = if layout.align() <= MIN_ALIGN {
+            let ptr = if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
                 libc::malloc(layout.size()) as *mut u8
             } else {
                 aligned_malloc(&layout)
@@ -148,7 +147,7 @@ mod platform {
         unsafe fn alloc_zeroed(&mut self, layout: Layout)
             -> Result<*mut u8, AllocErr>
         {
-            if layout.align() <= MIN_ALIGN {
+            if layout.align() <= MIN_ALIGN && layout.align() <= layout.size() {
                 let ptr = libc::calloc(layout.size(), 1) as *mut u8;
                 if !ptr.is_null() {
                     Ok(ptr)
@@ -180,7 +179,7 @@ mod platform {
                 })
             }
 
-            if new_layout.align() <= MIN_ALIGN {
+            if new_layout.align() <= MIN_ALIGN  && new_layout.align() <= new_layout.size(){
                 let ptr = libc::realloc(ptr as *mut libc::c_void, new_layout.size());
                 if !ptr.is_null() {
                     Ok(ptr as *mut u8)