fix minimal alignment for system allocation functions

Author: RalfJung

src/shims/foreign_items.rs

@@ -51,6 +51,18 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         Ok(Some(this.load_mir(instance.def)?))
     }
 
+    /// Returns the minimum alignment for the target architecture.
+    fn min_align(&self) -> Align {
+        let this = self.eval_context_ref();
+        // List taken from `libstd/sys_common/alloc.rs`.
+        let min_align = match this.tcx.tcx.sess.target.target.arch.as_str() {
+            "x86" | "arm" | "mips" | "powerpc" | "powerpc64" | "asmjs" | "wasm32" => 8,
+            "x86_64" | "aarch64" | "mips64" | "s390x" | "sparc64" => 16,
+            arch => bug!("Unsupported target architecture: {}", arch),
+        };
+        Align::from_bytes(min_align).unwrap()
+    }
+
     fn malloc(
         &mut self,
         size: u64,
@@ -61,7 +73,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         if size == 0 {
             Scalar::from_int(0, this.pointer_size())
         } else {
-            let align = this.tcx.data_layout.pointer_align.abi;
+            let align = this.min_align();
             let ptr = this.memory_mut().allocate(Size::from_bytes(size), align, MiriMemoryKind::C.into());
             if zero_init {
                 // We just allocated this, the access cannot fail
@@ -94,7 +106,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         new_size: u64,
     ) -> InterpResult<'tcx, Scalar<Tag>> {
         let this = self.eval_context_mut();
-        let align = this.tcx.data_layout.pointer_align.abi;
+        let align = this.min_align();
         if old_ptr.is_null_ptr(this) {
             if new_size == 0 {
                 Ok(Scalar::from_int(0, this.pointer_size()))

tests/run-pass/heap_allocator.rs

@@ -6,35 +6,47 @@ use std::alloc::{Global, Alloc, Layout, System};
 use std::slice;
 
 fn check_alloc<T: Alloc>(mut allocator: T) { unsafe {
-    let layout = Layout::from_size_align(20, 4).unwrap();
-    let a = allocator.alloc(layout).unwrap();
-    allocator.dealloc(a, layout);
+    for &align in &[4, 8, 16, 32] {
+        let layout = Layout::from_size_align(20, align).unwrap();
 
-    let p1 = allocator.alloc_zeroed(layout).unwrap();
+        for _ in 0..32 {
+            let a = allocator.alloc(layout).unwrap();
+            assert_eq!(a.as_ptr() as usize % align, 0, "pointer is incorrectly aligned");
+            allocator.dealloc(a, layout);
+        }
+
+        let p1 = allocator.alloc_zeroed(layout).unwrap();
+        assert_eq!(p1.as_ptr() as usize % align, 0, "pointer is incorrectly aligned");
 
-    let p2 = allocator.realloc(p1, Layout::from_size_align(20, 4).unwrap(), 40).unwrap();
-    let slice = slice::from_raw_parts(p2.as_ptr(), 20);
-    assert_eq!(&slice, &[0_u8; 20]);
+        let p2 = allocator.realloc(p1, layout, 40).unwrap();
+        let layout = Layout::from_size_align(40, align).unwrap();
+        assert_eq!(p2.as_ptr() as usize % align, 0, "pointer is incorrectly aligned");
+        let slice = slice::from_raw_parts(p2.as_ptr(), 20);
+        assert_eq!(&slice, &[0_u8; 20]);
 
-    // old size == new size
-    let p3 = allocator.realloc(p2, Layout::from_size_align(40, 4).unwrap(), 40).unwrap();
-    let slice = slice::from_raw_parts(p3.as_ptr(), 20);
-    assert_eq!(&slice, &[0_u8; 20]);
+        // old size == new size
+        let p3 = allocator.realloc(p2, layout, 40).unwrap();
+        assert_eq!(p3.as_ptr() as usize % align, 0, "pointer is incorrectly aligned");
+        let slice = slice::from_raw_parts(p3.as_ptr(), 20);
+        assert_eq!(&slice, &[0_u8; 20]);
 
-    // old size > new size
-    let p4 = allocator.realloc(p3, Layout::from_size_align(40, 4).unwrap(), 10).unwrap();
-    let slice = slice::from_raw_parts(p4.as_ptr(), 10);
-    assert_eq!(&slice, &[0_u8; 10]);
+        // old size > new size
+        let p4 = allocator.realloc(p3, layout, 10).unwrap();
+        let layout = Layout::from_size_align(10, align).unwrap();
+        assert_eq!(p4.as_ptr() as usize % align, 0, "pointer is incorrectly aligned");
+        let slice = slice::from_raw_parts(p4.as_ptr(), 10);
+        assert_eq!(&slice, &[0_u8; 10]);
 
-    allocator.dealloc(p4, Layout::from_size_align(10, 4).unwrap());
+        allocator.dealloc(p4, layout);
+    }
 } }
 
 fn check_overalign_requests<T: Alloc>(mut allocator: T) {
     let size = 8;
-    // Greater than `size`.
-    let align = 16;
+    // Greater than `size`, and also greater than `MIN_ALIGN`.
+    let align = 32;
 
-    let iterations = 5;
+    let iterations = 32;
     unsafe {
         let pointers: Vec<_> = (0..iterations).map(|_| {
             allocator.alloc(Layout::from_size_align(size, align).unwrap()).unwrap()