Move volatile_store and ensure alignment (rust-lang#794)

* Move `volatile_store` and ensure alignment

* Create util function for concurrency warnings

* Add positive and negative test cases

* Emit concurrency warning with macro

src/kani-compiler/rustc_codegen_kani/src/codegen/intrinsic.rs

@@ -1,15 +1,24 @@
 // Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 //! this module handles intrinsics
-use tracing::{debug, warn};
-
 use crate::GotocCtx;
 use cbmc::goto_program::{BuiltinFn, Expr, Location, Stmt, Type};
 use rustc_middle::mir::Place;
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::Instance;
 use rustc_middle::ty::{self, Ty, TyS};
 use rustc_span::Span;
+use tracing::{debug, warn};
+
+macro_rules! emit_concurrency_warning {
+    ($intrinsic: expr, $loc: expr) => {{
+        warn!(
+            "Kani does not support concurrency for now. `{}` in {} treated as a sequential operation.",
+            $intrinsic,
+            $loc.short_string()
+        );
+    }};
+}
 
 struct SizeAlign {
     size: Expr,
@@ -279,8 +288,8 @@ impl<'tcx> GotocCtx<'tcx> {
         // Note: Atomic arithmetic operations wrap around on overflow.
         macro_rules! codegen_atomic_binop {
             ($op: ident) => {{
-                warn!("Kani does not support concurrency for now. {} treated as a sequential operation.", intrinsic);
                 let loc = self.codegen_span_option(span);
+                emit_concurrency_warning!(intrinsic, loc);
                 let var1_ref = fargs.remove(0);
                 let var1 = var1_ref.dereference();
                 let tmp = self.gen_temp_variable(var1.typ().clone(), loc.clone()).to_expr();
@@ -519,6 +528,10 @@ impl<'tcx> GotocCtx<'tcx> {
             "volatile_copy_memory" => codegen_intrinsic_copy!(Memmove),
             "volatile_copy_nonoverlapping_memory" => codegen_intrinsic_copy!(Memcpy),
             "volatile_load" => self.codegen_expr_to_place(p, fargs.remove(0).dereference()),
+            "volatile_store" => {
+                assert!(self.place_ty(p).is_unit());
+                self.codegen_volatile_store(instance, intrinsic, fargs, loc)
+            }
             "wrapping_add" => codegen_wrapping_op!(plus),
             "wrapping_mul" => codegen_wrapping_op!(mul),
             "wrapping_sub" => codegen_wrapping_op!(sub),
@@ -657,10 +670,7 @@ impl<'tcx> GotocCtx<'tcx> {
         p: &Place<'tcx>,
         loc: Location,
     ) -> Stmt {
-        warn!(
-            "Kani does not support concurrency for now. {} treated as a sequential operation.",
-            intrinsic
-        );
+        emit_concurrency_warning!(intrinsic, loc);
         let var1_ref = fargs.remove(0);
         let var1 = var1_ref.dereference().with_location(loc.clone());
         let res_stmt = self.codegen_expr_to_place(p, var1);
@@ -688,10 +698,7 @@ impl<'tcx> GotocCtx<'tcx> {
         p: &Place<'tcx>,
         loc: Location,
     ) -> Stmt {
-        warn!(
-            "Kani does not support concurrency for now. {} treated as a sequential operation.",
-            intrinsic
-        );
+        emit_concurrency_warning!(intrinsic, loc);
         let var1_ref = fargs.remove(0);
         let var1 = var1_ref.dereference().with_location(loc.clone());
         let tmp = self.gen_temp_variable(var1.typ().clone(), loc.clone()).to_expr();
@@ -727,10 +734,7 @@ impl<'tcx> GotocCtx<'tcx> {
         p: &Place<'tcx>,
         loc: Location,
     ) -> Stmt {
-        warn!(
-            "Kani does not support concurrency for now. {} treated as a sequential operation.",
-            intrinsic
-        );
+        emit_concurrency_warning!(intrinsic, loc);
         let var1_ref = fargs.remove(0);
         let var1 = var1_ref.dereference().with_location(loc.clone());
         let tmp = self.gen_temp_variable(var1.typ().clone(), loc.clone()).to_expr();
@@ -743,10 +747,7 @@ impl<'tcx> GotocCtx<'tcx> {
 
     /// Atomic no-ops (e.g., atomic_fence) are transformed into SKIP statements
     fn codegen_atomic_noop(&mut self, intrinsic: &str, loc: Location) -> Stmt {
-        warn!(
-            "Kani does not support concurrency for now. {} treated as a sequential operation.",
-            intrinsic
-        );
+        emit_concurrency_warning!(intrinsic, loc);
         let skip_stmt = Stmt::skip(loc.clone());
         Stmt::atomic_block(vec![skip_stmt], loc)
     }
@@ -1005,4 +1006,27 @@ impl<'tcx> GotocCtx<'tcx> {
             .collect();
         self.codegen_expr_to_place(p, Expr::vector_expr(cbmc_ret_ty, elems))
     }
+
+    /// A volatile write of a memory location:
+    /// https://doc.rust-lang.org/std/ptr/fn.write_volatile.html
+    ///
+    /// Undefined behavior if any of these conditions are violated:
+    ///  * `dst` must be valid for writes (done by `--pointer-check`)
+    ///  * `dst` must be properly aligned (done by `align_check` below)
+    fn codegen_volatile_store(
+        &mut self,
+        instance: Instance<'tcx>,
+        intrinsic: &str,
+        mut fargs: Vec<Expr>,
+        loc: Location,
+    ) -> Stmt {
+        emit_concurrency_warning!(intrinsic, loc);
+        let dst = fargs.remove(0);
+        let src = fargs.remove(0);
+        let typ = instance.substs.type_at(0);
+        let align = self.is_aligned(typ, dst.clone());
+        let align_check = Stmt::assert(align, "`dst` is properly aligned", loc.clone());
+        let expr = dst.dereference().assign(src, loc.clone());
+        Stmt::block(vec![align_check, expr], loc)
+    }
 }

src/kani-compiler/rustc_codegen_kani/src/overrides/hooks.rs

@@ -461,10 +461,8 @@ impl<'tcx> GotocHook<'tcx> for PtrWrite {
         let name = with_no_trimmed_paths(|| tcx.def_path_str(instance.def_id()));
         name == "core::ptr::write"
             || name == "core::ptr::write_unaligned"
-            || name == "core::ptr::write_volatile"
             || name == "std::ptr::write"
             || name == "std::ptr::write_unaligned"
-            || name == "std::ptr::write_volatile"
     }
 
     fn handle(

src/kani-compiler/rustc_codegen_kani/src/utils/utils.rs

@@ -4,6 +4,8 @@ use super::super::codegen::TypeExt;
 use crate::GotocCtx;
 use cbmc::btree_string_map;
 use cbmc::goto_program::{Expr, ExprValue, Location, Stmt, SymbolTable, Type};
+use rustc_middle::ty::layout::LayoutOf;
+use rustc_middle::ty::TyS;
 use tracing::debug;
 
 // Should move into rvalue
@@ -67,6 +69,16 @@ impl<'tcx> GotocCtx<'tcx> {
         Expr::statement_expression(body, t).with_location(loc)
     }
 
+    /// Generates an expression `((dst as usize) % align_of(T) == 0`
+    /// to determine if `dst` is aligned.
+    pub fn is_aligned(&mut self, typ: &'tcx TyS<'_>, dst: Expr) -> Expr {
+        let layout = self.layout_of(typ);
+        let align = Expr::int_constant(layout.align.abi.bytes(), Type::size_t());
+        let cast_dst = dst.cast_to(Type::size_t());
+        let zero = Type::size_t().zero();
+        cast_dst.rem(align).eq(zero)
+    }
+
     pub fn unsupported_msg(item: &str, url: Option<&str>) -> String {
         let mut s = format!("{} is not currently supported by Kani", item);
         if url.is_some() {

tests/kani/Intrinsics/Volatile/store.rs

@@ -0,0 +1,27 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+// Check that `volatile_store` passes when it writes to an aligned value.
+// This example is similar to the one that appears in the documentation for
+// `write_unaligned`:
+// https://doc.rust-lang.org/std/ptr/fn.write_unaligned.html
+#![feature(core_intrinsics)]
+
+// In contrast to the `Packed` struct in `store_fail.rs`, this struct includes
+// padding so that each field is aligned.
+struct NonPacked {
+    _padding: u8,
+    unaligned: u32,
+}
+
+fn main() {
+    let mut packed: NonPacked = unsafe { std::mem::zeroed() };
+    // Take the address of a 32-bit integer which is not aligned.
+    // In contrast to `&packed.unaligned as *mut _`, this has no undefined behavior.
+    let unaligned = std::ptr::addr_of_mut!(packed.unaligned);
+
+    // Store the value with `volatile_store`.
+    // This includes an alignment check for `unaligned` which should pass.
+    unsafe { std::intrinsics::volatile_store(unaligned, 42) };
+    assert!(packed.unaligned == 42);
+}

tests/kani/Intrinsics/Volatile/store_fail.rs

@@ -0,0 +1,29 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+// kani-verify-fail
+
+// Check that `volatile_store` fails when it writes to an unaligned value.
+// This example is similar to the one that appears in the documentation for
+// `write_unaligned`:
+// https://doc.rust-lang.org/std/ptr/fn.write_unaligned.html
+#![feature(core_intrinsics)]
+
+// `repr(packed)` forces the struct to be stripped of any padding and only align
+// its fields to a byte.
+#[repr(packed)]
+struct Packed {
+    _padding: u8,
+    unaligned: u32,
+}
+
+fn main() {
+    let mut packed: Packed = unsafe { std::mem::zeroed() };
+    // Take the address of a 32-bit integer which is not aligned.
+    // In contrast to `&packed.unaligned as *mut _`, this has no undefined behavior.
+    let unaligned = std::ptr::addr_of_mut!(packed.unaligned);
+
+    // Store the value with `volatile_store`.
+    // This includes an alignment check for `unaligned` which should fail.
+    unsafe { std::intrinsics::volatile_store(unaligned, 42) };
+    assert!(packed.unaligned == 42);
+}