rustc_mir_transform/
check_alignment.rs1use rustc_abi::Align;
2use rustc_index::IndexVec;
3use rustc_middle::mir::interpret::Scalar;
4use rustc_middle::mir::visit::PlaceContext;
5use rustc_middle::mir::*;
6use rustc_middle::ty::{Ty, TyCtxt};
7use rustc_session::Session;
8
9use crate::check_pointers::{BorrowedFieldProjectionMode, PointerCheck, check_pointers};
10
11pub(super) struct CheckAlignment;
12
13impl<'tcx> crate::MirPass<'tcx> for CheckAlignment {
14 fn is_enabled(&self, sess: &Session) -> bool {
15 sess.ub_checks()
16 }
17
18 fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
19 let excluded_pointees = [tcx.types.bool, tcx.types.i8, tcx.types.u8];
21
22 check_pointers(
26 tcx,
27 body,
28 &excluded_pointees,
29 insert_alignment_check,
30 BorrowedFieldProjectionMode::FollowProjections,
31 );
32 }
33
34 fn is_required(&self) -> bool {
35 true
36 }
37}
38
39fn insert_alignment_check<'tcx>(
42 tcx: TyCtxt<'tcx>,
43 pointer: Place<'tcx>,
44 pointee_ty: Ty<'tcx>,
45 _context: PlaceContext,
46 local_decls: &mut IndexVec<Local, LocalDecl<'tcx>>,
47 stmts: &mut Vec<Statement<'tcx>>,
48 source_info: SourceInfo,
49) -> PointerCheck<'tcx> {
50 let const_raw_ptr = Ty::new_imm_ptr(tcx, tcx.types.unit);
52 let rvalue = Rvalue::Cast(CastKind::PtrToPtr, Operand::Copy(pointer), const_raw_ptr);
53 let thin_ptr = local_decls.push(LocalDecl::with_source_info(const_raw_ptr, source_info)).into();
54 stmts.push(Statement::new(source_info, StatementKind::Assign(Box::new((thin_ptr, rvalue)))));
55
56 let rvalue = Rvalue::Cast(CastKind::Transmute, Operand::Copy(thin_ptr), tcx.types.usize);
58 let addr = local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
59 stmts.push(Statement::new(source_info, StatementKind::Assign(Box::new((addr, rvalue)))));
60
61 let alignment =
63 local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
64 let rvalue = Rvalue::NullaryOp(NullOp::AlignOf, pointee_ty);
65 stmts.push(Statement::new(source_info, StatementKind::Assign(Box::new((alignment, rvalue)))));
66
67 let alignment_mask =
69 local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
70 let one = Operand::Constant(Box::new(ConstOperand {
71 span: source_info.span,
72 user_ty: None,
73 const_: Const::Val(ConstValue::Scalar(Scalar::from_target_usize(1, &tcx)), tcx.types.usize),
74 }));
75 stmts.push(Statement::new(
76 source_info,
77 StatementKind::Assign(Box::new((
78 alignment_mask,
79 Rvalue::BinaryOp(BinOp::Sub, Box::new((Operand::Copy(alignment), one))),
80 ))),
81 ));
82
83 #[allow(irrefutable_let_patterns)]
86 if let max_align = tcx.sess.target.max_reliable_alignment()
87 && max_align < Align::MAX
88 {
89 let max_mask = max_align.bytes() - 1;
90 let max_mask = Operand::Constant(Box::new(ConstOperand {
91 span: source_info.span,
92 user_ty: None,
93 const_: Const::Val(
94 ConstValue::Scalar(Scalar::from_target_usize(max_mask, &tcx)),
95 tcx.types.usize,
96 ),
97 }));
98 stmts.push(Statement::new(
99 source_info,
100 StatementKind::Assign(Box::new((
101 alignment_mask,
102 Rvalue::BinaryOp(
103 BinOp::BitAnd,
104 Box::new((Operand::Copy(alignment_mask), max_mask)),
105 ),
106 ))),
107 ));
108 }
109
110 let alignment_bits =
112 local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
113 stmts.push(Statement::new(
114 source_info,
115 StatementKind::Assign(Box::new((
116 alignment_bits,
117 Rvalue::BinaryOp(
118 BinOp::BitAnd,
119 Box::new((Operand::Copy(addr), Operand::Copy(alignment_mask))),
120 ),
121 ))),
122 ));
123
124 let is_ok = local_decls.push(LocalDecl::with_source_info(tcx.types.bool, source_info)).into();
126 let zero = Operand::Constant(Box::new(ConstOperand {
127 span: source_info.span,
128 user_ty: None,
129 const_: Const::Val(ConstValue::Scalar(Scalar::from_target_usize(0, &tcx)), tcx.types.usize),
130 }));
131 stmts.push(Statement::new(
132 source_info,
133 StatementKind::Assign(Box::new((
134 is_ok,
135 Rvalue::BinaryOp(BinOp::Eq, Box::new((Operand::Copy(alignment_bits), zero.clone()))),
136 ))),
137 ));
138
139 PointerCheck {
142 cond: Operand::Copy(is_ok),
143 assert_kind: Box::new(AssertKind::MisalignedPointerDereference {
144 required: Operand::Copy(alignment),
145 found: Operand::Copy(addr),
146 }),
147 }
148}