rustc_mir_transform/
check_null.rs1use rustc_index::IndexVec;
2use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext};
3use rustc_middle::mir::*;
4use rustc_middle::ty::{Ty, TyCtxt};
5use rustc_session::Session;
6
7use crate::check_pointers::{BorrowedFieldProjectionMode, PointerCheck, check_pointers};
8
9pub(super) struct CheckNull;
10
11impl<'tcx> crate::MirPass<'tcx> for CheckNull {
12 fn is_enabled(&self, sess: &Session) -> bool {
13 sess.ub_checks()
14 }
15
16 fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
17 check_pointers(
18 tcx,
19 body,
20 &[],
21 insert_null_check,
22 BorrowedFieldProjectionMode::NoFollowProjections,
23 );
24 }
25
26 fn is_required(&self) -> bool {
27 true
28 }
29}
30
31fn insert_null_check<'tcx>(
32 tcx: TyCtxt<'tcx>,
33 pointer: Place<'tcx>,
34 pointee_ty: Ty<'tcx>,
35 context: PlaceContext,
36 local_decls: &mut IndexVec<Local, LocalDecl<'tcx>>,
37 stmts: &mut Vec<Statement<'tcx>>,
38 source_info: SourceInfo,
39) -> PointerCheck<'tcx> {
40 let const_raw_ptr = Ty::new_imm_ptr(tcx, tcx.types.unit);
42 let rvalue = Rvalue::Cast(CastKind::PtrToPtr, Operand::Copy(pointer), const_raw_ptr);
43 let thin_ptr = local_decls.push(LocalDecl::with_source_info(const_raw_ptr, source_info)).into();
44 stmts.push(Statement::new(source_info, StatementKind::Assign(Box::new((thin_ptr, rvalue)))));
45
46 let rvalue = Rvalue::Cast(CastKind::Transmute, Operand::Copy(thin_ptr), tcx.types.usize);
48 let addr = local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
49 stmts.push(Statement::new(source_info, StatementKind::Assign(Box::new((addr, rvalue)))));
50
51 let zero = Operand::Constant(Box::new(ConstOperand {
52 span: source_info.span,
53 user_ty: None,
54 const_: Const::Val(ConstValue::from_target_usize(0, &tcx), tcx.types.usize),
55 }));
56
57 let pointee_should_be_checked = match context {
58 PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow)
60 | PlaceContext::MutatingUse(MutatingUseContext::Borrow) => {
61 Operand::Constant(Box::new(ConstOperand {
63 span: source_info.span,
64 user_ty: None,
65 const_: Const::Val(ConstValue::from_bool(true), tcx.types.bool),
66 }))
67 }
68 _ => {
70 let rvalue = Rvalue::NullaryOp(NullOp::SizeOf, pointee_ty);
71 let sizeof_pointee =
72 local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
73 stmts.push(Statement::new(
74 source_info,
75 StatementKind::Assign(Box::new((sizeof_pointee, rvalue))),
76 ));
77
78 let is_pointee_not_zst =
80 local_decls.push(LocalDecl::with_source_info(tcx.types.bool, source_info)).into();
81 stmts.push(Statement::new(
82 source_info,
83 StatementKind::Assign(Box::new((
84 is_pointee_not_zst,
85 Rvalue::BinaryOp(
86 BinOp::Ne,
87 Box::new((Operand::Copy(sizeof_pointee), zero.clone())),
88 ),
89 ))),
90 ));
91
92 Operand::Copy(is_pointee_not_zst)
94 }
95 };
96
97 let is_null = local_decls.push(LocalDecl::with_source_info(tcx.types.bool, source_info)).into();
99 stmts.push(Statement::new(
100 source_info,
101 StatementKind::Assign(Box::new((
102 is_null,
103 Rvalue::BinaryOp(BinOp::Eq, Box::new((Operand::Copy(addr), zero))),
104 ))),
105 ));
106
107 let should_throw_exception =
110 local_decls.push(LocalDecl::with_source_info(tcx.types.bool, source_info)).into();
111 stmts.push(Statement::new(
112 source_info,
113 StatementKind::Assign(Box::new((
114 should_throw_exception,
115 Rvalue::BinaryOp(
116 BinOp::BitAnd,
117 Box::new((Operand::Copy(is_null), pointee_should_be_checked)),
118 ),
119 ))),
120 ));
121
122 let is_ok = local_decls.push(LocalDecl::with_source_info(tcx.types.bool, source_info)).into();
124 stmts.push(Statement::new(
125 source_info,
126 StatementKind::Assign(Box::new((
127 is_ok,
128 Rvalue::UnaryOp(UnOp::Not, Operand::Copy(should_throw_exception)),
129 ))),
130 ));
131
132 PointerCheck {
135 cond: Operand::Copy(is_ok),
136 assert_kind: Box::new(AssertKind::NullPointerDereference),
137 }
138}