1 use crate::consts::{constant_context, Constant};
2 use crate::utils::{match_qpath, paths, span_lint};
3 use if_chain::if_chain;
4 use rustc_ast::LitKind;
5 use rustc_hir::{Expr, ExprKind};
6 use rustc_lint::{LateContext, LateLintPass, LintContext};
7 use rustc_middle::lint::in_external_macro;
8 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 declare_clippy_lint! {
11 /// **What it does:** Checks for transmute calls which would receive a null pointer.
13 /// **Why is this bad?** Transmuting a null pointer is undefined behavior.
15 /// **Known problems:** Not all cases can be detected at the moment of this writing.
16 /// For example, variables which hold a null pointer and are then fed to a `transmute`
17 /// call, aren't detectable yet.
21 /// let null_ref: &u64 = unsafe { std::mem::transmute(0 as *const u64) };
25 "transmutes from a null pointer to a reference, which is undefined behavior"
28 declare_lint_pass!(TransmutingNull => [TRANSMUTING_NULL]);
30 const LINT_MSG: &str = "transmuting a known null pointer into a reference.";
32 impl<'tcx> LateLintPass<'tcx> for TransmutingNull {
33 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
34 if in_external_macro(cx.sess(), expr.span) {
39 if let ExprKind::Call(ref func, ref args) = expr.kind;
40 if let ExprKind::Path(ref path) = func.kind;
41 if match_qpath(path, &paths::STD_MEM_TRANSMUTE);
46 // Catching transmute over constants that resolve to `null`.
47 let mut const_eval_context = constant_context(cx, cx.typeck_results());
49 if let ExprKind::Path(ref _qpath) = args[0].kind;
50 let x = const_eval_context.expr(&args[0]);
51 if let Some(Constant::RawPtr(0)) = x;
53 span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG)
58 // `std::mem::transmute(0 as *const i32)`
60 if let ExprKind::Cast(ref inner_expr, ref _cast_ty) = args[0].kind;
61 if let ExprKind::Lit(ref lit) = inner_expr.kind;
62 if let LitKind::Int(0, _) = lit.node;
64 span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG)
69 // `std::mem::transmute(std::ptr::null::<i32>())`
71 if let ExprKind::Call(ref func1, ref args1) = args[0].kind;
72 if let ExprKind::Path(ref path1) = func1.kind;
73 if match_qpath(path1, &paths::STD_PTR_NULL);
76 span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG)
81 // Also catch transmutations of variables which are known nulls.
82 // To do this, MIR const propagation seems to be the better tool.
83 // Whenever MIR const prop routines are more developed, this will
84 // become available. As of this writing (25/03/19) it is not yet.