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::hir::{Expr, ExprKind};
5 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
6 use rustc::{declare_lint_pass, declare_tool_lint};
7 use syntax::ast::LitKind;
10 /// **What it does:** Checks for transmute calls which would receive a null pointer.
12 /// **Why is this bad?** Transmuting a null pointer is undefined behavior.
14 /// **Known problems:** Not all cases can be detected at the moment of this writing.
15 /// For example, variables which hold a null pointer and are then fed to a `transmute`
16 /// call, aren't detectable yet.
20 /// let null_ref: &u64 = unsafe { std::mem::transmute(0 as *const u64) };
24 "transmutes from a null pointer to a reference, which is undefined behavior"
27 declare_lint_pass!(TransmutingNull => [TRANSMUTING_NULL]);
29 const LINT_MSG: &str = "transmuting a known null pointer into a reference.";
31 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TransmutingNull {
32 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
33 if in_external_macro(cx.sess(), expr.span) {
38 if let ExprKind::Call(ref func, ref args) = expr.kind;
39 if let ExprKind::Path(ref path) = func.kind;
40 if match_qpath(path, &paths::STD_MEM_TRANSMUTE);
45 // Catching transmute over constants that resolve to `null`.
46 let mut const_eval_context = constant_context(cx, cx.tables);
48 if let ExprKind::Path(ref _qpath) = args[0].kind;
49 let x = const_eval_context.expr(&args[0]);
50 if let Some(constant) = x;
51 if let Constant::RawPtr(0) = constant;
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.