compiler/rustc_mir_transform/src/check_packed_ref.rs

   1 use rustc_hir::def_id::LocalDefId;
   2 use rustc_middle::mir::visit::{PlaceContext, Visitor};
   3 use rustc_middle::mir::*;
   4 use rustc_middle::ty::query::Providers;
   5 use rustc_middle::ty::{self, TyCtxt};
   6 use rustc_session::lint::builtin::UNALIGNED_REFERENCES;
   7
   8 use crate::util;
   9 use crate::MirLint;
  10
  11 pub(crate) fn provide(providers: &mut Providers) {
  12     *providers = Providers { unsafe_derive_on_repr_packed, ..*providers };
  13 }
  14
  15 pub struct CheckPackedRef;
  16
  17 impl<'tcx> MirLint<'tcx> for CheckPackedRef {
  18     fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
  19         let param_env = tcx.param_env(body.source.def_id());
  20         let source_info = SourceInfo::outermost(body.span);
  21         let mut checker = PackedRefChecker { body, tcx, param_env, source_info };
  22         checker.visit_body(&body);
  23     }
  24 }
  25
  26 struct PackedRefChecker<'a, 'tcx> {
  27     body: &'a Body<'tcx>,
  28     tcx: TyCtxt<'tcx>,
  29     param_env: ty::ParamEnv<'tcx>,
  30     source_info: SourceInfo,
  31 }
  32
  33 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
  34     let lint_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
  35
  36     // FIXME: when we make this a hard error, this should have its
  37     // own error code.
  38
  39     let extra = if tcx.generics_of(def_id).own_requires_monomorphization() {
  40         "with type or const parameters"
  41     } else {
  42         "that does not derive `Copy`"
  43     };
  44     let message = format!(
  45         "`{}` can't be derived on this `#[repr(packed)]` struct {}",
  46         tcx.item_name(tcx.trait_id_of_impl(def_id.to_def_id()).expect("derived trait name")),
  47         extra
  48     );
  49
  50     tcx.struct_span_lint_hir(
  51         UNALIGNED_REFERENCES,
  52         lint_hir_id,
  53         tcx.def_span(def_id),
  54         message,
  55         |lint| lint,
  56     );
  57 }
  58
  59 impl<'tcx> Visitor<'tcx> for PackedRefChecker<'_, 'tcx> {
  60     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  61         // Make sure we know where in the MIR we are.
  62         self.source_info = terminator.source_info;
  63         self.super_terminator(terminator, location);
  64     }
  65
  66     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  67         // Make sure we know where in the MIR we are.
  68         self.source_info = statement.source_info;
  69         self.super_statement(statement, location);
  70     }
  71
  72     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
  73         if context.is_borrow() {
  74             if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
  75                 let def_id = self.body.source.instance.def_id();
  76                 if let Some(impl_def_id) = self
  77                     .tcx
  78                     .impl_of_method(def_id)
  79                     .filter(|&def_id| self.tcx.is_builtin_derive(def_id))
  80                 {
  81                     // If a method is defined in the local crate,
  82                     // the impl containing that method should also be.
  83                     self.tcx.ensure().unsafe_derive_on_repr_packed(impl_def_id.expect_local());
  84                 } else {
  85                     let source_info = self.source_info;
  86                     let lint_root = self.body.source_scopes[source_info.scope]
  87                         .local_data
  88                         .as_ref()
  89                         .assert_crate_local()
  90                         .lint_root;
  91                     self.tcx.struct_span_lint_hir(
  92                         UNALIGNED_REFERENCES,
  93                         lint_root,
  94                         source_info.span,
  95                         "reference to packed field is unaligned",
  96                         |lint| {
  97                             lint
  98                                 .note(
  99                                     "fields of packed structs are not properly aligned, and creating \
 100                                     a misaligned reference is undefined behavior (even if that \
 101                                     reference is never dereferenced)",
 102                                 )
 103                                 .help(
 104                                     "copy the field contents to a local variable, or replace the \
 105                                     reference with a raw pointer and use `read_unaligned`/`write_unaligned` \
 106                                     (loads and stores via `*p` must be properly aligned even when using raw pointers)"
 107                                 )
 108                         },
 109                     );
 110                 }
 111             }
 112         }
 113     }
 114 }