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     tcx.struct_span_lint_hir(UNALIGNED_REFERENCES, lint_hir_id, tcx.def_span(def_id), |lint| {
  37         // FIXME: when we make this a hard error, this should have its
  38         // own error code.
  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         lint.build(message).emit();
  50     });
  51 }
  52
  53 impl<'tcx> Visitor<'tcx> for PackedRefChecker<'_, 'tcx> {
  54     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  55         // Make sure we know where in the MIR we are.
  56         self.source_info = terminator.source_info;
  57         self.super_terminator(terminator, location);
  58     }
  59
  60     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  61         // Make sure we know where in the MIR we are.
  62         self.source_info = statement.source_info;
  63         self.super_statement(statement, location);
  64     }
  65
  66     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
  67         if context.is_borrow() {
  68             if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
  69                 let def_id = self.body.source.instance.def_id();
  70                 if let Some(impl_def_id) = self
  71                     .tcx
  72                     .impl_of_method(def_id)
  73                     .filter(|&def_id| self.tcx.is_builtin_derive(def_id))
  74                 {
  75                     // If a method is defined in the local crate,
  76                     // the impl containing that method should also be.
  77                     self.tcx.ensure().unsafe_derive_on_repr_packed(impl_def_id.expect_local());
  78                 } else {
  79                     let source_info = self.source_info;
  80                     let lint_root = self.body.source_scopes[source_info.scope]
  81                         .local_data
  82                         .as_ref()
  83                         .assert_crate_local()
  84                         .lint_root;
  85                     self.tcx.struct_span_lint_hir(
  86                         UNALIGNED_REFERENCES,
  87                         lint_root,
  88                         source_info.span,
  89                         |lint| {
  90                             lint.build("reference to packed field is unaligned")
  91                                 .note(
  92                                     "fields of packed structs are not properly aligned, and creating \
  93                                     a misaligned reference is undefined behavior (even if that \
  94                                     reference is never dereferenced)",
  95                                 )
  96                                 .help(
  97                                     "copy the field contents to a local variable, or replace the \
  98                                     reference with a raw pointer and use `read_unaligned`/`write_unaligned` \
  99                                     (loads and stores via `*p` must be properly aligned even when using raw pointers)"
 100                                 )
 101                                 .emit();
 102                         },
 103                     );
 104                 }
 105             }
 106         }
 107     }
 108 }