compiler/rustc_mir_transform/src/check_packed_ref.rs

   1 use rustc_hir::def_id::{DefId, 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 use rustc_span::symbol::sym;
   8
   9 use crate::util;
  10 use crate::MirLint;
  11
  12 pub(crate) fn provide(providers: &mut Providers) {
  13     *providers = Providers { unsafe_derive_on_repr_packed, ..*providers };
  14 }
  15
  16 pub struct CheckPackedRef;
  17
  18 impl<'tcx> MirLint<'tcx> for CheckPackedRef {
  19     fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
  20         let param_env = tcx.param_env(body.source.def_id());
  21         let source_info = SourceInfo::outermost(body.span);
  22         let mut checker = PackedRefChecker { body, tcx, param_env, source_info };
  23         checker.visit_body(&body);
  24     }
  25 }
  26
  27 struct PackedRefChecker<'a, 'tcx> {
  28     body: &'a Body<'tcx>,
  29     tcx: TyCtxt<'tcx>,
  30     param_env: ty::ParamEnv<'tcx>,
  31     source_info: SourceInfo,
  32 }
  33
  34 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
  35     let lint_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
  36
  37     tcx.struct_span_lint_hir(UNALIGNED_REFERENCES, lint_hir_id, tcx.def_span(def_id), |lint| {
  38         // FIXME: when we make this a hard error, this should have its
  39         // own error code.
  40         let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
  41             "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
  42              type or const parameters (error E0133)"
  43                 .to_string()
  44         } else {
  45             "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
  46              does not derive Copy (error E0133)"
  47                 .to_string()
  48         };
  49         lint.build(&message).emit()
  50     });
  51 }
  52
  53 fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
  54     debug!("builtin_derive_def_id({:?})", def_id);
  55     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
  56         if tcx.has_attr(impl_def_id, sym::automatically_derived) {
  57             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
  58             Some(impl_def_id)
  59         } else {
  60             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
  61             None
  62         }
  63     } else {
  64         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
  65         None
  66     }
  67 }
  68
  69 impl<'tcx> Visitor<'tcx> for PackedRefChecker<'_, 'tcx> {
  70     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  71         // Make sure we know where in the MIR we are.
  72         self.source_info = terminator.source_info;
  73         self.super_terminator(terminator, location);
  74     }
  75
  76     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  77         // Make sure we know where in the MIR we are.
  78         self.source_info = statement.source_info;
  79         self.super_statement(statement, location);
  80     }
  81
  82     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
  83         if context.is_borrow() {
  84             if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
  85                 let def_id = self.body.source.instance.def_id();
  86                 if let Some(impl_def_id) = builtin_derive_def_id(self.tcx, def_id) {
  87                     // If a method is defined in the local crate,
  88                     // the impl containing that method should also be.
  89                     self.tcx.ensure().unsafe_derive_on_repr_packed(impl_def_id.expect_local());
  90                 } else {
  91                     let source_info = self.source_info;
  92                     let lint_root = self.body.source_scopes[source_info.scope]
  93                         .local_data
  94                         .as_ref()
  95                         .assert_crate_local()
  96                         .lint_root;
  97                     self.tcx.struct_span_lint_hir(
  98                         UNALIGNED_REFERENCES,
  99                         lint_root,
 100                         source_info.span,
 101                         |lint| {
 102                             lint.build("reference to packed field is unaligned")
 103                                 .note(
 104                                     "fields of packed structs are not properly aligned, and creating \
 105                                     a misaligned reference is undefined behavior (even if that \
 106                                     reference is never dereferenced)",
 107                                 )
 108                                 .help(
 109                                     "copy the field contents to a local variable, or replace the \
 110                                     reference with a raw pointer and use `read_unaligned`/`write_unaligned` \
 111                                     (loads and stores via `*p` must be properly aligned even when using raw pointers)"
 112                                 )
 113                                 .emit()
 114                         },
 115                     );
 116                 }
 117             }
 118         }
 119     }
 120 }