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 message = if tcx.generics_of(def_id).own_requires_monomorphization() {
  40             "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
  41              type or const parameters (error E0133)"
  42                 .to_string()
  43         } else {
  44             "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
  45              does not derive Copy (error E0133)"
  46                 .to_string()
  47         };
  48         lint.build(&message).emit();
  49     });
  50 }
  51
  52 impl<'tcx> Visitor<'tcx> for PackedRefChecker<'_, 'tcx> {
  53     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  54         // Make sure we know where in the MIR we are.
  55         self.source_info = terminator.source_info;
  56         self.super_terminator(terminator, location);
  57     }
  58
  59     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  60         // Make sure we know where in the MIR we are.
  61         self.source_info = statement.source_info;
  62         self.super_statement(statement, location);
  63     }
  64
  65     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
  66         if context.is_borrow() {
  67             if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
  68                 let def_id = self.body.source.instance.def_id();
  69                 if let Some(impl_def_id) = self
  70                     .tcx
  71                     .impl_of_method(def_id)
  72                     .filter(|&def_id| self.tcx.is_builtin_derive(def_id))
  73                 {
  74                     // If a method is defined in the local crate,
  75                     // the impl containing that method should also be.
  76                     self.tcx.ensure().unsafe_derive_on_repr_packed(impl_def_id.expect_local());
  77                 } else {
  78                     let source_info = self.source_info;
  79                     let lint_root = self.body.source_scopes[source_info.scope]
  80                         .local_data
  81                         .as_ref()
  82                         .assert_crate_local()
  83                         .lint_root;
  84                     self.tcx.struct_span_lint_hir(
  85                         UNALIGNED_REFERENCES,
  86                         lint_root,
  87                         source_info.span,
  88                         |lint| {
  89                             lint.build("reference to packed field is unaligned")
  90                                 .note(
  91                                     "fields of packed structs are not properly aligned, and creating \
  92                                     a misaligned reference is undefined behavior (even if that \
  93                                     reference is never dereferenced)",
  94                                 )
  95                                 .help(
  96                                     "copy the field contents to a local variable, or replace the \
  97                                     reference with a raw pointer and use `read_unaligned`/`write_unaligned` \
  98                                     (loads and stores via `*p` must be properly aligned even when using raw pointers)"
  99                                 )
 100                                 .emit();
 101                         },
 102                     );
 103                 }
 104             }
 105         }
 106     }
 107 }