compiler/rustc_mir_transform/src/check_packed_ref.rs

   1 use rustc_middle::mir::visit::{PlaceContext, Visitor};
   2 use rustc_middle::mir::*;
   3 use rustc_middle::ty::{self, TyCtxt};
   4 use rustc_session::lint::builtin::UNALIGNED_REFERENCES;
   5
   6 use crate::util;
   7 use crate::MirLint;
   8
   9 pub struct CheckPackedRef;
  10
  11 impl<'tcx> MirLint<'tcx> for CheckPackedRef {
  12     fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
  13         let param_env = tcx.param_env(body.source.def_id());
  14         let source_info = SourceInfo::outermost(body.span);
  15         let mut checker = PackedRefChecker { body, tcx, param_env, source_info };
  16         checker.visit_body(&body);
  17     }
  18 }
  19
  20 struct PackedRefChecker<'a, 'tcx> {
  21     body: &'a Body<'tcx>,
  22     tcx: TyCtxt<'tcx>,
  23     param_env: ty::ParamEnv<'tcx>,
  24     source_info: SourceInfo,
  25 }
  26
  27 impl<'tcx> Visitor<'tcx> for PackedRefChecker<'_, 'tcx> {
  28     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  29         // Make sure we know where in the MIR we are.
  30         self.source_info = terminator.source_info;
  31         self.super_terminator(terminator, location);
  32     }
  33
  34     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  35         // Make sure we know where in the MIR we are.
  36         self.source_info = statement.source_info;
  37         self.super_statement(statement, location);
  38     }
  39
  40     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
  41         if context.is_borrow() {
  42             if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
  43                 let def_id = self.body.source.instance.def_id();
  44                 if let Some(impl_def_id) = self.tcx.impl_of_method(def_id)
  45                     && self.tcx.is_builtin_derive(impl_def_id)
  46                 {
  47                     // If we ever reach here it means that the generated derive
  48                     // code is somehow doing an unaligned reference, which it
  49                     // shouldn't do.
  50                     unreachable!();
  51                 } else {
  52                     let source_info = self.source_info;
  53                     let lint_root = self.body.source_scopes[source_info.scope]
  54                         .local_data
  55                         .as_ref()
  56                         .assert_crate_local()
  57                         .lint_root;
  58                     self.tcx.struct_span_lint_hir(
  59                         UNALIGNED_REFERENCES,
  60                         lint_root,
  61                         source_info.span,
  62                         "reference to packed field is unaligned",
  63                         |lint| {
  64                             lint
  65                                 .note(
  66                                     "fields of packed structs are not properly aligned, and creating \
  67                                     a misaligned reference is undefined behavior (even if that \
  68                                     reference is never dereferenced)",
  69                                 )
  70                                 .help(
  71                                     "copy the field contents to a local variable, or replace the \
  72                                     reference with a raw pointer and use `read_unaligned`/`write_unaligned` \
  73                                     (loads and stores via `*p` must be properly aligned even when using raw pointers)"
  74                                 )
  75                         },
  76                     );
  77                 }
  78             }
  79         }
  80     }
  81 }