src/shims/panic.rs

   1 //! Panic runtime for Miri.
   2 //!
   3 //! The core pieces of the runtime are:
   4 //! - An implementation of `__rust_maybe_catch_panic` that pushes the invoked stack frame with
   5 //!   some extra metadata derived from the panic-catching arguments of `__rust_maybe_catch_panic`.
   6 //! - A hack in `libpanic_unwind` that calls the `miri_start_panic` intrinsic instead of the
   7 //!   target-native panic runtime. (This lives in the rustc repo.)
   8 //! - An implementation of `miri_start_panic` that stores its argument (the panic payload), and then
   9 //!   immediately returns, but on the *unwind* edge (not the normal return edge), thus initiating unwinding.
  10 //! - A hook executed each time a frame is popped, such that if the frame pushed by `__rust_maybe_catch_panic`
  11 //!   gets popped *during unwinding*, we take the panic payload and store it according to the extra
  12 //!   metadata we remembered when pushing said frame.
  13
  14 use rustc::mir;
  15 use rustc::ty::{self, layout::LayoutOf};
  16 use rustc_target::spec::PanicStrategy;
  17
  18 use crate::*;
  19
  20 /// Holds all of the relevant data for a call to
  21 /// `__rust_maybe_catch_panic`.
  22 ///
  23 /// If a panic occurs, we update this data with
  24 /// the information from the panic site.
  25 #[derive(Debug)]
  26 pub struct CatchUnwindData<'tcx> {
  27     /// The dereferenced `data_ptr` argument passed to `__rust_maybe_catch_panic`.
  28     pub data_place: MPlaceTy<'tcx, Tag>,
  29     /// The dereferenced `vtable_ptr` argument passed to `__rust_maybe_catch_panic`.
  30     pub vtable_place: MPlaceTy<'tcx, Tag>,
  31     /// The `dest` from the original call to `__rust_maybe_catch_panic`.
  32     pub dest: PlaceTy<'tcx, Tag>,
  33 }
  34
  35 impl<'mir, 'tcx> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
  36 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
  37     /// Handles the special "miri_start_panic" intrinsic, which is called
  38     /// by libpanic_unwind to delegate the actual unwinding process to Miri.
  39     fn handle_miri_start_panic(
  40         &mut self,
  41         args: &[OpTy<'tcx, Tag>],
  42         unwind: Option<mir::BasicBlock>,
  43     ) -> InterpResult<'tcx> {
  44         let this = self.eval_context_mut();
  45
  46         trace!("miri_start_panic: {:?}", this.frame().span);
  47
  48         // Get the raw pointer stored in arg[0] (the panic payload).
  49         let scalar = this.read_immediate(args[0])?;
  50         assert!(
  51             this.machine.panic_payload.is_none(),
  52             "the panic runtime should avoid double-panics"
  53         );
  54         this.machine.panic_payload = Some(scalar);
  55
  56         // Jump to the unwind block to begin unwinding.
  57         this.unwind_to_block(unwind);
  58         return Ok(());
  59     }
  60
  61     fn handle_catch_panic(
  62         &mut self,
  63         args: &[OpTy<'tcx, Tag>],
  64         dest: PlaceTy<'tcx, Tag>,
  65         ret: mir::BasicBlock,
  66     ) -> InterpResult<'tcx> {
  67         let this = self.eval_context_mut();
  68         let tcx = &{ this.tcx.tcx };
  69
  70         // fn __rust_maybe_catch_panic(
  71         //     f: fn(*mut u8),
  72         //     data: *mut u8,
  73         //     data_ptr: *mut usize,
  74         //     vtable_ptr: *mut usize,
  75         // ) -> u32
  76
  77         // Get all the arguments.
  78         let f = this.read_scalar(args[0])?.not_undef()?;
  79         let f_arg = this.read_scalar(args[1])?.not_undef()?;
  80         let data_place = this.deref_operand(args[2])?;
  81         let vtable_place = this.deref_operand(args[3])?;
  82
  83         // Now we make a function call, and pass `f_arg` as first and only argument.
  84         let f_instance = this.memory.get_fn(f)?.as_instance()?;
  85         trace!("__rust_maybe_catch_panic: {:?}", f_instance);
  86         let ret_place = MPlaceTy::dangling(this.layout_of(tcx.mk_unit())?, this).into();
  87         this.call_function(
  88             f_instance,
  89             &[f_arg.into()],
  90             Some(ret_place),
  91             // Directly return to caller.
  92             StackPopCleanup::Goto { ret: Some(ret), unwind: None },
  93         )?;
  94
  95         // We ourselves will return `0`, eventually (will be overwritten if we catch a panic).
  96         this.write_null(dest)?;
  97
  98         // In unwind mode, we tag this frame with some extra data.
  99         // This lets `handle_stack_pop` (below) know that we should stop unwinding
 100         // when we pop this frame.
 101         if this.tcx.tcx.sess.panic_strategy() == PanicStrategy::Unwind {
 102             this.frame_mut().extra.catch_panic =
 103                 Some(CatchUnwindData { data_place, vtable_place, dest })
 104         }
 105
 106         return Ok(());
 107     }
 108
 109     fn handle_stack_pop(
 110         &mut self,
 111         mut extra: FrameData<'tcx>,
 112         unwinding: bool,
 113     ) -> InterpResult<'tcx, StackPopInfo> {
 114         let this = self.eval_context_mut();
 115
 116         trace!("handle_stack_pop(extra = {:?}, unwinding = {})", extra, unwinding);
 117
 118         // We only care about `catch_panic` if we're unwinding - if we're doing a normal
 119         // return, then we don't need to do anything special.
 120         let res = if let (true, Some(unwind_data)) = (unwinding, extra.catch_panic.take()) {
 121             // We've just popped a frame that was pushed by `__rust_maybe_catch_panic`,
 122             // and we are unwinding, so we should catch that.
 123             trace!("unwinding: found catch_panic frame during unwinding: {:?}", this.frame().span);
 124
 125             // `panic_payload` now holds a `*mut (dyn Any + Send)`,
 126             // provided by the `miri_start_panic` intrinsic.
 127             // We want to split this into its consituient parts -
 128             // the data and vtable pointers - and store them according to
 129             // `unwind_data`, i.e., we store them where `__rust_maybe_catch_panic`
 130             // was told to put them.
 131             let payload = this.machine.panic_payload.take().unwrap();
 132             let payload = this.ref_to_mplace(payload)?;
 133             let payload_data_place = payload.ptr;
 134             let payload_vtable_place = payload.meta.unwrap_meta();
 135
 136             this.write_scalar(payload_data_place, unwind_data.data_place.into())?;
 137             this.write_scalar(payload_vtable_place, unwind_data.vtable_place.into())?;
 138
 139             // We set the return value of `__rust_maybe_catch_panic` to 1,
 140             // since there was a panic.
 141             let dest = unwind_data.dest;
 142             this.write_scalar(Scalar::from_int(1, dest.layout.size), dest)?;
 143
 144             StackPopInfo::StopUnwinding
 145         } else {
 146             StackPopInfo::Normal
 147         };
 148         if let Some(stacked_borrows) = this.memory.extra.stacked_borrows.as_ref() {
 149             stacked_borrows.borrow_mut().end_call(extra.call_id);
 150         }
 151         Ok(res)
 152     }
 153
 154     /// Starta a panic in the interpreter with the given message as payload.
 155     fn start_panic(
 156         &mut self,
 157         msg: &str,
 158         unwind: Option<mir::BasicBlock>,
 159     ) -> InterpResult<'tcx> {
 160         let this = self.eval_context_mut();
 161
 162         // First arg: message.
 163         let msg = this.allocate_str(msg, MiriMemoryKind::Machine.into());
 164
 165         // Call the lang item.
 166         let panic = this.tcx.lang_items().panic_fn().unwrap();
 167         let panic = ty::Instance::mono(this.tcx.tcx, panic);
 168         this.call_function(
 169             panic,
 170             &[msg.to_ref()],
 171             None,
 172             StackPopCleanup::Goto { ret: None, unwind },
 173         )
 174     }
 175
 176     fn assert_panic(
 177         &mut self,
 178         msg: &mir::AssertMessage<'tcx>,
 179         unwind: Option<mir::BasicBlock>,
 180     ) -> InterpResult<'tcx> {
 181         use rustc::mir::AssertKind::*;
 182         let this = self.eval_context_mut();
 183
 184         match msg {
 185             BoundsCheck { ref index, ref len } => {
 186                 // Forward to `panic_bounds_check` lang item.
 187
 188                 // First arg: index.
 189                 let index = this.read_scalar(this.eval_operand(index, None)?)?;
 190                 // Second arg: len.
 191                 let len = this.read_scalar(this.eval_operand(len, None)?)?;
 192
 193                 // Call the lang item.
 194                 let panic_bounds_check = this.tcx.lang_items().panic_bounds_check_fn().unwrap();
 195                 let panic_bounds_check = ty::Instance::mono(this.tcx.tcx, panic_bounds_check);
 196                 this.call_function(
 197                     panic_bounds_check,
 198                     &[index.into(), len.into()],
 199                     None,
 200                     StackPopCleanup::Goto { ret: None, unwind },
 201                 )?;
 202             }
 203             _ => {
 204                 // Forward everything else to `panic` lang item.
 205                 this.start_panic(msg.description(), unwind)?;
 206             }
 207         }
 208         Ok(())
 209     }
 210 }