| //! Panic runtime for Miri. |
| //! |
| //! The core pieces of the runtime are: |
| //! - An implementation of `__rust_maybe_catch_panic` that pushes the invoked stack frame with |
| //! some extra metadata derived from the panic-catching arguments of `__rust_maybe_catch_panic`. |
| //! - A hack in `libpanic_unwind` that calls the `miri_start_panic` intrinsic instead of the |
| //! target-native panic runtime. (This lives in the rustc repo.) |
| //! - An implementation of `miri_start_panic` that stores its argument (the panic payload), and then |
| //! immediately returns, but on the *unwind* edge (not the normal return edge), thus initiating unwinding. |
| //! - A hook executed each time a frame is popped, such that if the frame pushed by `__rust_maybe_catch_panic` |
| //! gets popped *during unwinding*, we take the panic payload and store it according to the extra |
| //! metadata we remembered when pushing said frame. |
| |
| use rustc::mir; |
| use rustc::ty::{self, layout::LayoutOf}; |
| use rustc_target::spec::PanicStrategy; |
| use rustc_span::source_map::Span; |
| |
| use crate::*; |
| |
| /// Holds all of the relevant data for a call to |
| /// `__rust_maybe_catch_panic`. |
| /// |
| /// If a panic occurs, we update this data with |
| /// the information from the panic site. |
| #[derive(Debug)] |
| pub struct CatchUnwindData<'tcx> { |
| /// The dereferenced `data_ptr` argument passed to `__rust_maybe_catch_panic`. |
| pub data_place: MPlaceTy<'tcx, Tag>, |
| /// The dereferenced `vtable_ptr` argument passed to `__rust_maybe_catch_panic`. |
| pub vtable_place: MPlaceTy<'tcx, Tag>, |
| /// The `dest` from the original call to `__rust_maybe_catch_panic`. |
| pub dest: PlaceTy<'tcx, Tag>, |
| } |
| |
| impl<'mir, 'tcx> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {} |
| pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> { |
| /// Handles the special "miri_start_panic" intrinsic, which is called |
| /// by libpanic_unwind to delegate the actual unwinding process to Miri. |
| fn handle_miri_start_panic( |
| &mut self, |
| args: &[OpTy<'tcx, Tag>], |
| unwind: Option<mir::BasicBlock>, |
| ) -> InterpResult<'tcx> { |
| let this = self.eval_context_mut(); |
| |
| trace!("miri_start_panic: {:?}", this.frame().span); |
| |
| // Get the raw pointer stored in arg[0] (the panic payload). |
| let scalar = this.read_immediate(args[0])?; |
| assert!( |
| this.machine.panic_payload.is_none(), |
| "the panic runtime should avoid double-panics" |
| ); |
| this.machine.panic_payload = Some(scalar); |
| |
| // Jump to the unwind block to begin unwinding. |
| this.unwind_to_block(unwind); |
| return Ok(()); |
| } |
| |
| fn handle_catch_panic( |
| &mut self, |
| args: &[OpTy<'tcx, Tag>], |
| dest: PlaceTy<'tcx, Tag>, |
| ret: mir::BasicBlock, |
| ) -> InterpResult<'tcx> { |
| let this = self.eval_context_mut(); |
| let tcx = &{ this.tcx.tcx }; |
| |
| // fn __rust_maybe_catch_panic( |
| // f: fn(*mut u8), |
| // data: *mut u8, |
| // data_ptr: *mut usize, |
| // vtable_ptr: *mut usize, |
| // ) -> u32 |
| |
| // Get all the arguments. |
| let f = this.read_scalar(args[0])?.not_undef()?; |
| let f_arg = this.read_scalar(args[1])?.not_undef()?; |
| let data_place = this.deref_operand(args[2])?; |
| let vtable_place = this.deref_operand(args[3])?; |
| |
| // Now we make a function call, and pass `f_arg` as first and only argument. |
| let f_instance = this.memory.get_fn(f)?.as_instance()?; |
| trace!("__rust_maybe_catch_panic: {:?}", f_instance); |
| let ret_place = MPlaceTy::dangling(this.layout_of(tcx.mk_unit())?, this).into(); |
| this.call_function( |
| f_instance, |
| &[f_arg.into()], |
| Some(ret_place), |
| // Directly return to caller. |
| StackPopCleanup::Goto { ret: Some(ret), unwind: None }, |
| )?; |
| |
| // We ourselves will return `0`, eventually (will be overwritten if we catch a panic). |
| this.write_null(dest)?; |
| |
| // In unwind mode, we tag this frame with some extra data. |
| // This lets `handle_stack_pop` (below) know that we should stop unwinding |
| // when we pop this frame. |
| if this.tcx.tcx.sess.panic_strategy() == PanicStrategy::Unwind { |
| this.frame_mut().extra.catch_panic = |
| Some(CatchUnwindData { data_place, vtable_place, dest }) |
| } |
| |
| return Ok(()); |
| } |
| |
| fn handle_stack_pop( |
| &mut self, |
| mut extra: FrameData<'tcx>, |
| unwinding: bool, |
| ) -> InterpResult<'tcx, StackPopInfo> { |
| let this = self.eval_context_mut(); |
| |
| trace!("handle_stack_pop(extra = {:?}, unwinding = {})", extra, unwinding); |
| |
| // We only care about `catch_panic` if we're unwinding - if we're doing a normal |
| // return, then we don't need to do anything special. |
| let res = if let (true, Some(unwind_data)) = (unwinding, extra.catch_panic.take()) { |
| // We've just popped a frame that was pushed by `__rust_maybe_catch_panic`, |
| // and we are unwinding, so we should catch that. |
| trace!("unwinding: found catch_panic frame during unwinding: {:?}", this.frame().span); |
| |
| // `panic_payload` now holds a `*mut (dyn Any + Send)`, |
| // provided by the `miri_start_panic` intrinsic. |
| // We want to split this into its consituient parts - |
| // the data and vtable pointers - and store them according to |
| // `unwind_data`, i.e., we store them where `__rust_maybe_catch_panic` |
| // was told to put them. |
| let payload = this.machine.panic_payload.take().unwrap(); |
| let payload = this.ref_to_mplace(payload)?; |
| let payload_data_place = payload.ptr; |
| let payload_vtable_place = payload.meta.unwrap_meta(); |
| |
| this.write_scalar(payload_data_place, unwind_data.data_place.into())?; |
| this.write_scalar(payload_vtable_place, unwind_data.vtable_place.into())?; |
| |
| // We set the return value of `__rust_maybe_catch_panic` to 1, |
| // since there was a panic. |
| let dest = unwind_data.dest; |
| this.write_scalar(Scalar::from_int(1, dest.layout.size), dest)?; |
| |
| StackPopInfo::StopUnwinding |
| } else { |
| StackPopInfo::Normal |
| }; |
| if let Some(stacked_borrows) = this.memory.extra.stacked_borrows.as_ref() { |
| stacked_borrows.borrow_mut().end_call(extra.call_id); |
| } |
| Ok(res) |
| } |
| |
| fn assert_panic( |
| &mut self, |
| span: Span, |
| msg: &mir::AssertMessage<'tcx>, |
| unwind: Option<mir::BasicBlock>, |
| ) -> InterpResult<'tcx> { |
| use rustc::mir::AssertKind::*; |
| let this = self.eval_context_mut(); |
| |
| match msg { |
| BoundsCheck { ref index, ref len } => { |
| // Forward to `panic_bounds_check` lang item. |
| |
| // First arg: Caller location. |
| let location = this.alloc_caller_location_for_span(span); |
| // Second arg: index. |
| let index = this.read_scalar(this.eval_operand(index, None)?)?; |
| // Third arg: len. |
| let len = this.read_scalar(this.eval_operand(len, None)?)?; |
| |
| // Call the lang item. |
| let panic_bounds_check = this.tcx.lang_items().panic_bounds_check_fn().unwrap(); |
| let panic_bounds_check = ty::Instance::mono(this.tcx.tcx, panic_bounds_check); |
| this.call_function( |
| panic_bounds_check, |
| &[location.ptr.into(), index.into(), len.into()], |
| None, |
| StackPopCleanup::Goto { ret: None, unwind }, |
| )?; |
| } |
| _ => { |
| // Forward everything else to `panic` lang item. |
| |
| // First arg: Message. |
| let msg = msg.description(); |
| let msg = this.allocate_str(msg, MiriMemoryKind::Machine.into()); |
| |
| // Call the lang item. |
| let panic = this.tcx.lang_items().panic_fn().unwrap(); |
| let panic = ty::Instance::mono(this.tcx.tcx, panic); |
| this.call_function( |
| panic, |
| &[msg.to_ref()], |
| None, |
| StackPopCleanup::Goto { ret: None, unwind }, |
| )?; |
| } |
| } |
| Ok(()) |
| } |
| } |