1 //! Panic runtime for Miri.
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.
16 use super::machine::FrameData;
17 use rustc_target::spec::PanicStrategy;
18 use crate::rustc_target::abi::LayoutOf;
20 /// Holds all of the relevant data for a call to
21 /// `__rust_maybe_catch_panic`.
23 /// If a panic occurs, we update this data with
24 /// the information from the panic site.
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>,
35 impl<'mir, 'tcx> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
36 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
38 /// Handles the special "miri_start_panic" intrinsic, which is called
39 /// by libpanic_unwind to delegate the actual unwinding process to Miri.
41 fn handle_miri_start_panic(
43 args: &[OpTy<'tcx, Tag>],
44 unwind: Option<mir::BasicBlock>
45 ) -> InterpResult<'tcx> {
46 let this = self.eval_context_mut();
48 trace!("miri_start_panic: {:?}", this.frame().span);
50 if this.tcx.tcx.sess.panic_strategy() == PanicStrategy::Abort {
51 // FIXME: Add a better way of indicating 'abnormal' termination,
52 // since this is not really an 'unsupported' behavior
53 throw_unsup_format!("the evaluated program panicked");
56 // Get the raw pointer stored in arg[0] (the panic payload).
57 let scalar = this.read_immediate(args[0])?;
58 assert!(this.machine.panic_payload.is_none(), "the panic runtime should avoid double-panics");
59 this.machine.panic_payload = Some(scalar);
61 // Jump to the unwind block to begin unwinding.
62 // We don't use `goto_block` as that is just meant for normal returns.
63 let next_frame = this.frame_mut();
64 next_frame.block = unwind;
70 fn handle_catch_panic(
72 args: &[OpTy<'tcx, Tag>],
73 dest: PlaceTy<'tcx, Tag>,
75 ) -> InterpResult<'tcx> {
76 let this = self.eval_context_mut();
77 let tcx = &{this.tcx.tcx};
79 // fn __rust_maybe_catch_panic(
82 // data_ptr: *mut usize,
83 // vtable_ptr: *mut usize,
86 // Get all the arguments.
87 let f = this.read_scalar(args[0])?.not_undef()?;
88 let f_arg = this.read_scalar(args[1])?.not_undef()?;
89 let data_place = this.deref_operand(args[2])?;
90 let vtable_place = this.deref_operand(args[3])?;
92 // Now we make a function call, and pass `f_arg` as first and only argument.
93 let f_instance = this.memory.get_fn(f)?.as_instance()?;
94 trace!("__rust_maybe_catch_panic: {:?}", f_instance);
95 // TODO: consider making this reusable? `InterpCx::step` does something similar
96 // for the TLS destructors, and of course `eval_main`.
97 let mir = this.load_mir(f_instance.def, None)?;
99 MPlaceTy::dangling(this.layout_of(tcx.mk_unit())?, this).into();
100 this.push_stack_frame(
105 // Directly return to caller.
106 StackPopCleanup::Goto { ret: Some(ret), unwind: None },
109 let mut args = this.frame().body.args_iter();
113 .expect("Argument to __rust_maybe_catch_panic does not take enough arguments.");
114 let arg_dest = this.local_place(arg_local)?;
115 this.write_scalar(f_arg, arg_dest)?;
116 // No more arguments.
117 args.next().expect_none("__rust_maybe_catch_panic argument has more arguments than expected");
119 // We ourselves will return `0`, eventually (will be overwritten if we catch a panic).
120 this.write_null(dest)?;
122 // In unwind mode, we tag this frame with some extra data.
123 // This lets `handle_stack_pop` (below) know that we should stop unwinding
124 // when we pop this frame.
125 if this.tcx.tcx.sess.panic_strategy() == PanicStrategy::Unwind {
126 this.frame_mut().extra.catch_panic = Some(CatchUnwindData {
139 mut extra: FrameData<'tcx>,
141 ) -> InterpResult<'tcx, StackPopInfo> {
142 let this = self.eval_context_mut();
144 trace!("handle_stack_pop(extra = {:?}, unwinding = {})", extra, unwinding);
146 // We only care about `catch_panic` if we're unwinding - if we're doing a normal
147 // return, then we don't need to do anything special.
148 let res = if let (true, Some(unwind_data)) = (unwinding, extra.catch_panic.take()) {
149 // We've just popped a frame that was pushed by `__rust_maybe_catch_panic`,
150 // and we are unwinding, so we should catch that.
151 trace!("unwinding: found catch_panic frame during unwinding: {:?}", this.frame().span);
153 // `panic_payload` now holds a `*mut (dyn Any + Send)`,
154 // provided by the `miri_start_panic` intrinsic.
155 // We want to split this into its consituient parts -
156 // the data and vtable pointers - and store them according to
157 // `unwind_data`, i.e., we store them where `__rust_maybe_catch_panic`
158 // was told to put them.
159 let payload = this.machine.panic_payload.take().unwrap();
160 let payload = this.ref_to_mplace(payload)?;
161 let payload_data_place = payload.ptr;
162 let payload_vtable_place = payload.meta.expect("Expected fat pointer");
164 this.write_scalar(payload_data_place, unwind_data.data_place.into())?;
165 this.write_scalar(payload_vtable_place, unwind_data.vtable_place.into())?;
167 // We set the return value of `__rust_maybe_catch_panic` to 1,
168 // since there was a panic.
169 let dest = unwind_data.dest;
170 this.write_scalar(Scalar::from_int(1, dest.layout.size), dest)?;
172 StackPopInfo::StopUnwinding
176 this.memory.extra.stacked_borrows.borrow_mut().end_call(extra.call_id);