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.
15 use rustc::ty::{self, layout::LayoutOf};
16 use rustc_target::spec::PanicStrategy;
20 /// Holds all of the relevant data for when unwinding hits a `try` frame.
22 pub struct CatchUnwindData<'tcx> {
23 /// The `catch_fn` callback to call in case of a panic.
24 catch_fn: Scalar<Tag>,
25 /// The `data` argument for that callback.
27 /// The return place from the original call to `try`.
28 dest: PlaceTy<'tcx, Tag>,
29 /// The return block from the original call to `try`.
33 impl<'mir, 'tcx> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
34 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
35 /// Handles the special `miri_start_panic` intrinsic, which is called
36 /// by libpanic_unwind to delegate the actual unwinding process to Miri.
37 fn handle_miri_start_panic(
39 args: &[OpTy<'tcx, Tag>],
40 unwind: Option<mir::BasicBlock>,
41 ) -> InterpResult<'tcx> {
42 let this = self.eval_context_mut();
44 trace!("miri_start_panic: {:?}", this.frame().span);
46 // Get the raw pointer stored in arg[0] (the panic payload).
47 let payload = this.read_scalar(args[0])?.not_undef()?;
49 this.machine.panic_payload.is_none(),
50 "the panic runtime should avoid double-panics"
52 this.machine.panic_payload = Some(payload);
54 // Jump to the unwind block to begin unwinding.
55 this.unwind_to_block(unwind);
59 /// Handles the `try` intrinsic, the underlying implementation of `std::panicking::try`.
62 args: &[OpTy<'tcx, Tag>],
63 dest: PlaceTy<'tcx, Tag>,
65 ) -> InterpResult<'tcx> {
66 let this = self.eval_context_mut();
69 // fn r#try(try_fn: fn(*mut u8), data: *mut u8, catch_fn: fn(*mut u8, *mut u8)) -> i32
70 // Calls `try_fn` with `data` as argument. If that executes normally, returns 0.
71 // If that unwinds, calls `catch_fn` with the first argument being `data` and
72 // then second argument being a target-dependent `payload` (i.e. it is up to us to define
73 // what that is), and returns 1.
74 // The `payload` is passed (by libstd) to `__rust_panic_cleanup`, which is then expected to
75 // return a `Box<dyn Any + Send + 'static>`.
76 // In Miri, `miri_start_panic` is passed exactly that type, so we make the `payload` simply
77 // a pointer to `Box<dyn Any + Send + 'static>`.
79 // Get all the arguments.
80 let try_fn = this.read_scalar(args[0])?.not_undef()?;
81 let data = this.read_scalar(args[1])?.not_undef()?;
82 let catch_fn = this.read_scalar(args[2])?.not_undef()?;
84 // Now we make a function call, and pass `data` as first and only argument.
85 let f_instance = this.memory.get_fn(try_fn)?.as_instance()?;
86 trace!("try_fn: {:?}", f_instance);
87 let ret_place = MPlaceTy::dangling(this.layout_of(this.tcx.mk_unit())?, this).into();
92 // Directly return to caller.
93 StackPopCleanup::Goto { ret: Some(ret), unwind: None },
96 // We ourselves will return `0`, eventually (will be overwritten if we catch a panic).
97 this.write_null(dest)?;
99 // In unwind mode, we tag this frame with the extra data needed to catch unwinding.
100 // This lets `handle_stack_pop` (below) know that we should stop unwinding
101 // when we pop this frame.
102 if this.tcx.sess.panic_strategy() == PanicStrategy::Unwind {
103 this.frame_mut().extra.catch_unwind = Some(CatchUnwindData { catch_fn, data, dest, ret });
111 mut extra: FrameData<'tcx>,
113 ) -> InterpResult<'tcx, StackPopJump> {
114 let this = self.eval_context_mut();
116 trace!("handle_stack_pop(extra = {:?}, unwinding = {})", extra, unwinding);
117 if let Some(stacked_borrows) = this.memory.extra.stacked_borrows.as_ref() {
118 stacked_borrows.borrow_mut().end_call(extra.call_id);
121 // We only care about `catch_panic` if we're unwinding - if we're doing a normal
122 // return, then we don't need to do anything special.
123 if let (true, Some(catch_unwind)) = (unwinding, extra.catch_unwind.take()) {
124 // We've just popped a frame that was pushed by `try`,
125 // and we are unwinding, so we should catch that.
126 trace!("unwinding: found catch_panic frame during unwinding: {:?}", this.frame().span);
128 // We set the return value of `try` to 1, since there was a panic.
129 this.write_scalar(Scalar::from_i32(1), catch_unwind.dest)?;
131 // `panic_payload` holds what was passed to `miri_start_panic`.
132 // This is exactly the second argument we need to pass to `catch_fn`.
133 let payload = this.machine.panic_payload.take().unwrap();
135 // Push the `catch_fn` stackframe.
136 let f_instance = this.memory.get_fn(catch_unwind.catch_fn)?.as_instance()?;
137 trace!("catch_fn: {:?}", f_instance);
138 let ret_place = MPlaceTy::dangling(this.layout_of(this.tcx.mk_unit())?, this).into();
141 &[catch_unwind.data.into(), payload.into()],
143 // Directly return to caller of `try`.
144 StackPopCleanup::Goto { ret: Some(catch_unwind.ret), unwind: None },
147 // We pushed a new stack frame, the engine should not do any jumping now!
148 Ok(StackPopJump::NoJump)
150 Ok(StackPopJump::Normal)
154 /// Starta a panic in the interpreter with the given message as payload.
158 unwind: Option<mir::BasicBlock>,
159 ) -> InterpResult<'tcx> {
160 let this = self.eval_context_mut();
162 // First arg: message.
163 let msg = this.allocate_str(msg, MiriMemoryKind::Machine.into());
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);
172 StackPopCleanup::Goto { ret: None, unwind },
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();
185 BoundsCheck { ref index, ref len } => {
186 // Forward to `panic_bounds_check` lang item.
189 let index = this.read_scalar(this.eval_operand(index, None)?)?;
191 let len = this.read_scalar(this.eval_operand(len, None)?)?;
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);
198 &[index.into(), len.into()],
200 StackPopCleanup::Goto { ret: None, unwind },
204 // Forward everything else to `panic` lang item.
205 this.start_panic(msg.description(), unwind)?;