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 rustc_ast::Mutability;
17 use rustc_middle::{mir, ty};
18 use rustc_span::Symbol;
19 use rustc_target::spec::abi::Abi;
20 use rustc_target::spec::PanicStrategy;
23 use helpers::check_arg_count;
25 /// Holds all of the relevant data for when unwinding hits a `try` frame.
27 pub struct CatchUnwindData<'tcx> {
28 /// The `catch_fn` callback to call in case of a panic.
29 catch_fn: Scalar<Tag>,
30 /// The `data` argument for that callback.
32 /// The return place from the original call to `try`.
33 dest: PlaceTy<'tcx, Tag>,
34 /// The return block from the original call to `try`.
38 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
39 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
40 /// Handles the special `miri_start_panic` intrinsic, which is called
41 /// by libpanic_unwind to delegate the actual unwinding process to Miri.
42 fn handle_miri_start_panic(
46 args: &[OpTy<'tcx, Tag>],
47 unwind: StackPopUnwind,
48 ) -> InterpResult<'tcx> {
49 let this = self.eval_context_mut();
51 trace!("miri_start_panic: {:?}", this.frame().instance);
53 // Get the raw pointer stored in arg[0] (the panic payload).
54 let [payload] = this.check_shim(abi, Abi::Rust, link_name, args)?;
55 let payload = this.read_scalar(payload)?.check_init()?;
56 let thread = this.active_thread_mut();
57 assert!(thread.panic_payload.is_none(), "the panic runtime should avoid double-panics");
58 thread.panic_payload = Some(payload);
60 // Jump to the unwind block to begin unwinding.
61 this.unwind_to_block(unwind)?;
65 /// Handles the `try` intrinsic, the underlying implementation of `std::panicking::try`.
68 args: &[OpTy<'tcx, Tag>],
69 dest: &PlaceTy<'tcx, Tag>,
71 ) -> InterpResult<'tcx> {
72 let this = self.eval_context_mut();
75 // fn r#try(try_fn: fn(*mut u8), data: *mut u8, catch_fn: fn(*mut u8, *mut u8)) -> i32
76 // Calls `try_fn` with `data` as argument. If that executes normally, returns 0.
77 // If that unwinds, calls `catch_fn` with the first argument being `data` and
78 // then second argument being a target-dependent `payload` (i.e. it is up to us to define
79 // what that is), and returns 1.
80 // The `payload` is passed (by libstd) to `__rust_panic_cleanup`, which is then expected to
81 // return a `Box<dyn Any + Send + 'static>`.
82 // In Miri, `miri_start_panic` is passed exactly that type, so we make the `payload` simply
83 // a pointer to `Box<dyn Any + Send + 'static>`.
85 // Get all the arguments.
86 let [try_fn, data, catch_fn] = check_arg_count(args)?;
87 let try_fn = this.read_pointer(try_fn)?;
88 let data = this.read_scalar(data)?.check_init()?;
89 let catch_fn = this.read_scalar(catch_fn)?.check_init()?;
91 // Now we make a function call, and pass `data` as first and only argument.
92 let f_instance = this.get_ptr_fn(try_fn)?.as_instance()?;
93 trace!("try_fn: {:?}", f_instance);
94 let ret_place = MPlaceTy::dangling(this.machine.layouts.unit).into();
100 // Directly return to caller.
101 StackPopCleanup::Goto { ret: Some(ret), unwind: StackPopUnwind::Skip },
104 // We ourselves will return `0`, eventually (will be overwritten if we catch a panic).
105 this.write_null(dest)?;
107 // In unwind mode, we tag this frame with the extra data needed to catch unwinding.
108 // This lets `handle_stack_pop` (below) know that we should stop unwinding
109 // when we pop this frame.
110 if this.tcx.sess.panic_strategy() == PanicStrategy::Unwind {
111 this.frame_mut().extra.catch_unwind =
112 Some(CatchUnwindData { catch_fn, data, dest: *dest, ret });
120 mut extra: FrameData<'tcx>,
122 ) -> InterpResult<'tcx, StackPopJump> {
123 let this = self.eval_context_mut();
125 trace!("handle_stack_pop(extra = {:?}, unwinding = {})", extra, unwinding);
126 if let Some(stacked_borrows) = &this.machine.stacked_borrows {
127 stacked_borrows.borrow_mut().end_call(extra.call_id);
130 // We only care about `catch_panic` if we're unwinding - if we're doing a normal
131 // return, then we don't need to do anything special.
132 if let (true, Some(catch_unwind)) = (unwinding, extra.catch_unwind.take()) {
133 // We've just popped a frame that was pushed by `try`,
134 // and we are unwinding, so we should catch that.
136 "unwinding: found catch_panic frame during unwinding: {:?}",
137 this.frame().instance
140 // We set the return value of `try` to 1, since there was a panic.
141 this.write_scalar(Scalar::from_i32(1), &catch_unwind.dest)?;
143 // The Thread's `panic_payload` holds what was passed to `miri_start_panic`.
144 // This is exactly the second argument we need to pass to `catch_fn`.
145 let payload = this.active_thread_mut().panic_payload.take().unwrap();
147 // Push the `catch_fn` stackframe.
149 this.get_ptr_fn(this.scalar_to_ptr(catch_unwind.catch_fn)?)?.as_instance()?;
150 trace!("catch_fn: {:?}", f_instance);
151 let ret_place = MPlaceTy::dangling(this.machine.layouts.unit).into();
155 &[catch_unwind.data.into(), payload.into()],
157 // Directly return to caller of `try`.
158 StackPopCleanup::Goto { ret: Some(catch_unwind.ret), unwind: StackPopUnwind::Skip },
161 // We pushed a new stack frame, the engine should not do any jumping now!
162 Ok(StackPopJump::NoJump)
164 Ok(StackPopJump::Normal)
168 /// Start a panic in the interpreter with the given message as payload.
169 fn start_panic(&mut self, msg: &str, unwind: StackPopUnwind) -> InterpResult<'tcx> {
170 let this = self.eval_context_mut();
172 // First arg: message.
173 let msg = this.allocate_str(msg, MiriMemoryKind::Machine.into(), Mutability::Not);
175 // Call the lang item.
176 let panic = this.tcx.lang_items().panic_fn().unwrap();
177 let panic = ty::Instance::mono(this.tcx.tcx, panic);
182 &MPlaceTy::dangling(this.machine.layouts.unit).into(),
183 StackPopCleanup::Goto { ret: None, unwind },
189 msg: &mir::AssertMessage<'tcx>,
190 unwind: Option<mir::BasicBlock>,
191 ) -> InterpResult<'tcx> {
192 use rustc_middle::mir::AssertKind::*;
193 let this = self.eval_context_mut();
196 BoundsCheck { index, len } => {
197 // Forward to `panic_bounds_check` lang item.
200 let index = this.read_scalar(&this.eval_operand(index, None)?)?;
202 let len = this.read_scalar(&this.eval_operand(len, None)?)?;
204 // Call the lang item.
205 let panic_bounds_check = this.tcx.lang_items().panic_bounds_check_fn().unwrap();
206 let panic_bounds_check = ty::Instance::mono(this.tcx.tcx, panic_bounds_check);
210 &[index.into(), len.into()],
211 &MPlaceTy::dangling(this.machine.layouts.unit).into(),
212 StackPopCleanup::Goto {
214 unwind: match unwind {
215 Some(cleanup) => StackPopUnwind::Cleanup(cleanup),
216 None => StackPopUnwind::Skip,
222 // Forward everything else to `panic` lang item.
226 Some(cleanup) => StackPopUnwind::Cleanup(cleanup),
227 None => StackPopUnwind::Skip,