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_middle::{mir, ty};
17 use rustc_target::spec::PanicStrategy;
20 use helpers::check_arg_count;
22 /// Holds all of the relevant data for when unwinding hits a `try` frame.
24 pub struct CatchUnwindData<'tcx> {
25 /// The `catch_fn` callback to call in case of a panic.
26 catch_fn: Scalar<Tag>,
27 /// The `data` argument for that callback.
29 /// The return place from the original call to `try`.
30 dest: PlaceTy<'tcx, Tag>,
31 /// The return block from the original call to `try`.
35 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
36 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
37 /// Check if panicking is supported on this target, and give a good error otherwise.
38 fn check_panic_supported(&self) -> InterpResult<'tcx> {
39 match self.eval_context_ref().tcx.sess.target.target.target_os.as_str() {
40 "linux" | "macos" => Ok(()),
41 _ => throw_unsup_format!("panicking is not supported on this target"),
45 /// Handles the special `miri_start_panic` intrinsic, which is called
46 /// by libpanic_unwind to delegate the actual unwinding process to Miri.
47 fn handle_miri_start_panic(
49 args: &[OpTy<'tcx, Tag>],
50 unwind: Option<mir::BasicBlock>,
51 ) -> InterpResult<'tcx> {
52 let this = self.eval_context_mut();
54 trace!("miri_start_panic: {:?}", this.frame().instance);
56 // Get the raw pointer stored in arg[0] (the panic payload).
57 let &[payload] = check_arg_count(args)?;
58 let payload = this.read_scalar(payload)?.not_undef()?;
60 this.machine.panic_payload.is_none(),
61 "the panic runtime should avoid double-panics"
63 this.machine.panic_payload = Some(payload);
65 // Jump to the unwind block to begin unwinding.
66 this.unwind_to_block(unwind);
70 /// Handles the `try` intrinsic, the underlying implementation of `std::panicking::try`.
73 args: &[OpTy<'tcx, Tag>],
74 dest: PlaceTy<'tcx, Tag>,
76 ) -> InterpResult<'tcx> {
77 let this = self.eval_context_mut();
80 // fn r#try(try_fn: fn(*mut u8), data: *mut u8, catch_fn: fn(*mut u8, *mut u8)) -> i32
81 // Calls `try_fn` with `data` as argument. If that executes normally, returns 0.
82 // If that unwinds, calls `catch_fn` with the first argument being `data` and
83 // then second argument being a target-dependent `payload` (i.e. it is up to us to define
84 // what that is), and returns 1.
85 // The `payload` is passed (by libstd) to `__rust_panic_cleanup`, which is then expected to
86 // return a `Box<dyn Any + Send + 'static>`.
87 // In Miri, `miri_start_panic` is passed exactly that type, so we make the `payload` simply
88 // a pointer to `Box<dyn Any + Send + 'static>`.
90 // Get all the arguments.
91 let &[try_fn, data, catch_fn] = check_arg_count(args)?;
92 let try_fn = this.read_scalar(try_fn)?.not_undef()?;
93 let data = this.read_scalar(data)?.not_undef()?;
94 let catch_fn = this.read_scalar(catch_fn)?.not_undef()?;
96 // Now we make a function call, and pass `data` as first and only argument.
97 let f_instance = this.memory.get_fn(try_fn)?.as_instance()?;
98 trace!("try_fn: {:?}", f_instance);
99 let ret_place = MPlaceTy::dangling(this.machine.layouts.unit, this).into();
104 // Directly return to caller.
105 StackPopCleanup::Goto { ret: Some(ret), unwind: None },
108 // We ourselves will return `0`, eventually (will be overwritten if we catch a panic).
109 this.write_null(dest)?;
111 // In unwind mode, we tag this frame with the extra data needed to catch unwinding.
112 // This lets `handle_stack_pop` (below) know that we should stop unwinding
113 // when we pop this frame.
114 if this.tcx.sess.panic_strategy() == PanicStrategy::Unwind {
115 this.frame_mut().extra.catch_unwind = Some(CatchUnwindData { catch_fn, data, dest, ret });
123 mut extra: FrameData<'tcx>,
125 ) -> InterpResult<'tcx, StackPopJump> {
126 let this = self.eval_context_mut();
128 trace!("handle_stack_pop(extra = {:?}, unwinding = {})", extra, unwinding);
129 if let Some(stacked_borrows) = &this.memory.extra.stacked_borrows {
130 stacked_borrows.borrow_mut().end_call(extra.call_id);
133 // We only care about `catch_panic` if we're unwinding - if we're doing a normal
134 // return, then we don't need to do anything special.
135 if let (true, Some(catch_unwind)) = (unwinding, extra.catch_unwind.take()) {
136 // We've just popped a frame that was pushed by `try`,
137 // and we are unwinding, so we should catch that.
138 trace!("unwinding: found catch_panic frame during unwinding: {:?}", 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 // `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.machine.panic_payload.take().unwrap();
147 // Push the `catch_fn` stackframe.
148 let f_instance = this.memory.get_fn(catch_unwind.catch_fn)?.as_instance()?;
149 trace!("catch_fn: {:?}", f_instance);
150 let ret_place = MPlaceTy::dangling(this.machine.layouts.unit, this).into();
153 &[catch_unwind.data.into(), payload.into()],
155 // Directly return to caller of `try`.
156 StackPopCleanup::Goto { ret: Some(catch_unwind.ret), unwind: None },
159 // We pushed a new stack frame, the engine should not do any jumping now!
160 Ok(StackPopJump::NoJump)
162 Ok(StackPopJump::Normal)
166 /// Starta a panic in the interpreter with the given message as payload.
170 unwind: Option<mir::BasicBlock>,
171 ) -> InterpResult<'tcx> {
172 let this = self.eval_context_mut();
174 // First arg: message.
175 let msg = this.allocate_str(msg, MiriMemoryKind::Machine.into());
177 // Call the lang item.
178 let panic = this.tcx.lang_items().panic_fn().unwrap();
179 let panic = ty::Instance::mono(this.tcx.tcx, panic);
184 StackPopCleanup::Goto { ret: None, unwind },
190 msg: &mir::AssertMessage<'tcx>,
191 unwind: Option<mir::BasicBlock>,
192 ) -> InterpResult<'tcx> {
193 use rustc_middle::mir::AssertKind::*;
194 let this = self.eval_context_mut();
197 BoundsCheck { index, len } => {
198 // Forward to `panic_bounds_check` lang item.
201 let index = this.read_scalar(this.eval_operand(index, None)?)?;
203 let len = this.read_scalar(this.eval_operand(len, None)?)?;
205 // Call the lang item.
206 let panic_bounds_check = this.tcx.lang_items().panic_bounds_check_fn().unwrap();
207 let panic_bounds_check = ty::Instance::mono(this.tcx.tcx, panic_bounds_check);
210 &[index.into(), len.into()],
212 StackPopCleanup::Goto { ret: None, unwind },
216 // Forward everything else to `panic` lang item.
217 this.start_panic(msg.description(), unwind)?;