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;
18 use rustc_target::spec::abi::Abi;
21 use helpers::check_arg_count;
23 /// Holds all of the relevant data for when unwinding hits a `try` frame.
25 pub struct CatchUnwindData<'tcx> {
26 /// The `catch_fn` callback to call in case of a panic.
27 catch_fn: Scalar<Tag>,
28 /// The `data` argument for that callback.
30 /// The return place from the original call to `try`.
31 dest: PlaceTy<'tcx, Tag>,
32 /// The return block from the original call to `try`.
36 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
37 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.
40 fn handle_miri_start_panic(
42 args: &[OpTy<'tcx, Tag>],
43 unwind: Option<mir::BasicBlock>,
44 ) -> InterpResult<'tcx> {
45 let this = self.eval_context_mut();
47 trace!("miri_start_panic: {:?}", this.frame().instance);
48 // Make sure we only start unwinding when this matches our panic strategy.
49 if this.tcx.sess.panic_strategy() != PanicStrategy::Unwind {
50 throw_ub_format!("unwinding despite panic=abort");
53 // Get the raw pointer stored in arg[0] (the panic payload).
54 let &[ref payload] = check_arg_count(args)?;
55 let payload = this.read_scalar(payload)?.check_init()?;
56 let thread = this.active_thread_mut();
58 thread.panic_payload.is_none(),
59 "the panic runtime should avoid double-panics"
61 thread.panic_payload = Some(payload);
63 // Jump to the unwind block to begin unwinding.
64 this.unwind_to_block(unwind);
68 /// Handles the `try` intrinsic, the underlying implementation of `std::panicking::try`.
71 args: &[OpTy<'tcx, Tag>],
72 dest: &PlaceTy<'tcx, Tag>,
74 ) -> InterpResult<'tcx> {
75 let this = self.eval_context_mut();
78 // fn r#try(try_fn: fn(*mut u8), data: *mut u8, catch_fn: fn(*mut u8, *mut u8)) -> i32
79 // Calls `try_fn` with `data` as argument. If that executes normally, returns 0.
80 // If that unwinds, calls `catch_fn` with the first argument being `data` and
81 // then second argument being a target-dependent `payload` (i.e. it is up to us to define
82 // what that is), and returns 1.
83 // The `payload` is passed (by libstd) to `__rust_panic_cleanup`, which is then expected to
84 // return a `Box<dyn Any + Send + 'static>`.
85 // In Miri, `miri_start_panic` is passed exactly that type, so we make the `payload` simply
86 // a pointer to `Box<dyn Any + Send + 'static>`.
88 // Get all the arguments.
89 let &[ref try_fn, ref data, ref catch_fn] = check_arg_count(args)?;
90 let try_fn = this.read_scalar(try_fn)?.check_init()?;
91 let data = this.read_scalar(data)?.check_init()?;
92 let catch_fn = this.read_scalar(catch_fn)?.check_init()?;
94 // Now we make a function call, and pass `data` as first and only argument.
95 let f_instance = this.memory.get_fn(try_fn)?.as_instance()?;
96 trace!("try_fn: {:?}", f_instance);
97 let ret_place = MPlaceTy::dangling(this.machine.layouts.unit, this).into();
103 // Directly return to caller.
104 StackPopCleanup::Goto { ret: Some(ret), unwind: None },
107 // We ourselves will return `0`, eventually (will be overwritten if we catch a panic).
108 this.write_null(dest)?;
110 // In unwind mode, we tag this frame with the extra data needed to catch unwinding.
111 // This lets `handle_stack_pop` (below) know that we should stop unwinding
112 // when we pop this frame.
113 if this.tcx.sess.panic_strategy() == PanicStrategy::Unwind {
114 this.frame_mut().extra.catch_unwind = Some(CatchUnwindData { catch_fn, data, dest: *dest, ret });
122 mut extra: FrameData<'tcx>,
124 ) -> InterpResult<'tcx, StackPopJump> {
125 let this = self.eval_context_mut();
127 trace!("handle_stack_pop(extra = {:?}, unwinding = {})", extra, unwinding);
128 if let Some(stacked_borrows) = &this.memory.extra.stacked_borrows {
129 stacked_borrows.borrow_mut().end_call(extra.call_id);
132 // We only care about `catch_panic` if we're unwinding - if we're doing a normal
133 // return, then we don't need to do anything special.
134 if let (true, Some(catch_unwind)) = (unwinding, extra.catch_unwind.take()) {
135 // We've just popped a frame that was pushed by `try`,
136 // and we are unwinding, so we should catch that.
137 trace!("unwinding: found catch_panic frame during unwinding: {:?}", this.frame().instance);
139 // We set the return value of `try` to 1, since there was a panic.
140 this.write_scalar(Scalar::from_i32(1), &catch_unwind.dest)?;
142 // The Thread's `panic_payload` holds what was passed to `miri_start_panic`.
143 // This is exactly the second argument we need to pass to `catch_fn`.
144 let payload = this.active_thread_mut().panic_payload.take().unwrap();
146 // Push the `catch_fn` stackframe.
147 let f_instance = this.memory.get_fn(catch_unwind.catch_fn)?.as_instance()?;
148 trace!("catch_fn: {:?}", f_instance);
149 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);
185 StackPopCleanup::Goto { ret: None, unwind },
191 msg: &mir::AssertMessage<'tcx>,
192 unwind: Option<mir::BasicBlock>,
193 ) -> InterpResult<'tcx> {
194 use rustc_middle::mir::AssertKind::*;
195 let this = self.eval_context_mut();
198 BoundsCheck { index, len } => {
199 // Forward to `panic_bounds_check` lang item.
202 let index = this.read_scalar(&this.eval_operand(index, None)?)?;
204 let len = this.read_scalar(&this.eval_operand(len, None)?)?;
206 // Call the lang item.
207 let panic_bounds_check = this.tcx.lang_items().panic_bounds_check_fn().unwrap();
208 let panic_bounds_check = ty::Instance::mono(this.tcx.tcx, panic_bounds_check);
212 &[index.into(), len.into()],
214 StackPopCleanup::Goto { ret: None, unwind },
218 // Forward everything else to `panic` lang item.
219 this.start_panic(msg.description(), unwind)?;