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 /// Check if panicking is supported on this target, and give a good error otherwise.
36 fn check_panic_supported(&self) -> InterpResult<'tcx> {
37 match self.eval_context_ref().tcx.sess.target.target.target_os.as_str() {
38 "linux" | "macos" => Ok(()),
39 _ => throw_unsup_format!("panicking is not supported on this target"),
43 /// Handles the special `miri_start_panic` intrinsic, which is called
44 /// by libpanic_unwind to delegate the actual unwinding process to Miri.
45 fn handle_miri_start_panic(
47 args: &[OpTy<'tcx, Tag>],
48 unwind: Option<mir::BasicBlock>,
49 ) -> InterpResult<'tcx> {
50 let this = self.eval_context_mut();
52 trace!("miri_start_panic: {:?}", this.frame().span);
54 // Get the raw pointer stored in arg[0] (the panic payload).
55 let payload = this.read_scalar(args[0])?.not_undef()?;
57 this.machine.panic_payload.is_none(),
58 "the panic runtime should avoid double-panics"
60 this.machine.panic_payload = Some(payload);
62 // Jump to the unwind block to begin unwinding.
63 this.unwind_to_block(unwind);
67 /// Handles the `try` intrinsic, the underlying implementation of `std::panicking::try`.
70 args: &[OpTy<'tcx, Tag>],
71 dest: PlaceTy<'tcx, Tag>,
73 ) -> InterpResult<'tcx> {
74 let this = self.eval_context_mut();
77 // fn r#try(try_fn: fn(*mut u8), data: *mut u8, catch_fn: fn(*mut u8, *mut u8)) -> i32
78 // Calls `try_fn` with `data` as argument. If that executes normally, returns 0.
79 // If that unwinds, calls `catch_fn` with the first argument being `data` and
80 // then second argument being a target-dependent `payload` (i.e. it is up to us to define
81 // what that is), and returns 1.
82 // The `payload` is passed (by libstd) to `__rust_panic_cleanup`, which is then expected to
83 // return a `Box<dyn Any + Send + 'static>`.
84 // In Miri, `miri_start_panic` is passed exactly that type, so we make the `payload` simply
85 // a pointer to `Box<dyn Any + Send + 'static>`.
87 // Get all the arguments.
88 let try_fn = this.read_scalar(args[0])?.not_undef()?;
89 let data = this.read_scalar(args[1])?.not_undef()?;
90 let catch_fn = this.read_scalar(args[2])?.not_undef()?;
92 // Now we make a function call, and pass `data` as first and only argument.
93 let f_instance = this.memory.get_fn(try_fn)?.as_instance()?;
94 trace!("try_fn: {:?}", f_instance);
95 let ret_place = MPlaceTy::dangling(this.layout_of(this.tcx.mk_unit())?, this).into();
100 // Directly return to caller.
101 StackPopCleanup::Goto { ret: Some(ret), unwind: None },
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 = Some(CatchUnwindData { catch_fn, data, dest, ret });
119 mut extra: FrameData<'tcx>,
121 ) -> InterpResult<'tcx, StackPopJump> {
122 let this = self.eval_context_mut();
124 trace!("handle_stack_pop(extra = {:?}, unwinding = {})", extra, unwinding);
125 if let Some(stacked_borrows) = this.memory.extra.stacked_borrows.as_ref() {
126 stacked_borrows.borrow_mut().end_call(extra.call_id);
129 // We only care about `catch_panic` if we're unwinding - if we're doing a normal
130 // return, then we don't need to do anything special.
131 if let (true, Some(catch_unwind)) = (unwinding, extra.catch_unwind.take()) {
132 // We've just popped a frame that was pushed by `try`,
133 // and we are unwinding, so we should catch that.
134 trace!("unwinding: found catch_panic frame during unwinding: {:?}", this.frame().span);
136 // We set the return value of `try` to 1, since there was a panic.
137 this.write_scalar(Scalar::from_i32(1), catch_unwind.dest)?;
139 // `panic_payload` holds what was passed to `miri_start_panic`.
140 // This is exactly the second argument we need to pass to `catch_fn`.
141 let payload = this.machine.panic_payload.take().unwrap();
143 // Push the `catch_fn` stackframe.
144 let f_instance = this.memory.get_fn(catch_unwind.catch_fn)?.as_instance()?;
145 trace!("catch_fn: {:?}", f_instance);
146 let ret_place = MPlaceTy::dangling(this.layout_of(this.tcx.mk_unit())?, this).into();
149 &[catch_unwind.data.into(), payload.into()],
151 // Directly return to caller of `try`.
152 StackPopCleanup::Goto { ret: Some(catch_unwind.ret), unwind: None },
155 // We pushed a new stack frame, the engine should not do any jumping now!
156 Ok(StackPopJump::NoJump)
158 Ok(StackPopJump::Normal)
162 /// Starta a panic in the interpreter with the given message as payload.
166 unwind: Option<mir::BasicBlock>,
167 ) -> InterpResult<'tcx> {
168 let this = self.eval_context_mut();
170 // First arg: message.
171 let msg = this.allocate_str(msg, MiriMemoryKind::Machine.into());
173 // Call the lang item.
174 let panic = this.tcx.lang_items().panic_fn().unwrap();
175 let panic = ty::Instance::mono(this.tcx.tcx, panic);
180 StackPopCleanup::Goto { ret: None, unwind },
186 msg: &mir::AssertMessage<'tcx>,
187 unwind: Option<mir::BasicBlock>,
188 ) -> InterpResult<'tcx> {
189 use rustc::mir::AssertKind::*;
190 let this = self.eval_context_mut();
193 BoundsCheck { ref index, ref len } => {
194 // Forward to `panic_bounds_check` lang item.
197 let index = this.read_scalar(this.eval_operand(index, None)?)?;
199 let len = this.read_scalar(this.eval_operand(len, None)?)?;
201 // Call the lang item.
202 let panic_bounds_check = this.tcx.lang_items().panic_bounds_check_fn().unwrap();
203 let panic_bounds_check = ty::Instance::mono(this.tcx.tcx, panic_bounds_check);
206 &[index.into(), len.into()],
208 StackPopCleanup::Goto { ret: None, unwind },
212 // Forward everything else to `panic` lang item.
213 this.start_panic(msg.description(), unwind)?;