miri/shims/panic.rs
1//! Panic runtime for Miri.
2//!
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_unwind` intrinsic instead of the
7//! target-native panic runtime. (This lives in the rustc repo.)
8//! - An implementation of `miri_start_unwind` 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.
13
14use rustc_abi::ExternAbi;
15use rustc_middle::{mir, ty};
16use rustc_target::spec::PanicStrategy;
17
18use self::helpers::check_intrinsic_arg_count;
19use crate::*;
20
21/// Holds all of the relevant data for when unwinding hits a `try` frame.
22#[derive(Debug)]
23pub struct CatchUnwindData<'tcx> {
24 /// The `catch_fn` callback to call in case of a panic.
25 catch_fn: Pointer,
26 /// The `data` argument for that callback.
27 data: ImmTy<'tcx>,
28 /// The return place from the original call to `try`.
29 dest: MPlaceTy<'tcx>,
30 /// The return block from the original call to `try`.
31 ret: Option<mir::BasicBlock>,
32}
33
34impl VisitProvenance for CatchUnwindData<'_> {
35 fn visit_provenance(&self, visit: &mut VisitWith<'_>) {
36 let CatchUnwindData { catch_fn, data, dest, ret: _ } = self;
37 catch_fn.visit_provenance(visit);
38 data.visit_provenance(visit);
39 dest.visit_provenance(visit);
40 }
41}
42
43impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
44pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
45 /// Handles the special `miri_start_unwind` intrinsic, which is called
46 /// by libpanic_unwind to delegate the actual unwinding process to Miri.
47 fn handle_miri_start_unwind(&mut self, payload: &OpTy<'tcx>) -> InterpResult<'tcx> {
48 let this = self.eval_context_mut();
49
50 trace!("miri_start_unwind: {:?}", this.frame().instance());
51
52 let payload = this.read_immediate(payload)?;
53 let thread = this.active_thread_mut();
54 thread.panic_payloads.push(payload);
55
56 interp_ok(())
57 }
58
59 /// Handles the `catch_unwind` intrinsic.
60 fn handle_catch_unwind(
61 &mut self,
62 args: &[OpTy<'tcx>],
63 dest: &MPlaceTy<'tcx>,
64 ret: Option<mir::BasicBlock>,
65 ) -> InterpResult<'tcx> {
66 let this = self.eval_context_mut();
67
68 // Signature:
69 // fn catch_unwind(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_unwind` is passed exactly that type, so we make the `payload` simply
77 // a pointer to `Box<dyn Any + Send + 'static>`.
78
79 // Get all the arguments.
80 let [try_fn, data, catch_fn] = check_intrinsic_arg_count(args)?;
81 let try_fn = this.read_pointer(try_fn)?;
82 let data = this.read_immediate(data)?;
83 let catch_fn = this.read_pointer(catch_fn)?;
84
85 // Now we make a function call, and pass `data` as first and only argument.
86 let f_instance = this.get_ptr_fn(try_fn)?.as_instance()?;
87 trace!("try_fn: {:?}", f_instance);
88 #[allow(clippy::cloned_ref_to_slice_refs)] // the code is clearer as-is
89 this.call_function(
90 f_instance,
91 ExternAbi::Rust,
92 &[data.clone()],
93 None,
94 // Directly return to caller.
95 StackPopCleanup::Goto { ret, unwind: mir::UnwindAction::Continue },
96 )?;
97
98 // We ourselves will return `0`, eventually (will be overwritten if we catch a panic).
99 this.write_null(dest)?;
100
101 // In unwind mode, we tag this frame with the extra data needed to catch unwinding.
102 // This lets `handle_stack_pop` (below) know that we should stop unwinding
103 // when we pop this frame.
104 if this.tcx.sess.panic_strategy() == PanicStrategy::Unwind {
105 this.frame_mut().extra.catch_unwind =
106 Some(CatchUnwindData { catch_fn, data, dest: dest.clone(), ret });
107 }
108
109 interp_ok(())
110 }
111
112 fn handle_stack_pop_unwind(
113 &mut self,
114 mut extra: FrameExtra<'tcx>,
115 unwinding: bool,
116 ) -> InterpResult<'tcx, ReturnAction> {
117 let this = self.eval_context_mut();
118 trace!("handle_stack_pop_unwind(extra = {:?}, unwinding = {})", extra, unwinding);
119
120 // We only care about `catch_panic` if we're unwinding - if we're doing a normal
121 // return, then we don't need to do anything special.
122 if let (true, Some(catch_unwind)) = (unwinding, extra.catch_unwind.take()) {
123 // We've just popped a frame that was pushed by `catch_unwind`,
124 // and we are unwinding, so we should catch that.
125 trace!(
126 "unwinding: found catch_panic frame during unwinding: {:?}",
127 this.frame().instance()
128 );
129
130 // We set the return value of `catch_unwind` to 1, since there was a panic.
131 this.write_scalar(Scalar::from_i32(1), &catch_unwind.dest)?;
132
133 // The Thread's `panic_payload` holds what was passed to `miri_start_unwind`.
134 // This is exactly the second argument we need to pass to `catch_fn`.
135 let payload = this.active_thread_mut().panic_payloads.pop().unwrap();
136
137 // Push the `catch_fn` stackframe.
138 let f_instance = this.get_ptr_fn(catch_unwind.catch_fn)?.as_instance()?;
139 trace!("catch_fn: {:?}", f_instance);
140 this.call_function(
141 f_instance,
142 ExternAbi::Rust,
143 &[catch_unwind.data, payload],
144 None,
145 // Directly return to caller of `catch_unwind`.
146 StackPopCleanup::Goto {
147 ret: catch_unwind.ret,
148 // `catch_fn` must not unwind.
149 unwind: mir::UnwindAction::Unreachable,
150 },
151 )?;
152
153 // We pushed a new stack frame, the engine should not do any jumping now!
154 interp_ok(ReturnAction::NoJump)
155 } else {
156 interp_ok(ReturnAction::Normal)
157 }
158 }
159
160 /// Start a panic in the interpreter with the given message as payload.
161 fn start_panic(&mut self, msg: &str, unwind: mir::UnwindAction) -> InterpResult<'tcx> {
162 let this = self.eval_context_mut();
163
164 // First arg: message.
165 let msg = this.allocate_str_dedup(msg)?;
166
167 // Call the lang item.
168 let panic = this.tcx.lang_items().panic_fn().unwrap();
169 let panic = ty::Instance::mono(this.tcx.tcx, panic);
170 this.call_function(
171 panic,
172 ExternAbi::Rust,
173 &[this.mplace_to_ref(&msg)?],
174 None,
175 StackPopCleanup::Goto { ret: None, unwind },
176 )
177 }
178
179 /// Start a non-unwinding panic in the interpreter with the given message as payload.
180 fn start_panic_nounwind(&mut self, msg: &str) -> InterpResult<'tcx> {
181 let this = self.eval_context_mut();
182
183 // First arg: message.
184 let msg = this.allocate_str_dedup(msg)?;
185
186 // Call the lang item.
187 let panic = this.tcx.lang_items().panic_nounwind().unwrap();
188 let panic = ty::Instance::mono(this.tcx.tcx, panic);
189 this.call_function(
190 panic,
191 ExternAbi::Rust,
192 &[this.mplace_to_ref(&msg)?],
193 None,
194 StackPopCleanup::Goto { ret: None, unwind: mir::UnwindAction::Unreachable },
195 )
196 }
197
198 fn assert_panic(
199 &mut self,
200 msg: &mir::AssertMessage<'tcx>,
201 unwind: mir::UnwindAction,
202 ) -> InterpResult<'tcx> {
203 use rustc_middle::mir::AssertKind::*;
204 let this = self.eval_context_mut();
205
206 match msg {
207 BoundsCheck { index, len } => {
208 // Forward to `panic_bounds_check` lang item.
209
210 // First arg: index.
211 let index = this.read_immediate(&this.eval_operand(index, None)?)?;
212 // Second arg: len.
213 let len = this.read_immediate(&this.eval_operand(len, None)?)?;
214
215 // Call the lang item.
216 let panic_bounds_check = this.tcx.lang_items().panic_bounds_check_fn().unwrap();
217 let panic_bounds_check = ty::Instance::mono(this.tcx.tcx, panic_bounds_check);
218 this.call_function(
219 panic_bounds_check,
220 ExternAbi::Rust,
221 &[index, len],
222 None,
223 StackPopCleanup::Goto { ret: None, unwind },
224 )?;
225 }
226 MisalignedPointerDereference { required, found } => {
227 // Forward to `panic_misaligned_pointer_dereference` lang item.
228
229 // First arg: required.
230 let required = this.read_immediate(&this.eval_operand(required, None)?)?;
231 // Second arg: found.
232 let found = this.read_immediate(&this.eval_operand(found, None)?)?;
233
234 // Call the lang item.
235 let panic_misaligned_pointer_dereference =
236 this.tcx.lang_items().panic_misaligned_pointer_dereference_fn().unwrap();
237 let panic_misaligned_pointer_dereference =
238 ty::Instance::mono(this.tcx.tcx, panic_misaligned_pointer_dereference);
239 this.call_function(
240 panic_misaligned_pointer_dereference,
241 ExternAbi::Rust,
242 &[required, found],
243 None,
244 StackPopCleanup::Goto { ret: None, unwind },
245 )?;
246 }
247
248 _ => {
249 // Call the lang item associated with this message.
250 let fn_item = this.tcx.require_lang_item(msg.panic_function(), None);
251 let instance = ty::Instance::mono(this.tcx.tcx, fn_item);
252 this.call_function(
253 instance,
254 ExternAbi::Rust,
255 &[],
256 None,
257 StackPopCleanup::Goto { ret: None, unwind },
258 )?;
259 }
260 }
261 interp_ok(())
262 }
263}