wasmtime/runtime/trap.rs
1#[cfg(feature = "coredump")]
2use super::coredump::WasmCoreDump;
3#[cfg(feature = "gc")]
4use crate::ThrownException;
5use crate::prelude::*;
6use crate::store::StoreOpaque;
7use crate::{AsContext, Module};
8use core::fmt;
9use wasmtime_environ::{FilePos, demangle_function_name, demangle_function_name_or_index};
10
11/// Representation of a WebAssembly trap and what caused it to occur.
12///
13/// WebAssembly traps happen explicitly for instructions such as `unreachable`
14/// but can also happen as side effects of other instructions such as `i32.load`
15/// loading an out-of-bounds address. Traps halt the execution of WebAssembly
16/// and cause an error to be returned to the host. This enumeration is a list of
17/// all possible traps that can happen in wasm, in addition to some
18/// Wasmtime-specific trap codes listed here as well.
19///
20/// # Errors in Wasmtime
21///
22/// Error-handling in Wasmtime is primarily done through the
23/// [`anyhow`][mod@anyhow] crate where most results are a
24/// [`Result<T>`](anyhow::Result) which is an alias for [`Result<T,
25/// anyhow::Error>`](std::result::Result). Errors in Wasmtime are represented
26/// with [`anyhow::Error`] which acts as a container for any type of error in
27/// addition to optional context for this error. The "base" error or
28/// [`anyhow::Error::root_cause`] is a [`Trap`] whenever WebAssembly hits a
29/// trap, or otherwise it's whatever the host created the error with when
30/// returning an error for a host call.
31///
32/// Any error which happens while WebAssembly is executing will also, by
33/// default, capture a backtrace of the wasm frames while executing. This
34/// backtrace is represented with a [`WasmBacktrace`] instance and is attached
35/// to the [`anyhow::Error`] return value as a
36/// [`context`](anyhow::Error::context). Inspecting a [`WasmBacktrace`] can be
37/// done with the [`downcast_ref`](anyhow::Error::downcast_ref) function. For
38/// information on this see the [`WasmBacktrace`] documentation.
39///
40/// # Examples
41///
42/// ```
43/// # use wasmtime::*;
44/// # fn main() -> Result<()> {
45/// let engine = Engine::default();
46/// let module = Module::new(
47/// &engine,
48/// r#"
49/// (module
50/// (func (export "trap")
51/// unreachable)
52/// (func $overflow (export "overflow")
53/// call $overflow)
54/// )
55/// "#,
56/// )?;
57/// let mut store = Store::new(&engine, ());
58/// let instance = Instance::new(&mut store, &module, &[])?;
59///
60/// let trap = instance.get_typed_func::<(), ()>(&mut store, "trap")?;
61/// let error = trap.call(&mut store, ()).unwrap_err();
62/// assert_eq!(*error.downcast_ref::<Trap>().unwrap(), Trap::UnreachableCodeReached);
63/// assert!(error.root_cause().is::<Trap>());
64///
65/// let overflow = instance.get_typed_func::<(), ()>(&mut store, "overflow")?;
66/// let error = overflow.call(&mut store, ()).unwrap_err();
67/// assert_eq!(*error.downcast_ref::<Trap>().unwrap(), Trap::StackOverflow);
68/// # Ok(())
69/// # }
70/// ```
71pub use wasmtime_environ::Trap;
72
73#[cold] // traps are exceptional, this helps move handling off the main path
74pub(crate) fn from_runtime_box(
75 store: &mut StoreOpaque,
76 runtime_trap: Box<crate::runtime::vm::Trap>,
77) -> Error {
78 let crate::runtime::vm::Trap {
79 reason,
80 backtrace,
81 coredumpstack,
82 } = *runtime_trap;
83 let (mut error, pc) = match reason {
84 #[cfg(feature = "gc")]
85 crate::runtime::vm::TrapReason::Exception => (ThrownException.into(), None),
86 // For user-defined errors they're already an `anyhow::Error` so no
87 // conversion is really necessary here, but a `backtrace` may have
88 // been captured so it's attempted to get inserted here.
89 //
90 // If the error is actually a `Trap` then the backtrace is inserted
91 // directly into the `Trap` since there's storage there for it.
92 // Otherwise though this represents a host-defined error which isn't
93 // using a `Trap` but instead some other condition that was fatal to
94 // wasm itself. In that situation the backtrace is inserted as
95 // contextual information on error using `error.context(...)` to
96 // provide useful information to debug with for the embedder/caller,
97 // otherwise the information about what the wasm was doing when the
98 // error was generated would be lost.
99 crate::runtime::vm::TrapReason::User(error) => (error, None),
100 crate::runtime::vm::TrapReason::Jit {
101 pc,
102 faulting_addr,
103 trap,
104 } => {
105 let mut err: Error = trap.into();
106
107 // If a fault address was present, for example with segfaults,
108 // then simultaneously assert that it's within a known linear memory
109 // and additionally translate it to a wasm-local address to be added
110 // as context to the error.
111 if let Some(fault) = faulting_addr.and_then(|addr| store.wasm_fault(pc, addr)) {
112 err = err.context(fault);
113 }
114 (err, Some(pc))
115 }
116 crate::runtime::vm::TrapReason::Wasm(trap_code) => (trap_code.into(), None),
117 };
118
119 if let Some(bt) = backtrace {
120 let bt = WasmBacktrace::from_captured(store, bt, pc);
121 if !bt.wasm_trace.is_empty() {
122 error = error.context(bt);
123 }
124 }
125
126 let _ = &coredumpstack;
127 #[cfg(feature = "coredump")]
128 if let Some(coredump) = coredumpstack {
129 let bt = WasmBacktrace::from_captured(store, coredump.bt, pc);
130 let cd = WasmCoreDump::new(store, bt);
131 error = error.context(cd);
132 }
133
134 error
135}
136
137/// Representation of a backtrace of function frames in a WebAssembly module for
138/// where an error happened.
139///
140/// This structure is attached to the [`anyhow::Error`] returned from many
141/// Wasmtime functions that execute WebAssembly such as [`Instance::new`] or
142/// [`Func::call`]. This can be acquired with the [`anyhow::Error::downcast`]
143/// family of methods to programmatically inspect the backtrace. Otherwise since
144/// it's part of the error returned this will get printed along with the rest of
145/// the error when the error is logged.
146///
147/// Capturing of wasm backtraces can be configured through the
148/// [`Config::wasm_backtrace`](crate::Config::wasm_backtrace) method.
149///
150/// For more information about errors in wasmtime see the documentation of the
151/// [`Trap`] type.
152///
153/// [`Func::call`]: crate::Func::call
154/// [`Instance::new`]: crate::Instance::new
155///
156/// # Examples
157///
158/// ```
159/// # use wasmtime::*;
160/// # fn main() -> Result<()> {
161/// let engine = Engine::default();
162/// let module = Module::new(
163/// &engine,
164/// r#"
165/// (module
166/// (func $start (export "run")
167/// call $trap)
168/// (func $trap
169/// unreachable)
170/// )
171/// "#,
172/// )?;
173/// let mut store = Store::new(&engine, ());
174/// let instance = Instance::new(&mut store, &module, &[])?;
175/// let func = instance.get_typed_func::<(), ()>(&mut store, "run")?;
176/// let error = func.call(&mut store, ()).unwrap_err();
177/// let bt = error.downcast_ref::<WasmBacktrace>().unwrap();
178/// let frames = bt.frames();
179/// assert_eq!(frames.len(), 2);
180/// assert_eq!(frames[0].func_name(), Some("trap"));
181/// assert_eq!(frames[1].func_name(), Some("start"));
182/// # Ok(())
183/// # }
184/// ```
185#[derive(Debug)]
186pub struct WasmBacktrace {
187 wasm_trace: Vec<FrameInfo>,
188 hint_wasm_backtrace_details_env: bool,
189 // This is currently only present for the `Debug` implementation for extra
190 // context.
191 _runtime_trace: crate::runtime::vm::Backtrace,
192}
193
194impl WasmBacktrace {
195 /// Captures a trace of the WebAssembly frames on the stack for the
196 /// provided store.
197 ///
198 /// This will return a [`WasmBacktrace`] which holds captured
199 /// [`FrameInfo`]s for each frame of WebAssembly on the call stack of the
200 /// current thread. If no WebAssembly is on the stack then the returned
201 /// backtrace will have no frames in it.
202 ///
203 /// Note that this function will respect the [`Config::wasm_backtrace`]
204 /// configuration option and will return an empty backtrace if that is
205 /// disabled. To always capture a backtrace use the
206 /// [`WasmBacktrace::force_capture`] method.
207 ///
208 /// Also note that this function will only capture frames from the
209 /// specified `store` on the stack, ignoring frames from other stores if
210 /// present.
211 ///
212 /// [`Config::wasm_backtrace`]: crate::Config::wasm_backtrace
213 ///
214 /// # Example
215 ///
216 /// ```
217 /// # use wasmtime::*;
218 /// # fn main() -> Result<()> {
219 /// let engine = Engine::default();
220 /// let module = Module::new(
221 /// &engine,
222 /// r#"
223 /// (module
224 /// (import "" "" (func $host))
225 /// (func $foo (export "f") call $bar)
226 /// (func $bar call $host)
227 /// )
228 /// "#,
229 /// )?;
230 ///
231 /// let mut store = Store::new(&engine, ());
232 /// let func = Func::wrap(&mut store, |cx: Caller<'_, ()>| {
233 /// let trace = WasmBacktrace::capture(&cx);
234 /// println!("{trace:?}");
235 /// });
236 /// let instance = Instance::new(&mut store, &module, &[func.into()])?;
237 /// let func = instance.get_typed_func::<(), ()>(&mut store, "f")?;
238 /// func.call(&mut store, ())?;
239 /// # Ok(())
240 /// # }
241 /// ```
242 pub fn capture(store: impl AsContext) -> WasmBacktrace {
243 let store = store.as_context();
244 if store.engine().config().wasm_backtrace {
245 Self::force_capture(store)
246 } else {
247 WasmBacktrace {
248 wasm_trace: Vec::new(),
249 hint_wasm_backtrace_details_env: false,
250 _runtime_trace: crate::runtime::vm::Backtrace::empty(),
251 }
252 }
253 }
254
255 /// Unconditionally captures a trace of the WebAssembly frames on the stack
256 /// for the provided store.
257 ///
258 /// Same as [`WasmBacktrace::capture`] except that it disregards the
259 /// [`Config::wasm_backtrace`](crate::Config::wasm_backtrace) setting and
260 /// always captures a backtrace.
261 pub fn force_capture(store: impl AsContext) -> WasmBacktrace {
262 let store = store.as_context();
263 Self::from_captured(store.0, crate::runtime::vm::Backtrace::new(store.0), None)
264 }
265
266 fn from_captured(
267 store: &StoreOpaque,
268 runtime_trace: crate::runtime::vm::Backtrace,
269 trap_pc: Option<usize>,
270 ) -> Self {
271 let mut wasm_trace = Vec::<FrameInfo>::with_capacity(runtime_trace.frames().len());
272 let mut hint_wasm_backtrace_details_env = false;
273 let wasm_backtrace_details_env_used =
274 store.engine().config().wasm_backtrace_details_env_used;
275
276 for frame in runtime_trace.frames() {
277 debug_assert!(frame.pc() != 0);
278
279 // Note that we need to be careful about the pc we pass in
280 // here to lookup frame information. This program counter is
281 // used to translate back to an original source location in
282 // the origin wasm module. If this pc is the exact pc that
283 // the trap happened at, then we look up that pc precisely.
284 // Otherwise backtrace information typically points at the
285 // pc *after* the call instruction (because otherwise it's
286 // likely a call instruction on the stack). In that case we
287 // want to lookup information for the previous instruction
288 // (the call instruction) so we subtract one as the lookup.
289 let pc_to_lookup = if Some(frame.pc()) == trap_pc {
290 frame.pc()
291 } else {
292 frame.pc() - 1
293 };
294
295 // NB: The PC we are looking up _must_ be a Wasm PC since
296 // `crate::runtime::vm::Backtrace` only contains Wasm frames.
297 //
298 // However, consider the case where we have multiple, nested calls
299 // across stores (with host code in between, by necessity, since
300 // only things in the same store can be linked directly together):
301 //
302 // | ... |
303 // | Host | |
304 // +-----------------+ | stack
305 // | Wasm in store A | | grows
306 // +-----------------+ | down
307 // | Host | |
308 // +-----------------+ |
309 // | Wasm in store B | V
310 // +-----------------+
311 //
312 // In this scenario, the `crate::runtime::vm::Backtrace` will
313 // contain two frames: Wasm in store B followed by Wasm in store
314 // A. But `store.modules()` will only have the module information
315 // for modules instantiated within this store. Therefore, we use `if
316 // let Some(..)` instead of the `unwrap` you might otherwise expect
317 // and we ignore frames from modules that were not registered in
318 // this store's module registry.
319 if let Some((info, module)) = store.modules().lookup_frame_info(pc_to_lookup) {
320 wasm_trace.push(info);
321
322 // If this frame has unparsed debug information and the
323 // store's configuration indicates that we were
324 // respecting the environment variable of whether to
325 // do this then we will print out a helpful note in
326 // `Display` to indicate that more detailed information
327 // in a trap may be available.
328 let has_unparsed_debuginfo =
329 module.module().compiled_module().has_unparsed_debuginfo();
330 if has_unparsed_debuginfo
331 && wasm_backtrace_details_env_used
332 && cfg!(feature = "addr2line")
333 {
334 hint_wasm_backtrace_details_env = true;
335 }
336 }
337 }
338
339 Self {
340 wasm_trace,
341 _runtime_trace: runtime_trace,
342 hint_wasm_backtrace_details_env,
343 }
344 }
345
346 /// Returns a list of function frames in WebAssembly this backtrace
347 /// represents.
348 pub fn frames(&self) -> &[FrameInfo] {
349 self.wasm_trace.as_slice()
350 }
351}
352
353impl fmt::Display for WasmBacktrace {
354 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
355 writeln!(f, "error while executing at wasm backtrace:")?;
356
357 let mut needs_newline = false;
358 for (i, frame) in self.wasm_trace.iter().enumerate() {
359 // Avoid putting a trailing newline on the output
360 if needs_newline {
361 writeln!(f, "")?;
362 } else {
363 needs_newline = true;
364 }
365 let name = frame.module().name().unwrap_or("<unknown>");
366 write!(f, " {i:>3}: ")?;
367
368 if let Some(offset) = frame.module_offset() {
369 write!(f, "{offset:#8x} - ")?;
370 }
371
372 let write_raw_func_name = |f: &mut fmt::Formatter<'_>| {
373 demangle_function_name_or_index(f, frame.func_name(), frame.func_index() as usize)
374 };
375 if frame.symbols().is_empty() {
376 write!(f, "{name}!")?;
377 write_raw_func_name(f)?;
378 } else {
379 for (i, symbol) in frame.symbols().iter().enumerate() {
380 if i > 0 {
381 if needs_newline {
382 writeln!(f, "")?;
383 } else {
384 needs_newline = true;
385 }
386 write!(f, " - ")?;
387 } else {
388 // ...
389 }
390 match symbol.name() {
391 Some(name) => demangle_function_name(f, name)?,
392 None if i == 0 => write_raw_func_name(f)?,
393 None => write!(f, "<inlined function>")?,
394 }
395 if let Some(file) = symbol.file() {
396 writeln!(f, "")?;
397 write!(f, " at {file}")?;
398 if let Some(line) = symbol.line() {
399 write!(f, ":{line}")?;
400 if let Some(col) = symbol.column() {
401 write!(f, ":{col}")?;
402 }
403 }
404 }
405 }
406 }
407 }
408 if self.hint_wasm_backtrace_details_env {
409 write!(
410 f,
411 "\nnote: using the `WASMTIME_BACKTRACE_DETAILS=1` \
412 environment variable may show more debugging information"
413 )?;
414 }
415 Ok(())
416 }
417}
418
419/// Description of a frame in a backtrace for a [`WasmBacktrace`].
420///
421/// Whenever an error happens while WebAssembly is executing a
422/// [`WasmBacktrace`] will be attached to the error returned which can be used
423/// to acquire this `FrameInfo`. For more information see [`WasmBacktrace`].
424#[derive(Debug)]
425pub struct FrameInfo {
426 module: Module,
427 func_index: u32,
428 func_name: Option<String>,
429 func_start: FilePos,
430 instr: Option<FilePos>,
431 symbols: Vec<FrameSymbol>,
432}
433
434impl FrameInfo {
435 /// Fetches frame information about a program counter in a backtrace.
436 ///
437 /// Returns an object if this `pc` is known to this module, or returns `None`
438 /// if no information can be found.
439 pub(crate) fn new(module: Module, text_offset: usize) -> Option<FrameInfo> {
440 let compiled_module = module.compiled_module();
441 let index = compiled_module.func_by_text_offset(text_offset)?;
442 let func_start = compiled_module.func_start_srcloc(index);
443 let instr =
444 wasmtime_environ::lookup_file_pos(module.engine_code().address_map_data(), text_offset);
445 let index = compiled_module.module().func_index(index);
446 let func_index = index.as_u32();
447 let func_name = compiled_module.func_name(index).map(|s| s.to_string());
448
449 // In debug mode for now assert that we found a mapping for `pc` within
450 // the function, because otherwise something is buggy along the way and
451 // not accounting for all the instructions. This isn't super critical
452 // though so we can omit this check in release mode.
453 //
454 // Note that if the module doesn't even have an address map due to
455 // compilation settings then it's expected that `instr` is `None`.
456 debug_assert!(
457 instr.is_some() || !compiled_module.has_address_map(),
458 "failed to find instruction for {text_offset:#x}"
459 );
460
461 // Use our wasm-relative pc to symbolize this frame. If there's a
462 // symbolication context (dwarf debug info) available then we can try to
463 // look this up there.
464 //
465 // Note that dwarf pcs are code-section-relative, hence the subtraction
466 // from the location of `instr`. Also note that all errors are ignored
467 // here for now since technically wasm modules can always have any
468 // custom section contents.
469 let mut symbols = Vec::new();
470
471 let _ = &mut symbols;
472 #[cfg(feature = "addr2line")]
473 if let Some(s) = &compiled_module.symbolize_context().ok().and_then(|c| c) {
474 if let Some(offset) = instr.and_then(|i| i.file_offset()) {
475 let to_lookup = u64::from(offset) - s.code_section_offset();
476 if let Ok(mut frames) = s.addr2line().find_frames(to_lookup).skip_all_loads() {
477 while let Ok(Some(frame)) = frames.next() {
478 symbols.push(FrameSymbol {
479 name: frame
480 .function
481 .as_ref()
482 .and_then(|l| l.raw_name().ok())
483 .map(|s| s.to_string()),
484 file: frame
485 .location
486 .as_ref()
487 .and_then(|l| l.file)
488 .map(|s| s.to_string()),
489 line: frame.location.as_ref().and_then(|l| l.line),
490 column: frame.location.as_ref().and_then(|l| l.column),
491 });
492 }
493 }
494 }
495 }
496
497 Some(FrameInfo {
498 module,
499 func_index,
500 func_name,
501 instr,
502 func_start,
503 symbols,
504 })
505 }
506
507 /// Returns the WebAssembly function index for this frame.
508 ///
509 /// This function index is the index in the function index space of the
510 /// WebAssembly module that this frame comes from.
511 pub fn func_index(&self) -> u32 {
512 self.func_index
513 }
514
515 /// Returns the module for this frame.
516 ///
517 /// This is the module who's code was being run in this frame.
518 pub fn module(&self) -> &Module {
519 &self.module
520 }
521
522 /// Returns a descriptive name of the function for this frame, if one is
523 /// available.
524 ///
525 /// The name of this function may come from the `name` section of the
526 /// WebAssembly binary, or wasmtime may try to infer a better name for it if
527 /// not available, for example the name of the export if it's exported.
528 ///
529 /// This return value is primarily used for debugging and human-readable
530 /// purposes for things like traps. Note that the exact return value may be
531 /// tweaked over time here and isn't guaranteed to be something in
532 /// particular about a wasm module due to its primary purpose of assisting
533 /// in debugging.
534 ///
535 /// This function returns `None` when no name could be inferred.
536 pub fn func_name(&self) -> Option<&str> {
537 self.func_name.as_deref()
538 }
539
540 /// Returns the offset within the original wasm module this frame's program
541 /// counter was at.
542 ///
543 /// The offset here is the offset from the beginning of the original wasm
544 /// module to the instruction that this frame points to.
545 ///
546 /// Note that `None` may be returned if the original module was not
547 /// compiled with mapping information to yield this information. This is
548 /// controlled by the
549 /// [`Config::generate_address_map`](crate::Config::generate_address_map)
550 /// configuration option.
551 pub fn module_offset(&self) -> Option<usize> {
552 Some(self.instr?.file_offset()? as usize)
553 }
554
555 /// Returns the offset from the original wasm module's function to this
556 /// frame's program counter.
557 ///
558 /// The offset here is the offset from the beginning of the defining
559 /// function of this frame (within the wasm module) to the instruction this
560 /// frame points to.
561 ///
562 /// Note that `None` may be returned if the original module was not
563 /// compiled with mapping information to yield this information. This is
564 /// controlled by the
565 /// [`Config::generate_address_map`](crate::Config::generate_address_map)
566 /// configuration option.
567 pub fn func_offset(&self) -> Option<usize> {
568 let instr_offset = self.instr?.file_offset()?;
569 Some((instr_offset - self.func_start.file_offset()?) as usize)
570 }
571
572 /// Returns the debug symbols found, if any, for this function frame.
573 ///
574 /// When a wasm program is compiled with DWARF debug information then this
575 /// function may be populated to return symbols which contain extra debug
576 /// information about a frame including the filename and line number. If no
577 /// debug information was found or if it was malformed then this will return
578 /// an empty array.
579 pub fn symbols(&self) -> &[FrameSymbol] {
580 &self.symbols
581 }
582}
583
584/// Debug information for a symbol that is attached to a [`FrameInfo`].
585///
586/// When DWARF debug information is present in a wasm file then this structure
587/// can be found on a [`FrameInfo`] and can be used to learn about filenames,
588/// line numbers, etc, which are the origin of a function in a stack trace.
589#[derive(Debug)]
590pub struct FrameSymbol {
591 name: Option<String>,
592 file: Option<String>,
593 line: Option<u32>,
594 column: Option<u32>,
595}
596
597impl FrameSymbol {
598 /// Returns the function name associated with this symbol.
599 ///
600 /// Note that this may not be present with malformed debug information, or
601 /// the debug information may not include it. Also note that the symbol is
602 /// frequently mangled, so you might need to run some form of demangling
603 /// over it.
604 pub fn name(&self) -> Option<&str> {
605 self.name.as_deref()
606 }
607
608 /// Returns the source code filename this symbol was defined in.
609 ///
610 /// Note that this may not be present with malformed debug information, or
611 /// the debug information may not include it.
612 pub fn file(&self) -> Option<&str> {
613 self.file.as_deref()
614 }
615
616 /// Returns the 1-indexed source code line number this symbol was defined
617 /// on.
618 ///
619 /// Note that this may not be present with malformed debug information, or
620 /// the debug information may not include it.
621 pub fn line(&self) -> Option<u32> {
622 self.line
623 }
624
625 /// Returns the 1-indexed source code column number this symbol was defined
626 /// on.
627 ///
628 /// Note that this may not be present with malformed debug information, or
629 /// the debug information may not include it.
630 pub fn column(&self) -> Option<u32> {
631 self.column
632 }
633}