dusk_wasmtime/runtime/trap.rs
1#[cfg(feature = "coredump")]
2use super::coredump::WasmCoreDump;
3use crate::store::StoreOpaque;
4use crate::{AsContext, Module};
5use anyhow::Error;
6use std::fmt;
7use wasmtime_environ::{
8 demangle_function_name, demangle_function_name_or_index, EntityRef, FilePos,
9};
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 [`anyhow`] crate
23/// where most results are a [`Result<T>`](anyhow::Result) which is an alias for
24/// [`Result<T, anyhow::Error>`](std::result::Result). Errors in Wasmtime are
25/// represented with [`anyhow::Error`] which acts as a container for any type of
26/// error in addition to optional context for this error. The "base" error or
27/// [`anyhow::Error::root_cause`] is a [`Trap`] whenever WebAssembly hits a
28/// trap, or otherwise it's whatever the host created the error with when
29/// returning an error for a host call.
30///
31/// Any error which happens while WebAssembly is executing will also, by
32/// default, capture a backtrace of the wasm frames while executing. This
33/// backtrace is represented with a [`WasmBacktrace`] instance and is attached
34/// to the [`anyhow::Error`] return value as a
35/// [`context`](anyhow::Error::context). Inspecting a [`WasmBacktrace`] can be
36/// done with the [`downcast_ref`](anyhow::Error::downcast_ref) function. For
37/// information on this see the [`WasmBacktrace`] documentation.
38///
39/// # Examples
40///
41/// ```
42/// # use wasmtime::*;
43/// # fn main() -> Result<()> {
44/// let engine = Engine::default();
45/// let module = Module::new(
46/// &engine,
47/// r#"
48/// (module
49/// (func (export "trap")
50/// unreachable)
51/// (func $overflow (export "overflow")
52/// call $overflow)
53/// )
54/// "#,
55/// )?;
56/// let mut store = Store::new(&engine, ());
57/// let instance = Instance::new(&mut store, &module, &[])?;
58///
59/// let trap = instance.get_typed_func::<(), ()>(&mut store, "trap")?;
60/// let error = trap.call(&mut store, ()).unwrap_err();
61/// assert_eq!(*error.downcast_ref::<Trap>().unwrap(), Trap::UnreachableCodeReached);
62/// assert!(error.root_cause().is::<Trap>());
63///
64/// let overflow = instance.get_typed_func::<(), ()>(&mut store, "overflow")?;
65/// let error = overflow.call(&mut store, ()).unwrap_err();
66/// assert_eq!(*error.downcast_ref::<Trap>().unwrap(), Trap::StackOverflow);
67/// # Ok(())
68/// # }
69/// ```
70pub use wasmtime_environ::Trap;
71
72// Same safety requirements and caveats as
73// `wasmtime_runtime::raise_user_trap`.
74pub(crate) unsafe fn raise(error: anyhow::Error) -> ! {
75 let needs_backtrace = error.downcast_ref::<WasmBacktrace>().is_none();
76 wasmtime_runtime::raise_user_trap(error, needs_backtrace)
77}
78
79#[cold] // traps are exceptional, this helps move handling off the main path
80pub(crate) fn from_runtime_box(
81 store: &mut StoreOpaque,
82 runtime_trap: Box<wasmtime_runtime::Trap>,
83) -> Error {
84 let wasmtime_runtime::Trap {
85 reason,
86 backtrace,
87 coredumpstack,
88 } = *runtime_trap;
89 let (mut error, pc) = match reason {
90 // For user-defined errors they're already an `anyhow::Error` so no
91 // conversion is really necessary here, but a `backtrace` may have
92 // been captured so it's attempted to get inserted here.
93 //
94 // If the error is actually a `Trap` then the backtrace is inserted
95 // directly into the `Trap` since there's storage there for it.
96 // Otherwise though this represents a host-defined error which isn't
97 // using a `Trap` but instead some other condition that was fatal to
98 // wasm itself. In that situation the backtrace is inserted as
99 // contextual information on error using `error.context(...)` to
100 // provide useful information to debug with for the embedder/caller,
101 // otherwise the information about what the wasm was doing when the
102 // error was generated would be lost.
103 wasmtime_runtime::TrapReason::User {
104 error,
105 needs_backtrace,
106 } => {
107 debug_assert!(
108 needs_backtrace == backtrace.is_some() || !store.engine().config().wasm_backtrace
109 );
110 (error, None)
111 }
112 wasmtime_runtime::TrapReason::Jit {
113 pc,
114 faulting_addr,
115 trap,
116 } => {
117 let mut err: Error = trap.into();
118
119 // If a fault address was present, for example with segfaults,
120 // then simultaneously assert that it's within a known linear memory
121 // and additionally translate it to a wasm-local address to be added
122 // as context to the error.
123 if let Some(fault) = faulting_addr.and_then(|addr| store.wasm_fault(pc, addr)) {
124 err = err.context(fault);
125 }
126 (err, Some(pc))
127 }
128 wasmtime_runtime::TrapReason::Wasm(trap_code) => (trap_code.into(), None),
129 };
130
131 if let Some(bt) = backtrace {
132 let bt = WasmBacktrace::from_captured(store, bt, pc);
133 if !bt.wasm_trace.is_empty() {
134 error = error.context(bt);
135 }
136 }
137
138 let _ = &coredumpstack;
139 #[cfg(feature = "coredump")]
140 if let Some(coredump) = coredumpstack {
141 let bt = WasmBacktrace::from_captured(store, coredump.bt, pc);
142 let cd = WasmCoreDump::new(store, bt);
143 error = error.context(cd);
144 }
145
146 error
147}
148
149/// Representation of a backtrace of function frames in a WebAssembly module for
150/// where an error happened.
151///
152/// This structure is attached to the [`anyhow::Error`] returned from many
153/// Wasmtime functions that execute WebAssembly such as [`Instance::new`] or
154/// [`Func::call`]. This can be acquired with the [`anyhow::Error::downcast`]
155/// family of methods to programmatically inspect the backtrace. Otherwise since
156/// it's part of the error returned this will get printed along with the rest of
157/// the error when the error is logged.
158///
159/// Capturing of wasm backtraces can be configured through the
160/// [`Config::wasm_backtrace`](crate::Config::wasm_backtrace) method.
161///
162/// For more information about errors in wasmtime see the documentation of the
163/// [`Trap`] type.
164///
165/// [`Func::call`]: crate::Func::call
166/// [`Instance::new`]: crate::Instance::new
167///
168/// # Examples
169///
170/// ```
171/// # use wasmtime::*;
172/// # fn main() -> Result<()> {
173/// let engine = Engine::default();
174/// let module = Module::new(
175/// &engine,
176/// r#"
177/// (module
178/// (func $start (export "run")
179/// call $trap)
180/// (func $trap
181/// unreachable)
182/// )
183/// "#,
184/// )?;
185/// let mut store = Store::new(&engine, ());
186/// let instance = Instance::new(&mut store, &module, &[])?;
187/// let func = instance.get_typed_func::<(), ()>(&mut store, "run")?;
188/// let error = func.call(&mut store, ()).unwrap_err();
189/// let bt = error.downcast_ref::<WasmBacktrace>().unwrap();
190/// let frames = bt.frames();
191/// assert_eq!(frames.len(), 2);
192/// assert_eq!(frames[0].func_name(), Some("trap"));
193/// assert_eq!(frames[1].func_name(), Some("start"));
194/// # Ok(())
195/// # }
196/// ```
197#[derive(Debug)]
198pub struct WasmBacktrace {
199 wasm_trace: Vec<FrameInfo>,
200 hint_wasm_backtrace_details_env: bool,
201 // This is currently only present for the `Debug` implementation for extra
202 // context.
203 #[allow(dead_code)]
204 runtime_trace: wasmtime_runtime::Backtrace,
205}
206
207impl WasmBacktrace {
208 /// Captures a trace of the WebAssembly frames on the stack for the
209 /// provided store.
210 ///
211 /// This will return a [`WasmBacktrace`] which holds captured
212 /// [`FrameInfo`]s for each frame of WebAssembly on the call stack of the
213 /// current thread. If no WebAssembly is on the stack then the returned
214 /// backtrace will have no frames in it.
215 ///
216 /// Note that this function will respect the [`Config::wasm_backtrace`]
217 /// configuration option and will return an empty backtrace if that is
218 /// disabled. To always capture a backtrace use the
219 /// [`WasmBacktrace::force_capture`] method.
220 ///
221 /// Also note that this function will only capture frames from the
222 /// specified `store` on the stack, ignoring frames from other stores if
223 /// present.
224 ///
225 /// [`Config::wasm_backtrace`]: crate::Config::wasm_backtrace
226 ///
227 /// # Example
228 ///
229 /// ```
230 /// # use wasmtime::*;
231 /// # fn main() -> Result<()> {
232 /// let engine = Engine::default();
233 /// let module = Module::new(
234 /// &engine,
235 /// r#"
236 /// (module
237 /// (import "" "" (func $host))
238 /// (func $foo (export "f") call $bar)
239 /// (func $bar call $host)
240 /// )
241 /// "#,
242 /// )?;
243 ///
244 /// let mut store = Store::new(&engine, ());
245 /// let func = Func::wrap(&mut store, |cx: Caller<'_, ()>| {
246 /// let trace = WasmBacktrace::capture(&cx);
247 /// println!("{trace:?}");
248 /// });
249 /// let instance = Instance::new(&mut store, &module, &[func.into()])?;
250 /// let func = instance.get_typed_func::<(), ()>(&mut store, "f")?;
251 /// func.call(&mut store, ())?;
252 /// # Ok(())
253 /// # }
254 /// ```
255 pub fn capture(store: impl AsContext) -> WasmBacktrace {
256 let store = store.as_context();
257 if store.engine().config().wasm_backtrace {
258 Self::force_capture(store)
259 } else {
260 WasmBacktrace {
261 wasm_trace: Vec::new(),
262 hint_wasm_backtrace_details_env: false,
263 runtime_trace: wasmtime_runtime::Backtrace::empty(),
264 }
265 }
266 }
267
268 /// Unconditionally captures a trace of the WebAssembly frames on the stack
269 /// for the provided store.
270 ///
271 /// Same as [`WasmBacktrace::capture`] except that it disregards the
272 /// [`Config::wasm_backtrace`](crate::Config::wasm_backtrace) setting and
273 /// always captures a backtrace.
274 pub fn force_capture(store: impl AsContext) -> WasmBacktrace {
275 let store = store.as_context();
276 Self::from_captured(
277 store.0,
278 wasmtime_runtime::Backtrace::new(store.0.runtime_limits()),
279 None,
280 )
281 }
282
283 fn from_captured(
284 store: &StoreOpaque,
285 runtime_trace: wasmtime_runtime::Backtrace,
286 trap_pc: Option<usize>,
287 ) -> Self {
288 let mut wasm_trace = Vec::<FrameInfo>::with_capacity(runtime_trace.frames().len());
289 let mut hint_wasm_backtrace_details_env = false;
290 let wasm_backtrace_details_env_used =
291 store.engine().config().wasm_backtrace_details_env_used;
292
293 for frame in runtime_trace.frames() {
294 debug_assert!(frame.pc() != 0);
295
296 // Note that we need to be careful about the pc we pass in
297 // here to lookup frame information. This program counter is
298 // used to translate back to an original source location in
299 // the origin wasm module. If this pc is the exact pc that
300 // the trap happened at, then we look up that pc precisely.
301 // Otherwise backtrace information typically points at the
302 // pc *after* the call instruction (because otherwise it's
303 // likely a call instruction on the stack). In that case we
304 // want to lookup information for the previous instruction
305 // (the call instruction) so we subtract one as the lookup.
306 let pc_to_lookup = if Some(frame.pc()) == trap_pc {
307 frame.pc()
308 } else {
309 frame.pc() - 1
310 };
311
312 // NB: The PC we are looking up _must_ be a Wasm PC since
313 // `wasmtime_runtime::Backtrace` only contains Wasm frames.
314 //
315 // However, consider the case where we have multiple, nested calls
316 // across stores (with host code in between, by necessity, since
317 // only things in the same store can be linked directly together):
318 //
319 // | ... |
320 // | Host | |
321 // +-----------------+ | stack
322 // | Wasm in store A | | grows
323 // +-----------------+ | down
324 // | Host | |
325 // +-----------------+ |
326 // | Wasm in store B | V
327 // +-----------------+
328 //
329 // In this scenario, the `wasmtime_runtime::Backtrace` will contain
330 // two frames: Wasm in store B followed by Wasm in store A. But
331 // `store.modules()` will only have the module information for
332 // modules instantiated within this store. Therefore, we use `if let
333 // Some(..)` instead of the `unwrap` you might otherwise expect and
334 // we ignore frames from modules that were not registered in this
335 // store's module registry.
336 if let Some((info, module)) = store.modules().lookup_frame_info(pc_to_lookup) {
337 wasm_trace.push(info);
338
339 // If this frame has unparsed debug information and the
340 // store's configuration indicates that we were
341 // respecting the environment variable of whether to
342 // do this then we will print out a helpful note in
343 // `Display` to indicate that more detailed information
344 // in a trap may be available.
345 let has_unparsed_debuginfo = module.compiled_module().has_unparsed_debuginfo();
346 if has_unparsed_debuginfo && wasm_backtrace_details_env_used {
347 hint_wasm_backtrace_details_env = true;
348 }
349 }
350 }
351
352 Self {
353 wasm_trace,
354 runtime_trace,
355 hint_wasm_backtrace_details_env,
356 }
357 }
358
359 /// Returns a list of function frames in WebAssembly this backtrace
360 /// represents.
361 pub fn frames(&self) -> &[FrameInfo] {
362 self.wasm_trace.as_slice()
363 }
364}
365
366impl fmt::Display for WasmBacktrace {
367 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
368 writeln!(f, "error while executing at wasm backtrace:")?;
369
370 let mut needs_newline = false;
371 for (i, frame) in self.wasm_trace.iter().enumerate() {
372 // Avoid putting a trailing newline on the output
373 if needs_newline {
374 writeln!(f, "")?;
375 } else {
376 needs_newline = true;
377 }
378 let name = frame.module().name().unwrap_or("<unknown>");
379 write!(f, " {:>3}: ", i)?;
380
381 if let Some(offset) = frame.module_offset() {
382 write!(f, "{:#6x} - ", offset)?;
383 }
384
385 let write_raw_func_name = |f: &mut fmt::Formatter<'_>| {
386 demangle_function_name_or_index(f, frame.func_name(), frame.func_index() as usize)
387 };
388 if frame.symbols().is_empty() {
389 write!(f, "{}!", name)?;
390 write_raw_func_name(f)?;
391 } else {
392 for (i, symbol) in frame.symbols().iter().enumerate() {
393 if i > 0 {
394 write!(f, " - ")?;
395 } else {
396 // ...
397 }
398 match symbol.name() {
399 Some(name) => demangle_function_name(f, name)?,
400 None if i == 0 => write_raw_func_name(f)?,
401 None => write!(f, "<inlined function>")?,
402 }
403 if let Some(file) = symbol.file() {
404 writeln!(f, "")?;
405 write!(f, " at {}", file)?;
406 if let Some(line) = symbol.line() {
407 write!(f, ":{}", line)?;
408 if let Some(col) = symbol.column() {
409 write!(f, ":{}", col)?;
410 }
411 }
412 }
413 }
414 }
415 }
416 if self.hint_wasm_backtrace_details_env {
417 write!(f, "\nnote: using the `WASMTIME_BACKTRACE_DETAILS=1` environment variable may show more debugging information")?;
418 }
419 Ok(())
420 }
421}
422
423/// Description of a frame in a backtrace for a [`WasmBacktrace`].
424///
425/// Whenever an error happens while WebAssembly is executing a
426/// [`WasmBacktrace`] will be attached to the error returned which can be used
427/// to acquire this `FrameInfo`. For more information see [`WasmBacktrace`].
428#[derive(Debug)]
429pub struct FrameInfo {
430 module: Module,
431 func_index: u32,
432 func_name: Option<String>,
433 func_start: FilePos,
434 instr: Option<FilePos>,
435 symbols: Vec<FrameSymbol>,
436}
437
438impl FrameInfo {
439 /// Fetches frame information about a program counter in a backtrace.
440 ///
441 /// Returns an object if this `pc` is known to this module, or returns `None`
442 /// if no information can be found.
443 pub(crate) fn new(module: Module, text_offset: usize) -> Option<FrameInfo> {
444 let compiled_module = module.compiled_module();
445 let (index, _func_offset) = compiled_module.func_by_text_offset(text_offset)?;
446 let info = compiled_module.wasm_func_info(index);
447 let func_start = info.start_srcloc;
448 let instr = wasmtime_environ::lookup_file_pos(
449 compiled_module.code_memory().address_map_data(),
450 text_offset,
451 );
452 let index = compiled_module.module().func_index(index);
453 let func_index = index.index() as u32;
454 let func_name = compiled_module.func_name(index).map(|s| s.to_string());
455
456 // In debug mode for now assert that we found a mapping for `pc` within
457 // the function, because otherwise something is buggy along the way and
458 // not accounting for all the instructions. This isn't super critical
459 // though so we can omit this check in release mode.
460 //
461 // Note that if the module doesn't even have an address map due to
462 // compilation settings then it's expected that `instr` is `None`.
463 debug_assert!(
464 instr.is_some() || !compiled_module.has_address_map(),
465 "failed to find instruction for {:#x}",
466 text_offset
467 );
468
469 // Use our wasm-relative pc to symbolize this frame. If there's a
470 // symbolication context (dwarf debug info) available then we can try to
471 // look this up there.
472 //
473 // Note that dwarf pcs are code-section-relative, hence the subtraction
474 // from the location of `instr`. Also note that all errors are ignored
475 // here for now since technically wasm modules can always have any
476 // custom section contents.
477 let mut symbols = Vec::new();
478
479 let _ = &mut symbols;
480 #[cfg(feature = "addr2line")]
481 if let Some(s) = &compiled_module.symbolize_context().ok().and_then(|c| c) {
482 if let Some(offset) = instr.and_then(|i| i.file_offset()) {
483 let to_lookup = u64::from(offset) - s.code_section_offset();
484 if let Ok(mut frames) = s.addr2line().find_frames(to_lookup).skip_all_loads() {
485 while let Ok(Some(frame)) = frames.next() {
486 symbols.push(FrameSymbol {
487 name: frame
488 .function
489 .as_ref()
490 .and_then(|l| l.raw_name().ok())
491 .map(|s| s.to_string()),
492 file: frame
493 .location
494 .as_ref()
495 .and_then(|l| l.file)
496 .map(|s| s.to_string()),
497 line: frame.location.as_ref().and_then(|l| l.line),
498 column: frame.location.as_ref().and_then(|l| l.column),
499 });
500 }
501 }
502 }
503 }
504
505 Some(FrameInfo {
506 module,
507 func_index,
508 func_name,
509 instr,
510 func_start,
511 symbols,
512 })
513 }
514
515 /// Returns the WebAssembly function index for this frame.
516 ///
517 /// This function index is the index in the function index space of the
518 /// WebAssembly module that this frame comes from.
519 pub fn func_index(&self) -> u32 {
520 self.func_index
521 }
522
523 /// Returns the module for this frame.
524 ///
525 /// This is the module who's code was being run in this frame.
526 pub fn module(&self) -> &Module {
527 &self.module
528 }
529
530 /// Returns a descriptive name of the function for this frame, if one is
531 /// available.
532 ///
533 /// The name of this function may come from the `name` section of the
534 /// WebAssembly binary, or wasmtime may try to infer a better name for it if
535 /// not available, for example the name of the export if it's exported.
536 ///
537 /// This return value is primarily used for debugging and human-readable
538 /// purposes for things like traps. Note that the exact return value may be
539 /// tweaked over time here and isn't guaranteed to be something in
540 /// particular about a wasm module due to its primary purpose of assisting
541 /// in debugging.
542 ///
543 /// This function returns `None` when no name could be inferred.
544 pub fn func_name(&self) -> Option<&str> {
545 self.func_name.as_deref()
546 }
547
548 /// Returns the offset within the original wasm module this frame's program
549 /// counter was at.
550 ///
551 /// The offset here is the offset from the beginning of the original wasm
552 /// module to the instruction that this frame points to.
553 ///
554 /// Note that `None` may be returned if the original module was not
555 /// compiled with mapping information to yield this information. This is
556 /// controlled by the
557 /// [`Config::generate_address_map`](crate::Config::generate_address_map)
558 /// configuration option.
559 pub fn module_offset(&self) -> Option<usize> {
560 Some(self.instr?.file_offset()? as usize)
561 }
562
563 /// Returns the offset from the original wasm module's function to this
564 /// frame's program counter.
565 ///
566 /// The offset here is the offset from the beginning of the defining
567 /// function of this frame (within the wasm module) to the instruction this
568 /// frame points to.
569 ///
570 /// Note that `None` may be returned if the original module was not
571 /// compiled with mapping information to yield this information. This is
572 /// controlled by the
573 /// [`Config::generate_address_map`](crate::Config::generate_address_map)
574 /// configuration option.
575 pub fn func_offset(&self) -> Option<usize> {
576 let instr_offset = self.instr?.file_offset()?;
577 Some((instr_offset - self.func_start.file_offset()?) as usize)
578 }
579
580 /// Returns the debug symbols found, if any, for this function frame.
581 ///
582 /// When a wasm program is compiled with DWARF debug information then this
583 /// function may be populated to return symbols which contain extra debug
584 /// information about a frame including the filename and line number. If no
585 /// debug information was found or if it was malformed then this will return
586 /// an empty array.
587 pub fn symbols(&self) -> &[FrameSymbol] {
588 &self.symbols
589 }
590}
591
592/// Debug information for a symbol that is attached to a [`FrameInfo`].
593///
594/// When DWARF debug information is present in a wasm file then this structure
595/// can be found on a [`FrameInfo`] and can be used to learn about filenames,
596/// line numbers, etc, which are the origin of a function in a stack trace.
597#[derive(Debug)]
598pub struct FrameSymbol {
599 name: Option<String>,
600 file: Option<String>,
601 line: Option<u32>,
602 column: Option<u32>,
603}
604
605impl FrameSymbol {
606 /// Returns the function name associated with this symbol.
607 ///
608 /// Note that this may not be present with malformed debug information, or
609 /// the debug information may not include it. Also note that the symbol is
610 /// frequently mangled, so you might need to run some form of demangling
611 /// over it.
612 pub fn name(&self) -> Option<&str> {
613 self.name.as_deref()
614 }
615
616 /// Returns the source code filename this symbol was defined in.
617 ///
618 /// Note that this may not be present with malformed debug information, or
619 /// the debug information may not include it.
620 pub fn file(&self) -> Option<&str> {
621 self.file.as_deref()
622 }
623
624 /// Returns the 1-indexed source code line number this symbol was defined
625 /// on.
626 ///
627 /// Note that this may not be present with malformed debug information, or
628 /// the debug information may not include it.
629 pub fn line(&self) -> Option<u32> {
630 self.line
631 }
632
633 /// Returns the 1-indexed source code column number this symbol was defined
634 /// on.
635 ///
636 /// Note that this may not be present with malformed debug information, or
637 /// the debug information may not include it.
638 pub fn column(&self) -> Option<u32> {
639 self.column
640 }
641}