1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639
#[cfg(feature = "coredump")]
use super::coredump::WasmCoreDump;
use crate::prelude::*;
use crate::store::StoreOpaque;
use crate::{AsContext, Module};
use core::fmt;
use wasmtime_environ::{demangle_function_name, demangle_function_name_or_index, FilePos};
/// Representation of a WebAssembly trap and what caused it to occur.
///
/// WebAssembly traps happen explicitly for instructions such as `unreachable`
/// but can also happen as side effects of other instructions such as `i32.load`
/// loading an out-of-bounds address. Traps halt the execution of WebAssembly
/// and cause an error to be returned to the host. This enumeration is a list of
/// all possible traps that can happen in wasm, in addition to some
/// Wasmtime-specific trap codes listed here as well.
///
/// # Errors in Wasmtime
///
/// Error-handling in Wasmtime is primarily done through the
/// [`anyhow`][mod@anyhow] crate where most results are a
/// [`Result<T>`](anyhow::Result) which is an alias for [`Result<T,
/// anyhow::Error>`](std::result::Result). Errors in Wasmtime are represented
/// with [`anyhow::Error`] which acts as a container for any type of error in
/// addition to optional context for this error. The "base" error or
/// [`anyhow::Error::root_cause`] is a [`Trap`] whenever WebAssembly hits a
/// trap, or otherwise it's whatever the host created the error with when
/// returning an error for a host call.
///
/// Any error which happens while WebAssembly is executing will also, by
/// default, capture a backtrace of the wasm frames while executing. This
/// backtrace is represented with a [`WasmBacktrace`] instance and is attached
/// to the [`anyhow::Error`] return value as a
/// [`context`](anyhow::Error::context). Inspecting a [`WasmBacktrace`] can be
/// done with the [`downcast_ref`](anyhow::Error::downcast_ref) function. For
/// information on this see the [`WasmBacktrace`] documentation.
///
/// # Examples
///
/// ```
/// # use wasmtime::*;
/// # fn main() -> Result<()> {
/// let engine = Engine::default();
/// let module = Module::new(
/// &engine,
/// r#"
/// (module
/// (func (export "trap")
/// unreachable)
/// (func $overflow (export "overflow")
/// call $overflow)
/// )
/// "#,
/// )?;
/// let mut store = Store::new(&engine, ());
/// let instance = Instance::new(&mut store, &module, &[])?;
///
/// let trap = instance.get_typed_func::<(), ()>(&mut store, "trap")?;
/// let error = trap.call(&mut store, ()).unwrap_err();
/// assert_eq!(*error.downcast_ref::<Trap>().unwrap(), Trap::UnreachableCodeReached);
/// assert!(error.root_cause().is::<Trap>());
///
/// let overflow = instance.get_typed_func::<(), ()>(&mut store, "overflow")?;
/// let error = overflow.call(&mut store, ()).unwrap_err();
/// assert_eq!(*error.downcast_ref::<Trap>().unwrap(), Trap::StackOverflow);
/// # Ok(())
/// # }
/// ```
pub use wasmtime_environ::Trap;
// Same safety requirements and caveats as
// `crate::runtime::vm::raise_user_trap`.
pub(crate) unsafe fn raise(error: anyhow::Error) -> ! {
let needs_backtrace = error.downcast_ref::<WasmBacktrace>().is_none();
crate::runtime::vm::raise_user_trap(error, needs_backtrace)
}
#[cold] // traps are exceptional, this helps move handling off the main path
pub(crate) fn from_runtime_box(
store: &mut StoreOpaque,
runtime_trap: Box<crate::runtime::vm::Trap>,
) -> Error {
let crate::runtime::vm::Trap {
reason,
backtrace,
coredumpstack,
} = *runtime_trap;
let (mut error, pc) = match reason {
// For user-defined errors they're already an `anyhow::Error` so no
// conversion is really necessary here, but a `backtrace` may have
// been captured so it's attempted to get inserted here.
//
// If the error is actually a `Trap` then the backtrace is inserted
// directly into the `Trap` since there's storage there for it.
// Otherwise though this represents a host-defined error which isn't
// using a `Trap` but instead some other condition that was fatal to
// wasm itself. In that situation the backtrace is inserted as
// contextual information on error using `error.context(...)` to
// provide useful information to debug with for the embedder/caller,
// otherwise the information about what the wasm was doing when the
// error was generated would be lost.
crate::runtime::vm::TrapReason::User {
error,
needs_backtrace,
} => {
debug_assert!(
needs_backtrace == backtrace.is_some() || !store.engine().config().wasm_backtrace
);
(error, None)
}
crate::runtime::vm::TrapReason::Jit {
pc,
faulting_addr,
trap,
} => {
let mut err: Error = trap.into_anyhow();
// If a fault address was present, for example with segfaults,
// then simultaneously assert that it's within a known linear memory
// and additionally translate it to a wasm-local address to be added
// as context to the error.
if let Some(fault) = faulting_addr.and_then(|addr| store.wasm_fault(pc, addr)) {
err = err.context(fault);
}
(err, Some(pc))
}
crate::runtime::vm::TrapReason::Wasm(trap_code) => (trap_code.into_anyhow(), None),
};
if let Some(bt) = backtrace {
let bt = WasmBacktrace::from_captured(store, bt, pc);
if !bt.wasm_trace.is_empty() {
error = error.context(bt);
}
}
let _ = &coredumpstack;
#[cfg(feature = "coredump")]
if let Some(coredump) = coredumpstack {
let bt = WasmBacktrace::from_captured(store, coredump.bt, pc);
let cd = WasmCoreDump::new(store, bt);
error = error.context(cd);
}
error
}
/// Representation of a backtrace of function frames in a WebAssembly module for
/// where an error happened.
///
/// This structure is attached to the [`anyhow::Error`] returned from many
/// Wasmtime functions that execute WebAssembly such as [`Instance::new`] or
/// [`Func::call`]. This can be acquired with the [`anyhow::Error::downcast`]
/// family of methods to programmatically inspect the backtrace. Otherwise since
/// it's part of the error returned this will get printed along with the rest of
/// the error when the error is logged.
///
/// Capturing of wasm backtraces can be configured through the
/// [`Config::wasm_backtrace`](crate::Config::wasm_backtrace) method.
///
/// For more information about errors in wasmtime see the documentation of the
/// [`Trap`] type.
///
/// [`Func::call`]: crate::Func::call
/// [`Instance::new`]: crate::Instance::new
///
/// # Examples
///
/// ```
/// # use wasmtime::*;
/// # fn main() -> Result<()> {
/// let engine = Engine::default();
/// let module = Module::new(
/// &engine,
/// r#"
/// (module
/// (func $start (export "run")
/// call $trap)
/// (func $trap
/// unreachable)
/// )
/// "#,
/// )?;
/// let mut store = Store::new(&engine, ());
/// let instance = Instance::new(&mut store, &module, &[])?;
/// let func = instance.get_typed_func::<(), ()>(&mut store, "run")?;
/// let error = func.call(&mut store, ()).unwrap_err();
/// let bt = error.downcast_ref::<WasmBacktrace>().unwrap();
/// let frames = bt.frames();
/// assert_eq!(frames.len(), 2);
/// assert_eq!(frames[0].func_name(), Some("trap"));
/// assert_eq!(frames[1].func_name(), Some("start"));
/// # Ok(())
/// # }
/// ```
#[derive(Debug)]
pub struct WasmBacktrace {
wasm_trace: Vec<FrameInfo>,
hint_wasm_backtrace_details_env: bool,
// This is currently only present for the `Debug` implementation for extra
// context.
#[allow(dead_code)]
runtime_trace: crate::runtime::vm::Backtrace,
}
impl WasmBacktrace {
/// Captures a trace of the WebAssembly frames on the stack for the
/// provided store.
///
/// This will return a [`WasmBacktrace`] which holds captured
/// [`FrameInfo`]s for each frame of WebAssembly on the call stack of the
/// current thread. If no WebAssembly is on the stack then the returned
/// backtrace will have no frames in it.
///
/// Note that this function will respect the [`Config::wasm_backtrace`]
/// configuration option and will return an empty backtrace if that is
/// disabled. To always capture a backtrace use the
/// [`WasmBacktrace::force_capture`] method.
///
/// Also note that this function will only capture frames from the
/// specified `store` on the stack, ignoring frames from other stores if
/// present.
///
/// [`Config::wasm_backtrace`]: crate::Config::wasm_backtrace
///
/// # Example
///
/// ```
/// # use wasmtime::*;
/// # fn main() -> Result<()> {
/// let engine = Engine::default();
/// let module = Module::new(
/// &engine,
/// r#"
/// (module
/// (import "" "" (func $host))
/// (func $foo (export "f") call $bar)
/// (func $bar call $host)
/// )
/// "#,
/// )?;
///
/// let mut store = Store::new(&engine, ());
/// let func = Func::wrap(&mut store, |cx: Caller<'_, ()>| {
/// let trace = WasmBacktrace::capture(&cx);
/// println!("{trace:?}");
/// });
/// let instance = Instance::new(&mut store, &module, &[func.into()])?;
/// let func = instance.get_typed_func::<(), ()>(&mut store, "f")?;
/// func.call(&mut store, ())?;
/// # Ok(())
/// # }
/// ```
pub fn capture(store: impl AsContext) -> WasmBacktrace {
let store = store.as_context();
if store.engine().config().wasm_backtrace {
Self::force_capture(store)
} else {
WasmBacktrace {
wasm_trace: Vec::new(),
hint_wasm_backtrace_details_env: false,
runtime_trace: crate::runtime::vm::Backtrace::empty(),
}
}
}
/// Unconditionally captures a trace of the WebAssembly frames on the stack
/// for the provided store.
///
/// Same as [`WasmBacktrace::capture`] except that it disregards the
/// [`Config::wasm_backtrace`](crate::Config::wasm_backtrace) setting and
/// always captures a backtrace.
pub fn force_capture(store: impl AsContext) -> WasmBacktrace {
let store = store.as_context();
Self::from_captured(
store.0,
crate::runtime::vm::Backtrace::new(store.0.runtime_limits()),
None,
)
}
fn from_captured(
store: &StoreOpaque,
runtime_trace: crate::runtime::vm::Backtrace,
trap_pc: Option<usize>,
) -> Self {
let mut wasm_trace = Vec::<FrameInfo>::with_capacity(runtime_trace.frames().len());
let mut hint_wasm_backtrace_details_env = false;
let wasm_backtrace_details_env_used =
store.engine().config().wasm_backtrace_details_env_used;
for frame in runtime_trace.frames() {
debug_assert!(frame.pc() != 0);
// Note that we need to be careful about the pc we pass in
// here to lookup frame information. This program counter is
// used to translate back to an original source location in
// the origin wasm module. If this pc is the exact pc that
// the trap happened at, then we look up that pc precisely.
// Otherwise backtrace information typically points at the
// pc *after* the call instruction (because otherwise it's
// likely a call instruction on the stack). In that case we
// want to lookup information for the previous instruction
// (the call instruction) so we subtract one as the lookup.
let pc_to_lookup = if Some(frame.pc()) == trap_pc {
frame.pc()
} else {
frame.pc() - 1
};
// NB: The PC we are looking up _must_ be a Wasm PC since
// `crate::runtime::vm::Backtrace` only contains Wasm frames.
//
// However, consider the case where we have multiple, nested calls
// across stores (with host code in between, by necessity, since
// only things in the same store can be linked directly together):
//
// | ... |
// | Host | |
// +-----------------+ | stack
// | Wasm in store A | | grows
// +-----------------+ | down
// | Host | |
// +-----------------+ |
// | Wasm in store B | V
// +-----------------+
//
// In this scenario, the `crate::runtime::vm::Backtrace` will
// contain two frames: Wasm in store B followed by Wasm in store
// A. But `store.modules()` will only have the module information
// for modules instantiated within this store. Therefore, we use `if
// let Some(..)` instead of the `unwrap` you might otherwise expect
// and we ignore frames from modules that were not registered in
// this store's module registry.
if let Some((info, module)) = store.modules().lookup_frame_info(pc_to_lookup) {
wasm_trace.push(info);
// If this frame has unparsed debug information and the
// store's configuration indicates that we were
// respecting the environment variable of whether to
// do this then we will print out a helpful note in
// `Display` to indicate that more detailed information
// in a trap may be available.
let has_unparsed_debuginfo = module.compiled_module().has_unparsed_debuginfo();
if has_unparsed_debuginfo && wasm_backtrace_details_env_used {
hint_wasm_backtrace_details_env = true;
}
}
}
Self {
wasm_trace,
runtime_trace,
hint_wasm_backtrace_details_env,
}
}
/// Returns a list of function frames in WebAssembly this backtrace
/// represents.
pub fn frames(&self) -> &[FrameInfo] {
self.wasm_trace.as_slice()
}
}
impl fmt::Display for WasmBacktrace {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
writeln!(f, "error while executing at wasm backtrace:")?;
let mut needs_newline = false;
for (i, frame) in self.wasm_trace.iter().enumerate() {
// Avoid putting a trailing newline on the output
if needs_newline {
writeln!(f, "")?;
} else {
needs_newline = true;
}
let name = frame.module().name().unwrap_or("<unknown>");
write!(f, " {i:>3}: ")?;
if let Some(offset) = frame.module_offset() {
write!(f, "{offset:#6x} - ")?;
}
let write_raw_func_name = |f: &mut fmt::Formatter<'_>| {
demangle_function_name_or_index(f, frame.func_name(), frame.func_index() as usize)
};
if frame.symbols().is_empty() {
write!(f, "{name}!")?;
write_raw_func_name(f)?;
} else {
for (i, symbol) in frame.symbols().iter().enumerate() {
if i > 0 {
write!(f, " - ")?;
} else {
// ...
}
match symbol.name() {
Some(name) => demangle_function_name(f, name)?,
None if i == 0 => write_raw_func_name(f)?,
None => write!(f, "<inlined function>")?,
}
if let Some(file) = symbol.file() {
writeln!(f, "")?;
write!(f, " at {file}")?;
if let Some(line) = symbol.line() {
write!(f, ":{line}")?;
if let Some(col) = symbol.column() {
write!(f, ":{col}")?;
}
}
}
}
}
}
if self.hint_wasm_backtrace_details_env {
write!(f, "\nnote: using the `WASMTIME_BACKTRACE_DETAILS=1` environment variable may show more debugging information")?;
}
Ok(())
}
}
/// Description of a frame in a backtrace for a [`WasmBacktrace`].
///
/// Whenever an error happens while WebAssembly is executing a
/// [`WasmBacktrace`] will be attached to the error returned which can be used
/// to acquire this `FrameInfo`. For more information see [`WasmBacktrace`].
#[derive(Debug)]
pub struct FrameInfo {
module: Module,
func_index: u32,
func_name: Option<String>,
func_start: FilePos,
instr: Option<FilePos>,
symbols: Vec<FrameSymbol>,
}
impl FrameInfo {
/// Fetches frame information about a program counter in a backtrace.
///
/// Returns an object if this `pc` is known to this module, or returns `None`
/// if no information can be found.
pub(crate) fn new(module: Module, text_offset: usize) -> Option<FrameInfo> {
let compiled_module = module.compiled_module();
let (index, _func_offset) = compiled_module.func_by_text_offset(text_offset)?;
let info = compiled_module.wasm_func_info(index);
let func_start = info.start_srcloc;
let instr = wasmtime_environ::lookup_file_pos(
compiled_module.code_memory().address_map_data(),
text_offset,
);
let index = compiled_module.module().func_index(index);
let func_index = index.as_u32();
let func_name = compiled_module.func_name(index).map(|s| s.to_string());
// In debug mode for now assert that we found a mapping for `pc` within
// the function, because otherwise something is buggy along the way and
// not accounting for all the instructions. This isn't super critical
// though so we can omit this check in release mode.
//
// Note that if the module doesn't even have an address map due to
// compilation settings then it's expected that `instr` is `None`.
debug_assert!(
instr.is_some() || !compiled_module.has_address_map(),
"failed to find instruction for {text_offset:#x}"
);
// Use our wasm-relative pc to symbolize this frame. If there's a
// symbolication context (dwarf debug info) available then we can try to
// look this up there.
//
// Note that dwarf pcs are code-section-relative, hence the subtraction
// from the location of `instr`. Also note that all errors are ignored
// here for now since technically wasm modules can always have any
// custom section contents.
let mut symbols = Vec::new();
let _ = &mut symbols;
#[cfg(feature = "addr2line")]
if let Some(s) = &compiled_module.symbolize_context().ok().and_then(|c| c) {
if let Some(offset) = instr.and_then(|i| i.file_offset()) {
let to_lookup = u64::from(offset) - s.code_section_offset();
if let Ok(mut frames) = s.addr2line().find_frames(to_lookup).skip_all_loads() {
while let Ok(Some(frame)) = frames.next() {
symbols.push(FrameSymbol {
name: frame
.function
.as_ref()
.and_then(|l| l.raw_name().ok())
.map(|s| s.to_string()),
file: frame
.location
.as_ref()
.and_then(|l| l.file)
.map(|s| s.to_string()),
line: frame.location.as_ref().and_then(|l| l.line),
column: frame.location.as_ref().and_then(|l| l.column),
});
}
}
}
}
Some(FrameInfo {
module,
func_index,
func_name,
instr,
func_start,
symbols,
})
}
/// Returns the WebAssembly function index for this frame.
///
/// This function index is the index in the function index space of the
/// WebAssembly module that this frame comes from.
pub fn func_index(&self) -> u32 {
self.func_index
}
/// Returns the module for this frame.
///
/// This is the module who's code was being run in this frame.
pub fn module(&self) -> &Module {
&self.module
}
/// Returns a descriptive name of the function for this frame, if one is
/// available.
///
/// The name of this function may come from the `name` section of the
/// WebAssembly binary, or wasmtime may try to infer a better name for it if
/// not available, for example the name of the export if it's exported.
///
/// This return value is primarily used for debugging and human-readable
/// purposes for things like traps. Note that the exact return value may be
/// tweaked over time here and isn't guaranteed to be something in
/// particular about a wasm module due to its primary purpose of assisting
/// in debugging.
///
/// This function returns `None` when no name could be inferred.
pub fn func_name(&self) -> Option<&str> {
self.func_name.as_deref()
}
/// Returns the offset within the original wasm module this frame's program
/// counter was at.
///
/// The offset here is the offset from the beginning of the original wasm
/// module to the instruction that this frame points to.
///
/// Note that `None` may be returned if the original module was not
/// compiled with mapping information to yield this information. This is
/// controlled by the
/// [`Config::generate_address_map`](crate::Config::generate_address_map)
/// configuration option.
pub fn module_offset(&self) -> Option<usize> {
Some(self.instr?.file_offset()? as usize)
}
/// Returns the offset from the original wasm module's function to this
/// frame's program counter.
///
/// The offset here is the offset from the beginning of the defining
/// function of this frame (within the wasm module) to the instruction this
/// frame points to.
///
/// Note that `None` may be returned if the original module was not
/// compiled with mapping information to yield this information. This is
/// controlled by the
/// [`Config::generate_address_map`](crate::Config::generate_address_map)
/// configuration option.
pub fn func_offset(&self) -> Option<usize> {
let instr_offset = self.instr?.file_offset()?;
Some((instr_offset - self.func_start.file_offset()?) as usize)
}
/// Returns the debug symbols found, if any, for this function frame.
///
/// When a wasm program is compiled with DWARF debug information then this
/// function may be populated to return symbols which contain extra debug
/// information about a frame including the filename and line number. If no
/// debug information was found or if it was malformed then this will return
/// an empty array.
pub fn symbols(&self) -> &[FrameSymbol] {
&self.symbols
}
}
/// Debug information for a symbol that is attached to a [`FrameInfo`].
///
/// When DWARF debug information is present in a wasm file then this structure
/// can be found on a [`FrameInfo`] and can be used to learn about filenames,
/// line numbers, etc, which are the origin of a function in a stack trace.
#[derive(Debug)]
pub struct FrameSymbol {
name: Option<String>,
file: Option<String>,
line: Option<u32>,
column: Option<u32>,
}
impl FrameSymbol {
/// Returns the function name associated with this symbol.
///
/// Note that this may not be present with malformed debug information, or
/// the debug information may not include it. Also note that the symbol is
/// frequently mangled, so you might need to run some form of demangling
/// over it.
pub fn name(&self) -> Option<&str> {
self.name.as_deref()
}
/// Returns the source code filename this symbol was defined in.
///
/// Note that this may not be present with malformed debug information, or
/// the debug information may not include it.
pub fn file(&self) -> Option<&str> {
self.file.as_deref()
}
/// Returns the 1-indexed source code line number this symbol was defined
/// on.
///
/// Note that this may not be present with malformed debug information, or
/// the debug information may not include it.
pub fn line(&self) -> Option<u32> {
self.line
}
/// Returns the 1-indexed source code column number this symbol was defined
/// on.
///
/// Note that this may not be present with malformed debug information, or
/// the debug information may not include it.
pub fn column(&self) -> Option<u32> {
self.column
}
}