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
//! Support for capturing a stack backtrace of an OS thread
//!
//! This module contains the support necessary to capture a stack backtrace of a
//! running OS thread from the OS thread itself. The `Backtrace` type supports
//! capturing a stack trace via the `Backtrace::capture` and
//! `Backtrace::force_capture` functions.
//!
//! A backtrace is typically quite handy to attach to errors (e.g. types
//! implementing `std::error::Error`) to get a causal chain of where an error
//! was generated.
//!
//! ## Accuracy
//!
//! Backtraces are attempted to be as accurate as possible, but no guarantees
//! are provided about the exact accuracy of a backtrace. Instruction pointers,
//! symbol names, filenames, line numbers, etc, may all be incorrect when
//! reported. Accuracy is attempted on a best-effort basis, however, any bug
//! reports are always welcome to indicate areas of improvement!
//!
//! For most platforms a backtrace with a filename/line number requires that
//! programs be compiled with debug information. Without debug information
//! filenames/line numbers will not be reported.
//!
//! ## Platform support
//!
//! Not all platforms that std compiles for support capturing backtraces. Some
//! platforms simply do nothing when capturing a backtrace. To check whether the
//! platform supports capturing backtraces you can consult the `BacktraceStatus`
//! enum as a result of `Backtrace::status`.
//!
//! Like above with accuracy platform support is done on a best effort basis.
//! Sometimes libraries might not be available at runtime or something may go
//! wrong which would cause a backtrace to not be captured. Please feel free to
//! report issues with platforms where a backtrace cannot be captured though!
//!
//! ## Environment Variables
//!
//! The `Backtrace::capture` function might not actually capture a backtrace by
//! default. Its behavior is governed by two environment variables:
//!
//! * `RUST_LIB_BACKTRACE` - if this is set to `0` then `Backtrace::capture`
//! will never capture a backtrace. Any other value set will enable
//! `Backtrace::capture`.
//!
//! * `RUST_BACKTRACE` - if `RUST_LIB_BACKTRACE` is not set, then this variable
//! is consulted with the same rules of `RUST_LIB_BACKTRACE`.
//!
//! * If neither of the above env vars are set, then `Backtrace::capture` will
//! be disabled.
//!
//! Capturing a backtrace can be a quite expensive runtime operation, so the
//! environment variables allow either forcibly disabling this runtime
//! performance hit or allow selectively enabling it in some programs.
//!
//! Note that the `Backtrace::force_capture` function can be used to ignore
//! these environment variables. Also note that the state of environment
//! variables is cached once the first backtrace is created, so altering
//! `RUST_LIB_BACKTRACE` or `RUST_BACKTRACE` at runtime might not actually change
//! how backtraces are captured.
#![stable(feature = "backtrace", since = "1.65.0")]
#[cfg(test)]
mod tests;
// NB: A note on resolution of a backtrace:
//
// Backtraces primarily happen in two steps, one is where we actually capture
// the stack backtrace, giving us a list of instruction pointers corresponding
// to stack frames. Next we take these instruction pointers and, one-by-one,
// turn them into a human readable name (like `main`).
//
// The first phase can be somewhat expensive (walking the stack), especially
// on MSVC where debug information is consulted to return inline frames each as
// their own frame. The second phase, however, is almost always extremely
// expensive (on the order of milliseconds sometimes) when it's consulting debug
// information.
//
// We attempt to amortize this cost as much as possible by delaying resolution
// of an address to a human readable name for as long as possible. When
// `Backtrace::create` is called to capture a backtrace it doesn't actually
// perform any symbol resolution, but rather we lazily resolve symbols only just
// before they're needed for printing. This way we can make capturing a
// backtrace and throwing it away much cheaper, but actually printing a
// backtrace is still basically the same cost.
//
// This strategy comes at the cost of some synchronization required inside of a
// `Backtrace`, but that's a relatively small price to pay relative to capturing
// a backtrace or actually symbolizing it.
use crate::backtrace_rs::{self, BytesOrWideString};
use crate::env;
use crate::ffi::c_void;
use crate::fmt;
use crate::panic::UnwindSafe;
use crate::sync::atomic::{AtomicU8, Ordering::Relaxed};
use crate::sync::LazyLock;
use crate::sys_common::backtrace::{lock, output_filename, set_image_base};
/// A captured OS thread stack backtrace.
///
/// This type represents a stack backtrace for an OS thread captured at a
/// previous point in time. In some instances the `Backtrace` type may
/// internally be empty due to configuration. For more information see
/// `Backtrace::capture`.
#[stable(feature = "backtrace", since = "1.65.0")]
#[must_use]
pub struct Backtrace {
inner: Inner,
}
/// The current status of a backtrace, indicating whether it was captured or
/// whether it is empty for some other reason.
#[stable(feature = "backtrace", since = "1.65.0")]
#[non_exhaustive]
#[derive(Debug, PartialEq, Eq)]
pub enum BacktraceStatus {
/// Capturing a backtrace is not supported, likely because it's not
/// implemented for the current platform.
#[stable(feature = "backtrace", since = "1.65.0")]
Unsupported,
/// Capturing a backtrace has been disabled through either the
/// `RUST_LIB_BACKTRACE` or `RUST_BACKTRACE` environment variables.
#[stable(feature = "backtrace", since = "1.65.0")]
Disabled,
/// A backtrace has been captured and the `Backtrace` should print
/// reasonable information when rendered.
#[stable(feature = "backtrace", since = "1.65.0")]
Captured,
}
enum Inner {
Unsupported,
Disabled,
Captured(LazyLock<Capture, LazyResolve>),
}
struct Capture {
actual_start: usize,
frames: Vec<BacktraceFrame>,
}
fn _assert_send_sync() {
fn _assert<T: Send + Sync>() {}
_assert::<Backtrace>();
}
/// A single frame of a backtrace.
#[unstable(feature = "backtrace_frames", issue = "79676")]
pub struct BacktraceFrame {
frame: RawFrame,
symbols: Vec<BacktraceSymbol>,
}
#[derive(Debug)]
enum RawFrame {
Actual(backtrace_rs::Frame),
#[cfg(test)]
Fake,
}
struct BacktraceSymbol {
name: Option<Vec<u8>>,
filename: Option<BytesOrWide>,
lineno: Option<u32>,
colno: Option<u32>,
}
enum BytesOrWide {
Bytes(Vec<u8>),
Wide(Vec<u16>),
}
#[stable(feature = "backtrace", since = "1.65.0")]
impl fmt::Debug for Backtrace {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
let capture = match &self.inner {
Inner::Unsupported => return fmt.write_str("<unsupported>"),
Inner::Disabled => return fmt.write_str("<disabled>"),
Inner::Captured(c) => &**c,
};
let frames = &capture.frames[capture.actual_start..];
write!(fmt, "Backtrace ")?;
let mut dbg = fmt.debug_list();
for frame in frames {
if frame.frame.ip().is_null() {
continue;
}
dbg.entries(&frame.symbols);
}
dbg.finish()
}
}
#[unstable(feature = "backtrace_frames", issue = "79676")]
impl fmt::Debug for BacktraceFrame {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
let mut dbg = fmt.debug_list();
dbg.entries(&self.symbols);
dbg.finish()
}
}
impl fmt::Debug for BacktraceSymbol {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
// FIXME: improve formatting: https://github.com/rust-lang/rust/issues/65280
// FIXME: Also, include column numbers into the debug format as Display already has them.
// Until there are stable per-frame accessors, the format shouldn't be changed:
// https://github.com/rust-lang/rust/issues/65280#issuecomment-638966585
write!(fmt, "{{ ")?;
if let Some(fn_name) = self.name.as_ref().map(|b| backtrace_rs::SymbolName::new(b)) {
write!(fmt, "fn: \"{:#}\"", fn_name)?;
} else {
write!(fmt, "fn: <unknown>")?;
}
if let Some(fname) = self.filename.as_ref() {
write!(fmt, ", file: \"{:?}\"", fname)?;
}
if let Some(line) = self.lineno {
write!(fmt, ", line: {:?}", line)?;
}
write!(fmt, " }}")
}
}
impl fmt::Debug for BytesOrWide {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
output_filename(
fmt,
match self {
BytesOrWide::Bytes(w) => BytesOrWideString::Bytes(w),
BytesOrWide::Wide(w) => BytesOrWideString::Wide(w),
},
backtrace_rs::PrintFmt::Short,
crate::env::current_dir().as_ref().ok(),
)
}
}
impl Backtrace {
/// Returns whether backtrace captures are enabled through environment
/// variables.
fn enabled() -> bool {
// Cache the result of reading the environment variables to make
// backtrace captures speedy, because otherwise reading environment
// variables every time can be somewhat slow.
static ENABLED: AtomicU8 = AtomicU8::new(0);
match ENABLED.load(Relaxed) {
0 => {}
1 => return false,
_ => return true,
}
let enabled = match env::var("RUST_LIB_BACKTRACE") {
Ok(s) => s != "0",
Err(_) => match env::var("RUST_BACKTRACE") {
Ok(s) => s != "0",
Err(_) => false,
},
};
ENABLED.store(enabled as u8 + 1, Relaxed);
enabled
}
/// Capture a stack backtrace of the current thread.
///
/// This function will capture a stack backtrace of the current OS thread of
/// execution, returning a `Backtrace` type which can be later used to print
/// the entire stack trace or render it to a string.
///
/// This function will be a noop if the `RUST_BACKTRACE` or
/// `RUST_LIB_BACKTRACE` backtrace variables are both not set. If either
/// environment variable is set and enabled then this function will actually
/// capture a backtrace. Capturing a backtrace can be both memory intensive
/// and slow, so these environment variables allow liberally using
/// `Backtrace::capture` and only incurring a slowdown when the environment
/// variables are set.
///
/// To forcibly capture a backtrace regardless of environment variables, use
/// the `Backtrace::force_capture` function.
#[stable(feature = "backtrace", since = "1.65.0")]
#[inline(never)] // want to make sure there's a frame here to remove
pub fn capture() -> Backtrace {
if !Backtrace::enabled() {
return Backtrace { inner: Inner::Disabled };
}
Backtrace::create(Backtrace::capture as usize)
}
/// Forcibly captures a full backtrace, regardless of environment variable
/// configuration.
///
/// This function behaves the same as `capture` except that it ignores the
/// values of the `RUST_BACKTRACE` and `RUST_LIB_BACKTRACE` environment
/// variables, always capturing a backtrace.
///
/// Note that capturing a backtrace can be an expensive operation on some
/// platforms, so this should be used with caution in performance-sensitive
/// parts of code.
#[stable(feature = "backtrace", since = "1.65.0")]
#[inline(never)] // want to make sure there's a frame here to remove
pub fn force_capture() -> Backtrace {
Backtrace::create(Backtrace::force_capture as usize)
}
/// Forcibly captures a disabled backtrace, regardless of environment
/// variable configuration.
#[stable(feature = "backtrace", since = "1.65.0")]
#[rustc_const_stable(feature = "backtrace", since = "1.65.0")]
pub const fn disabled() -> Backtrace {
Backtrace { inner: Inner::Disabled }
}
// Capture a backtrace which start just before the function addressed by
// `ip`
fn create(ip: usize) -> Backtrace {
let _lock = lock();
let mut frames = Vec::new();
let mut actual_start = None;
set_image_base();
unsafe {
backtrace_rs::trace_unsynchronized(|frame| {
frames.push(BacktraceFrame {
frame: RawFrame::Actual(frame.clone()),
symbols: Vec::new(),
});
if frame.symbol_address().addr() == ip && actual_start.is_none() {
actual_start = Some(frames.len());
}
true
});
}
// If no frames came out assume that this is an unsupported platform
// since `backtrace` doesn't provide a way of learning this right now,
// and this should be a good enough approximation.
let inner = if frames.is_empty() {
Inner::Unsupported
} else {
Inner::Captured(LazyLock::new(lazy_resolve(Capture {
actual_start: actual_start.unwrap_or(0),
frames,
})))
};
Backtrace { inner }
}
/// Returns the status of this backtrace, indicating whether this backtrace
/// request was unsupported, disabled, or a stack trace was actually
/// captured.
#[stable(feature = "backtrace", since = "1.65.0")]
#[must_use]
pub fn status(&self) -> BacktraceStatus {
match self.inner {
Inner::Unsupported => BacktraceStatus::Unsupported,
Inner::Disabled => BacktraceStatus::Disabled,
Inner::Captured(_) => BacktraceStatus::Captured,
}
}
}
impl<'a> Backtrace {
/// Returns an iterator over the backtrace frames.
#[must_use]
#[unstable(feature = "backtrace_frames", issue = "79676")]
pub fn frames(&'a self) -> &'a [BacktraceFrame] {
if let Inner::Captured(c) = &self.inner { &c.frames } else { &[] }
}
}
#[stable(feature = "backtrace", since = "1.65.0")]
impl fmt::Display for Backtrace {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
let capture = match &self.inner {
Inner::Unsupported => return fmt.write_str("unsupported backtrace"),
Inner::Disabled => return fmt.write_str("disabled backtrace"),
Inner::Captured(c) => &**c,
};
let full = fmt.alternate();
let (frames, style) = if full {
(&capture.frames[..], backtrace_rs::PrintFmt::Full)
} else {
(&capture.frames[capture.actual_start..], backtrace_rs::PrintFmt::Short)
};
// When printing paths we try to strip the cwd if it exists, otherwise
// we just print the path as-is. Note that we also only do this for the
// short format, because if it's full we presumably want to print
// everything.
let cwd = crate::env::current_dir();
let mut print_path = move |fmt: &mut fmt::Formatter<'_>, path: BytesOrWideString<'_>| {
output_filename(fmt, path, style, cwd.as_ref().ok())
};
let mut f = backtrace_rs::BacktraceFmt::new(fmt, style, &mut print_path);
f.add_context()?;
for frame in frames {
if frame.symbols.is_empty() {
f.frame().print_raw(frame.frame.ip(), None, None, None)?;
} else {
for symbol in frame.symbols.iter() {
f.frame().print_raw_with_column(
frame.frame.ip(),
symbol.name.as_ref().map(|b| backtrace_rs::SymbolName::new(b)),
symbol.filename.as_ref().map(|b| match b {
BytesOrWide::Bytes(w) => BytesOrWideString::Bytes(w),
BytesOrWide::Wide(w) => BytesOrWideString::Wide(w),
}),
symbol.lineno,
symbol.colno,
)?;
}
}
}
f.finish()?;
Ok(())
}
}
type LazyResolve = impl (FnOnce() -> Capture) + Send + Sync + UnwindSafe;
fn lazy_resolve(mut capture: Capture) -> LazyResolve {
move || {
// Use the global backtrace lock to synchronize this as it's a
// requirement of the `backtrace` crate, and then actually resolve
// everything.
let _lock = lock();
for frame in capture.frames.iter_mut() {
let symbols = &mut frame.symbols;
let frame = match &frame.frame {
RawFrame::Actual(frame) => frame,
#[cfg(test)]
RawFrame::Fake => unimplemented!(),
};
unsafe {
backtrace_rs::resolve_frame_unsynchronized(frame, |symbol| {
symbols.push(BacktraceSymbol {
name: symbol.name().map(|m| m.as_bytes().to_vec()),
filename: symbol.filename_raw().map(|b| match b {
BytesOrWideString::Bytes(b) => BytesOrWide::Bytes(b.to_owned()),
BytesOrWideString::Wide(b) => BytesOrWide::Wide(b.to_owned()),
}),
lineno: symbol.lineno(),
colno: symbol.colno(),
});
});
}
}
capture
}
}
impl RawFrame {
fn ip(&self) -> *mut c_void {
match self {
RawFrame::Actual(frame) => frame.ip(),
#[cfg(test)]
RawFrame::Fake => crate::ptr::invalid_mut(1),
}
}
}