mv std libs to library/
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875 changed files with 1255 additions and 1223 deletions
493
library/std/src/backtrace.rs
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493
library/std/src/backtrace.rs
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//! Support for capturing a stack backtrace of an OS thread
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//!
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//! This module contains the support necessary to capture a stack backtrace of a
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//! running OS thread from the OS thread itself. The `Backtrace` type supports
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//! capturing a stack trace via the `Backtrace::capture` and
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//! `Backtrace::force_capture` functions.
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//!
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//! A backtrace is typically quite handy to attach to errors (e.g. types
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//! implementing `std::error::Error`) to get a causal chain of where an error
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//! was generated.
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//!
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//! > **Note**: this module is unstable and is designed in [RFC 2504], and you
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//! > can learn more about its status in the [tracking issue].
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//!
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//! [RFC 2504]: https://github.com/rust-lang/rfcs/blob/master/text/2504-fix-error.md
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//! [tracking issue]: https://github.com/rust-lang/rust/issues/53487
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//!
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//! ## Accuracy
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//!
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//! Backtraces are attempted to be as accurate as possible, but no guarantees
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//! are provided about the exact accuracy of a backtrace. Instruction pointers,
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//! symbol names, filenames, line numbers, etc, may all be incorrect when
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//! reported. Accuracy is attempted on a best-effort basis, however, and bugs
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//! are always welcome to indicate areas of improvement!
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//!
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//! For most platforms a backtrace with a filename/line number requires that
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//! programs be compiled with debug information. Without debug information
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//! filenames/line numbers will not be reported.
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//!
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//! ## Platform support
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//!
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//! Not all platforms that libstd compiles for support capturing backtraces.
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//! Some platforms simply do nothing when capturing a backtrace. To check
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//! whether the platform supports capturing backtraces you can consult the
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//! `BacktraceStatus` enum as a result of `Backtrace::status`.
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//!
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//! Like above with accuracy platform support is done on a best effort basis.
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//! Sometimes libraries may not be available at runtime or something may go
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//! wrong which would cause a backtrace to not be captured. Please feel free to
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//! report issues with platforms where a backtrace cannot be captured though!
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//!
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//! ## Environment Variables
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//!
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//! The `Backtrace::capture` function may not actually capture a backtrace by
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//! default. Its behavior is governed by two environment variables:
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//!
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//! * `RUST_LIB_BACKTRACE` - if this is set to `0` then `Backtrace::capture`
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//! will never capture a backtrace. Any other value this is set to will enable
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//! `Backtrace::capture`.
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//!
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//! * `RUST_BACKTRACE` - if `RUST_LIB_BACKTRACE` is not set, then this variable
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//! is consulted with the same rules of `RUST_LIB_BACKTRACE`.
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//!
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//! * If neither of the above env vars are set, then `Backtrace::capture` will
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//! be disabled.
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//!
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//! Capturing a backtrace can be a quite expensive runtime operation, so the
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//! environment variables allow either forcibly disabling this runtime
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//! performance hit or allow selectively enabling it in some programs.
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//!
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//! Note that the `Backtrace::force_capture` function can be used to ignore
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//! these environment variables. Also note that the state of environment
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//! variables is cached once the first backtrace is created, so altering
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//! `RUST_LIB_BACKTRACE` or `RUST_BACKTRACE` at runtime may not actually change
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//! how backtraces are captured.
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#![unstable(feature = "backtrace", issue = "53487")]
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// NB: A note on resolution of a backtrace:
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//
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// Backtraces primarily happen in two steps, one is where we actually capture
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// the stack backtrace, giving us a list of instruction pointers corresponding
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// to stack frames. Next we take these instruction pointers and, one-by-one,
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// turn them into a human readable name (like `main`).
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//
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// The first phase can be somewhat expensive (walking the stack), especially
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// on MSVC where debug information is consulted to return inline frames each as
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// their own frame. The second phase, however, is almost always extremely
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// expensive (on the order of milliseconds sometimes) when it's consulting debug
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// information.
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//
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// We attempt to amortize this cost as much as possible by delaying resolution
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// of an address to a human readable name for as long as possible. When
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// `Backtrace::create` is called to capture a backtrace it doesn't actually
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// perform any symbol resolution, but rather we lazily resolve symbols only just
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// before they're needed for printing. This way we can make capturing a
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// backtrace and throwing it away much cheaper, but actually printing a
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// backtrace is still basically the same cost.
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//
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// This strategy comes at the cost of some synchronization required inside of a
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// `Backtrace`, but that's a relatively small price to pay relative to capturing
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// a backtrace or actually symbolizing it.
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use crate::env;
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use crate::ffi::c_void;
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use crate::fmt;
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use crate::sync::atomic::{AtomicUsize, Ordering::SeqCst};
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use crate::sync::Mutex;
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use crate::sys_common::backtrace::{lock, output_filename};
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use crate::vec::Vec;
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use backtrace::BytesOrWideString;
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use backtrace_rs as backtrace;
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/// A captured OS thread stack backtrace.
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///
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/// This type represents a stack backtrace for an OS thread captured at a
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/// previous point in time. In some instances the `Backtrace` type may
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/// internally be empty due to configuration. For more information see
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/// `Backtrace::capture`.
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pub struct Backtrace {
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inner: Inner,
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}
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/// The current status of a backtrace, indicating whether it was captured or
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/// whether it is empty for some other reason.
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#[non_exhaustive]
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#[derive(Debug, PartialEq, Eq)]
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pub enum BacktraceStatus {
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/// Capturing a backtrace is not supported, likely because it's not
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/// implemented for the current platform.
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Unsupported,
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/// Capturing a backtrace has been disabled through either the
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/// `RUST_LIB_BACKTRACE` or `RUST_BACKTRACE` environment variables.
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Disabled,
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/// A backtrace has been captured and the `Backtrace` should print
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/// reasonable information when rendered.
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Captured,
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}
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enum Inner {
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Unsupported,
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Disabled,
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Captured(Mutex<Capture>),
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}
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struct Capture {
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actual_start: usize,
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resolved: bool,
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frames: Vec<BacktraceFrame>,
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}
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fn _assert_send_sync() {
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fn _assert<T: Send + Sync>() {}
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_assert::<Backtrace>();
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}
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struct BacktraceFrame {
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frame: RawFrame,
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symbols: Vec<BacktraceSymbol>,
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}
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enum RawFrame {
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Actual(backtrace::Frame),
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#[cfg(test)]
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Fake,
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}
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struct BacktraceSymbol {
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name: Option<Vec<u8>>,
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filename: Option<BytesOrWide>,
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lineno: Option<u32>,
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}
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enum BytesOrWide {
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Bytes(Vec<u8>),
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Wide(Vec<u16>),
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}
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impl fmt::Debug for Backtrace {
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fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
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let mut capture = match &self.inner {
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Inner::Unsupported => return fmt.write_str("<unsupported>"),
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Inner::Disabled => return fmt.write_str("<disabled>"),
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Inner::Captured(c) => c.lock().unwrap(),
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};
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capture.resolve();
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let frames = &capture.frames[capture.actual_start..];
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write!(fmt, "Backtrace ")?;
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let mut dbg = fmt.debug_list();
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for frame in frames {
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if frame.frame.ip().is_null() {
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continue;
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}
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dbg.entries(&frame.symbols);
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}
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dbg.finish()
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}
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}
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impl fmt::Debug for BacktraceSymbol {
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fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
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write!(fmt, "{{ ")?;
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if let Some(fn_name) = self.name.as_ref().map(|b| backtrace::SymbolName::new(b)) {
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write!(fmt, "fn: \"{:#}\"", fn_name)?;
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} else {
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write!(fmt, "fn: <unknown>")?;
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}
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if let Some(fname) = self.filename.as_ref() {
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write!(fmt, ", file: \"{:?}\"", fname)?;
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}
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if let Some(line) = self.lineno.as_ref() {
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write!(fmt, ", line: {:?}", line)?;
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}
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write!(fmt, " }}")
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}
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}
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impl fmt::Debug for BytesOrWide {
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fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
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output_filename(
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fmt,
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match self {
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BytesOrWide::Bytes(w) => BytesOrWideString::Bytes(w),
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BytesOrWide::Wide(w) => BytesOrWideString::Wide(w),
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},
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backtrace::PrintFmt::Short,
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crate::env::current_dir().as_ref().ok(),
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)
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}
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}
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impl Backtrace {
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/// Returns whether backtrace captures are enabled through environment
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/// variables.
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fn enabled() -> bool {
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// Cache the result of reading the environment variables to make
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// backtrace captures speedy, because otherwise reading environment
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// variables every time can be somewhat slow.
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static ENABLED: AtomicUsize = AtomicUsize::new(0);
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match ENABLED.load(SeqCst) {
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0 => {}
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1 => return false,
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_ => return true,
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}
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let enabled = match env::var("RUST_LIB_BACKTRACE") {
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Ok(s) => s != "0",
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Err(_) => match env::var("RUST_BACKTRACE") {
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Ok(s) => s != "0",
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Err(_) => false,
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},
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};
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ENABLED.store(enabled as usize + 1, SeqCst);
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enabled
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}
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/// Capture a stack backtrace of the current thread.
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///
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/// This function will capture a stack backtrace of the current OS thread of
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/// execution, returning a `Backtrace` type which can be later used to print
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/// the entire stack trace or render it to a string.
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///
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/// This function will be a noop if the `RUST_BACKTRACE` or
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/// `RUST_LIB_BACKTRACE` backtrace variables are both not set. If either
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/// environment variable is set and enabled then this function will actually
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/// capture a backtrace. Capturing a backtrace can be both memory intensive
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/// and slow, so these environment variables allow liberally using
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/// `Backtrace::capture` and only incurring a slowdown when the environment
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/// variables are set.
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///
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/// To forcibly capture a backtrace regardless of environment variables, use
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/// the `Backtrace::force_capture` function.
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#[inline(never)] // want to make sure there's a frame here to remove
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pub fn capture() -> Backtrace {
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if !Backtrace::enabled() {
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return Backtrace { inner: Inner::Disabled };
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}
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Backtrace::create(Backtrace::capture as usize)
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}
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/// Forcibly captures a full backtrace, regardless of environment variable
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/// configuration.
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///
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/// This function behaves the same as `capture` except that it ignores the
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/// values of the `RUST_BACKTRACE` and `RUST_LIB_BACKTRACE` environment
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/// variables, always capturing a backtrace.
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///
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/// Note that capturing a backtrace can be an expensive operation on some
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/// platforms, so this should be used with caution in performance-sensitive
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/// parts of code.
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#[inline(never)] // want to make sure there's a frame here to remove
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pub fn force_capture() -> Backtrace {
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Backtrace::create(Backtrace::force_capture as usize)
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}
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/// Forcibly captures a disabled backtrace, regardless of environment
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/// variable configuration.
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pub const fn disabled() -> Backtrace {
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Backtrace { inner: Inner::Disabled }
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}
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// Capture a backtrace which start just before the function addressed by
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// `ip`
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fn create(ip: usize) -> Backtrace {
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let _lock = lock();
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let mut frames = Vec::new();
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let mut actual_start = None;
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unsafe {
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backtrace::trace_unsynchronized(|frame| {
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frames.push(BacktraceFrame {
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frame: RawFrame::Actual(frame.clone()),
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symbols: Vec::new(),
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});
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if frame.symbol_address() as usize == ip && actual_start.is_none() {
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actual_start = Some(frames.len());
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}
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true
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});
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}
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// If no frames came out assume that this is an unsupported platform
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// since `backtrace` doesn't provide a way of learning this right now,
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// and this should be a good enough approximation.
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let inner = if frames.is_empty() {
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Inner::Unsupported
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} else {
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Inner::Captured(Mutex::new(Capture {
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actual_start: actual_start.unwrap_or(0),
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frames,
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resolved: false,
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}))
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};
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Backtrace { inner }
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}
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/// Returns the status of this backtrace, indicating whether this backtrace
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/// request was unsupported, disabled, or a stack trace was actually
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/// captured.
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pub fn status(&self) -> BacktraceStatus {
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match self.inner {
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Inner::Unsupported => BacktraceStatus::Unsupported,
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Inner::Disabled => BacktraceStatus::Disabled,
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Inner::Captured(_) => BacktraceStatus::Captured,
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}
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}
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}
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impl fmt::Display for Backtrace {
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fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
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let mut capture = match &self.inner {
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Inner::Unsupported => return fmt.write_str("unsupported backtrace"),
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Inner::Disabled => return fmt.write_str("disabled backtrace"),
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Inner::Captured(c) => c.lock().unwrap(),
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};
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capture.resolve();
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let full = fmt.alternate();
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let (frames, style) = if full {
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(&capture.frames[..], backtrace::PrintFmt::Full)
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} else {
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(&capture.frames[capture.actual_start..], backtrace::PrintFmt::Short)
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};
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// When printing paths we try to strip the cwd if it exists, otherwise
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// we just print the path as-is. Note that we also only do this for the
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// short format, because if it's full we presumably want to print
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// everything.
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let cwd = crate::env::current_dir();
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let mut print_path = move |fmt: &mut fmt::Formatter<'_>, path: BytesOrWideString<'_>| {
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output_filename(fmt, path, style, cwd.as_ref().ok())
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};
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let mut f = backtrace::BacktraceFmt::new(fmt, style, &mut print_path);
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f.add_context()?;
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for frame in frames {
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let mut f = f.frame();
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if frame.symbols.is_empty() {
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f.print_raw(frame.frame.ip(), None, None, None)?;
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} else {
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for symbol in frame.symbols.iter() {
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f.print_raw(
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frame.frame.ip(),
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symbol.name.as_ref().map(|b| backtrace::SymbolName::new(b)),
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symbol.filename.as_ref().map(|b| match b {
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BytesOrWide::Bytes(w) => BytesOrWideString::Bytes(w),
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BytesOrWide::Wide(w) => BytesOrWideString::Wide(w),
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}),
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symbol.lineno,
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)?;
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}
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}
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}
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f.finish()?;
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Ok(())
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}
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}
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impl Capture {
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fn resolve(&mut self) {
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// If we're already resolved, nothing to do!
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if self.resolved {
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return;
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}
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self.resolved = true;
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// Use the global backtrace lock to synchronize this as it's a
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// requirement of the `backtrace` crate, and then actually resolve
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// everything.
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let _lock = lock();
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for frame in self.frames.iter_mut() {
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let symbols = &mut frame.symbols;
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let frame = match &frame.frame {
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RawFrame::Actual(frame) => frame,
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#[cfg(test)]
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RawFrame::Fake => unimplemented!(),
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};
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unsafe {
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backtrace::resolve_frame_unsynchronized(frame, |symbol| {
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symbols.push(BacktraceSymbol {
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name: symbol.name().map(|m| m.as_bytes().to_vec()),
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filename: symbol.filename_raw().map(|b| match b {
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BytesOrWideString::Bytes(b) => BytesOrWide::Bytes(b.to_owned()),
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BytesOrWideString::Wide(b) => BytesOrWide::Wide(b.to_owned()),
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}),
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lineno: symbol.lineno(),
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});
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});
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}
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}
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}
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}
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impl RawFrame {
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fn ip(&self) -> *mut c_void {
|
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match self {
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RawFrame::Actual(frame) => frame.ip(),
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#[cfg(test)]
|
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RawFrame::Fake => 1 as *mut c_void,
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}
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}
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}
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#[test]
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fn test_debug() {
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let backtrace = Backtrace {
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inner: Inner::Captured(Mutex::new(Capture {
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actual_start: 1,
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resolved: true,
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frames: vec![
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BacktraceFrame {
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frame: RawFrame::Fake,
|
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symbols: vec![BacktraceSymbol {
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name: Some(b"std::backtrace::Backtrace::create".to_vec()),
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filename: Some(BytesOrWide::Bytes(b"rust/backtrace.rs".to_vec())),
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lineno: Some(100),
|
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}],
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},
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BacktraceFrame {
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frame: RawFrame::Fake,
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symbols: vec![BacktraceSymbol {
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name: Some(b"__rust_maybe_catch_panic".to_vec()),
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filename: None,
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lineno: None,
|
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}],
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},
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BacktraceFrame {
|
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frame: RawFrame::Fake,
|
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symbols: vec![
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BacktraceSymbol {
|
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name: Some(b"std::rt::lang_start_internal".to_vec()),
|
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filename: Some(BytesOrWide::Bytes(b"rust/rt.rs".to_vec())),
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lineno: Some(300),
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},
|
||||
BacktraceSymbol {
|
||||
name: Some(b"std::rt::lang_start".to_vec()),
|
||||
filename: Some(BytesOrWide::Bytes(b"rust/rt.rs".to_vec())),
|
||||
lineno: Some(400),
|
||||
},
|
||||
],
|
||||
},
|
||||
],
|
||||
})),
|
||||
};
|
||||
|
||||
#[rustfmt::skip]
|
||||
let expected = "Backtrace [\
|
||||
\n { fn: \"__rust_maybe_catch_panic\" },\
|
||||
\n { fn: \"std::rt::lang_start_internal\", file: \"rust/rt.rs\", line: 300 },\
|
||||
\n { fn: \"std::rt::lang_start\", file: \"rust/rt.rs\", line: 400 },\
|
||||
\n]";
|
||||
|
||||
assert_eq!(format!("{:#?}", backtrace), expected);
|
||||
}
|
||||
Loading…
Add table
Add a link
Reference in a new issue