backtrace.rs.html -- source
Description: Source to the Rust file `src/libstd/sys_common/backtrace.rs`.
Keywords: rust, rustlang, rust-lang

      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

    use crate::borrow::Cow;
    /// Common code for printing the backtrace in the same way across the different
    /// supported platforms.
    use crate::env;
    use crate::fmt;
    use crate::io;
    use crate::io::prelude::*;
    use crate::path::{self, Path, PathBuf};
    use crate::sync::atomic::{self, Ordering};
    use crate::sys::mutex::Mutex;

    use backtrace_rs::{BacktraceFmt, BytesOrWideString, PrintFmt};

    /// Max number of frames to print.
    const MAX_NB_FRAMES: usize = 100;

    pub fn lock() -> impl Drop {
        struct Guard;
        static LOCK: Mutex = Mutex::new();

        impl Drop for Guard {
            fn drop(&mut self) {
                unsafe {
                    LOCK.unlock();
                }
            }
        }

        unsafe {
            LOCK.lock();
            Guard
        }
    }

    /// Prints the current backtrace.
    pub fn print(w: &mut dyn Write, format: PrintFmt) -> io::Result<()> {
        // There are issues currently linking libbacktrace into tests, and in
        // general during libstd's own unit tests we're not testing this path. In
        // test mode immediately return here to optimize away any references to the
        // libbacktrace symbols
        if cfg!(test) {
            return Ok(());
        }

        // Use a lock to prevent mixed output in multithreading context.
        // Some platforms also requires it, like `SymFromAddr` on Windows.
        unsafe {
            let _lock = lock();
            _print(w, format)
        }
    }

    unsafe fn _print(w: &mut dyn Write, format: PrintFmt) -> io::Result<()> {
        struct DisplayBacktrace {
            format: PrintFmt,
        }
        impl fmt::Display for DisplayBacktrace {
            fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
                unsafe { _print_fmt(fmt, self.format) }
            }
        }
        write!(w, "{}", DisplayBacktrace { format })
    }

    unsafe fn _print_fmt(fmt: &mut fmt::Formatter<'_>, print_fmt: PrintFmt) -> fmt::Result {
        // Always 'fail' to get the cwd when running under Miri -
        // this allows Miri to display backtraces in isolation mode
        let cwd = if !cfg!(miri) { env::current_dir().ok() } else { None };

        let mut print_path = move |fmt: &mut fmt::Formatter<'_>, bows: BytesOrWideString<'_>| {
            output_filename(fmt, bows, print_fmt, cwd.as_ref())
        };
        writeln!(fmt, "stack backtrace:")?;
        let mut bt_fmt = BacktraceFmt::new(fmt, print_fmt, &mut print_path);
        bt_fmt.add_context()?;
        let mut idx = 0;
        let mut res = Ok(());
        backtrace_rs::trace_unsynchronized(|frame| {
            if print_fmt == PrintFmt::Short && idx > MAX_NB_FRAMES {
                return false;
            }

            let mut hit = false;
            let mut stop = false;
            backtrace_rs::resolve_frame_unsynchronized(frame, |symbol| {
                hit = true;
                if print_fmt == PrintFmt::Short {
                    if let Some(sym) = symbol.name().and_then(|s| s.as_str()) {
                        if sym.contains("__rust_begin_short_backtrace") {
                            stop = true;
                            return;
                        }
                    }
                }

                res = bt_fmt.frame().symbol(frame, symbol);
            });
            if stop {
                return false;
            }
            if !hit {
                res = bt_fmt.frame().print_raw(frame.ip(), None, None, None);
            }

            idx += 1;
            res.is_ok()
        });
        res?;
        bt_fmt.finish()?;
        if print_fmt == PrintFmt::Short {
            writeln!(
                fmt,
                "note: Some details are omitted, \
                 run with `RUST_BACKTRACE=full` for a verbose backtrace."
            )?;
        }
        Ok(())
    }

    /// Fixed frame used to clean the backtrace with `RUST_BACKTRACE=1`. Note that
    /// this is only inline(never) when backtraces in libstd are enabled, otherwise
    /// it's fine to optimize away.
    #[cfg_attr(feature = "backtrace", inline(never))]
    pub fn __rust_begin_short_backtrace<F, T>(f: F) -> T
    where
        F: FnOnce() -> T,
        F: Send,
        T: Send,
    {
        f()
    }

    pub enum RustBacktrace {
        Print(PrintFmt),
        Disabled,
        RuntimeDisabled,
    }

    // For now logging is turned off by default, and this function checks to see
    // whether the magical environment variable is present to see if it's turned on.
    pub fn rust_backtrace_env() -> RustBacktrace {
        // If the `backtrace` feature of this crate isn't enabled quickly return
        // `None` so this can be constant propagated all over the place to turn
        // optimize away callers.
        if !cfg!(feature = "backtrace") {
            return RustBacktrace::Disabled;
        }

        // Setting environment variables for Fuchsia components isn't a standard
        // or easily supported workflow. For now, always display backtraces.
        if cfg!(target_os = "fuchsia") {
            return RustBacktrace::Print(PrintFmt::Full);
        }

        static ENABLED: atomic::AtomicIsize = atomic::AtomicIsize::new(0);
        match ENABLED.load(Ordering::SeqCst) {
            0 => {}
            1 => return RustBacktrace::RuntimeDisabled,
            2 => return RustBacktrace::Print(PrintFmt::Short),
            _ => return RustBacktrace::Print(PrintFmt::Full),
        }

        let (format, cache) = env::var_os("RUST_BACKTRACE")
            .map(|x| {
                if &x == "0" {
                    (RustBacktrace::RuntimeDisabled, 1)
                } else if &x == "full" {
                    (RustBacktrace::Print(PrintFmt::Full), 3)
                } else {
                    (RustBacktrace::Print(PrintFmt::Short), 2)
                }
            })
            .unwrap_or((RustBacktrace::RuntimeDisabled, 1));
        ENABLED.store(cache, Ordering::SeqCst);
        format
    }

    /// Prints the filename of the backtrace frame.
    ///
    /// See also `output`.
    pub fn output_filename(
        fmt: &mut fmt::Formatter<'_>,
        bows: BytesOrWideString<'_>,
        print_fmt: PrintFmt,
        cwd: Option<&PathBuf>,
    ) -> fmt::Result {
        let file: Cow<'_, Path> = match bows {
            #[cfg(unix)]
            BytesOrWideString::Bytes(bytes) => {
                use crate::os::unix::prelude::*;
                Path::new(crate::ffi::OsStr::from_bytes(bytes)).into()
            }
            #[cfg(not(unix))]
            BytesOrWideString::Bytes(bytes) => {
                Path::new(crate::str::from_utf8(bytes).unwrap_or("<unknown>")).into()
            }
            #[cfg(windows)]
            BytesOrWideString::Wide(wide) => {
                use crate::os::windows::prelude::*;
                Cow::Owned(crate::ffi::OsString::from_wide(wide).into())
            }
            #[cfg(not(windows))]
            BytesOrWideString::Wide(_wide) => Path::new("<unknown>").into(),
        };
        if print_fmt == PrintFmt::Short && file.is_absolute() {
            if let Some(cwd) = cwd {
                if let Ok(stripped) = file.strip_prefix(&cwd) {
                    if let Some(s) = stripped.to_str() {
                        return write!(fmt, ".{}{}", path::MAIN_SEPARATOR, s);
                    }
                }
            }
        }
        fmt::Display::fmt(&file.display(), fmt)
    }