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

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    // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    /// Common code for printing the backtrace in the same way across the different
    /// supported platforms.

    use env;
    use io::prelude::*;
    use io;
    use str;
    use sync::atomic::{self, Ordering};
    use path::{self, Path};
    use sys::mutex::Mutex;
    use ptr;

    pub use sys::backtrace::{
        unwind_backtrace,
        resolve_symname,
        foreach_symbol_fileline,
        BacktraceContext
    };

    #[cfg(target_pointer_width = "64")]
    pub const HEX_WIDTH: usize = 18;

    #[cfg(target_pointer_width = "32")]
    pub const HEX_WIDTH: usize = 10;

    /// Represents an item in the backtrace list. See `unwind_backtrace` for how
    /// it is created.
    #[derive(Debug, Copy, Clone)]
    pub struct Frame {
        /// Exact address of the call that failed.
        pub exact_position: *const u8,
        /// Address of the enclosing function.
        pub symbol_addr: *const u8,
        /// Which inlined function is this frame referring to
        pub inline_context: u32,
    }

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

    /// Prints the current backtrace.
    pub fn print(w: &mut dyn Write, format: PrintFormat) -> io::Result<()> {
        static LOCK: Mutex = Mutex::new();

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

    fn _print(w: &mut dyn Write, format: PrintFormat) -> io::Result<()> {
        let mut frames = [Frame {
            exact_position: ptr::null(),
            symbol_addr: ptr::null(),
            inline_context: 0,
        }; MAX_NB_FRAMES];
        let (nb_frames, context) = unwind_backtrace(&mut frames)?;
        let (skipped_before, skipped_after) =
            filter_frames(&frames[..nb_frames], format, &context);
        if skipped_before + skipped_after > 0 {
            writeln!(w, "note: Some details are omitted, \
                         run with `RUST_BACKTRACE=full` for a verbose backtrace.")?;
        }
        writeln!(w, "stack backtrace:")?;

        let filtered_frames = &frames[..nb_frames - skipped_after];
        for (index, frame) in filtered_frames.iter().skip(skipped_before).enumerate() {
            resolve_symname(*frame, |symname| {
                output(w, index, *frame, symname, format)
            }, &context)?;
            let has_more_filenames = foreach_symbol_fileline(*frame, |file, line| {
                output_fileline(w, file, line, format)
            }, &context)?;
            if has_more_filenames {
                w.write_all(b" <... and possibly more>")?;
            }
        }

        Ok(())
    }

    /// Returns a number of frames to remove at the beginning and at the end of the
    /// backtrace, according to the backtrace format.
    fn filter_frames(frames: &[Frame],
                     format: PrintFormat,
                     context: &BacktraceContext) -> (usize, usize)
    {
        if format == PrintFormat::Full {
            return (0, 0);
        }

        let skipped_before = 0;

        let skipped_after = frames.len() - frames.iter().position(|frame| {
            let mut is_marker = false;
            let _ = resolve_symname(*frame, |symname| {
                if let Some(mangled_symbol_name) = symname {
                    // Use grep to find the concerned functions
                    if mangled_symbol_name.contains("__rust_begin_short_backtrace") {
                        is_marker = true;
                    }
                }
                Ok(())
            }, context);
            is_marker
        }).unwrap_or(frames.len());

        if skipped_before + skipped_after >= frames.len() {
            // Avoid showing completely empty backtraces
            return (0, 0);
        }

        (skipped_before, skipped_after)
    }

    /// Fixed frame used to clean the backtrace with `RUST_BACKTRACE=1`.
    #[inline(never)]
    pub fn __rust_begin_short_backtrace<F, T>(f: F) -> T
        where F: FnOnce() -> T, F: Send, T: Send
    {
        f()
    }

    /// Controls how the backtrace should be formatted.
    #[derive(Debug, Copy, Clone, Eq, PartialEq)]
    pub enum PrintFormat {
        /// Show only relevant data from the backtrace.
        Short = 2,
        /// Show all the frames with absolute path for files.
        Full = 3,
    }

    // 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 log_enabled() -> Option<PrintFormat> {
        static ENABLED: atomic::AtomicIsize = atomic::AtomicIsize::new(0);
        match ENABLED.load(Ordering::SeqCst) {
            0 => {}
            1 => return None,
            2 => return Some(PrintFormat::Short),
            _ => return Some(PrintFormat::Full),
        }

        let val = env::var_os("RUST_BACKTRACE").and_then(|x|
            if &x == "0" {
                None
            } else if &x == "full" {
                Some(PrintFormat::Full)
            } else {
                Some(PrintFormat::Short)
            }
        );
        ENABLED.store(match val {
            Some(v) => v as isize,
            None => 1,
        }, Ordering::SeqCst);
        val
    }

    /// Print the symbol of the backtrace frame.
    ///
    /// These output functions should now be used everywhere to ensure consistency.
    /// You may want to also use `output_fileline`.
    fn output(w: &mut dyn Write, idx: usize, frame: Frame,
                  s: Option<&str>, format: PrintFormat) -> io::Result<()> {
        // Remove the `17: 0x0 - <unknown>` line.
        if format == PrintFormat::Short && frame.exact_position == ptr::null() {
            return Ok(());
        }
        match format {
            PrintFormat::Full => write!(w,
                                        "  {:2}: {:2$?} - ",
                                        idx,
                                        frame.exact_position,
                                        HEX_WIDTH)?,
            PrintFormat::Short => write!(w, "  {:2}: ", idx)?,
        }
        match s {
            Some(string) => demangle(w, string, format)?,
            None => w.write_all(b"<unknown>")?,
        }
        w.write_all(b"\n")
    }

    /// Print the filename and line number of the backtrace frame.
    ///
    /// See also `output`.
    #[allow(dead_code)]
    fn output_fileline(w: &mut dyn Write,
                       file: &[u8],
                       line: u32,
                       format: PrintFormat) -> io::Result<()> {
        // prior line: "  ##: {:2$} - func"
        w.write_all(b"")?;
        match format {
            PrintFormat::Full => write!(w,
                                        "           {:1$}",
                                        "",
                                        HEX_WIDTH)?,
            PrintFormat::Short => write!(w, "           ")?,
        }

        let file = str::from_utf8(file).unwrap_or("<unknown>");
        let file_path = Path::new(file);
        let mut already_printed = false;
        if format == PrintFormat::Short && file_path.is_absolute() {
            if let Ok(cwd) = env::current_dir() {
                if let Ok(stripped) = file_path.strip_prefix(&cwd) {
                    if let Some(s) = stripped.to_str() {
                        write!(w, "  at .{}{}:{}", path::MAIN_SEPARATOR, s, line)?;
                        already_printed = true;
                    }
                }
            }
        }
        if !already_printed {
            write!(w, "  at {}:{}", file, line)?;
        }

        w.write_all(b"\n")
    }

    // All rust symbols are in theory lists of "::"-separated identifiers. Some
    // assemblers, however, can't handle these characters in symbol names. To get
    // around this, we use C++-style mangling. The mangling method is:
    //
    // 1. Prefix the symbol with "_ZN"
    // 2. For each element of the path, emit the length plus the element
    // 3. End the path with "E"
    //
    // For example, "_ZN4testE" => "test" and "_ZN3foo3barE" => "foo::bar".
    //
    // We're the ones printing our backtraces, so we can't rely on anything else to
    // demangle our symbols. It's *much* nicer to look at demangled symbols, so
    // this function is implemented to give us nice pretty output.
    //
    // Note that this demangler isn't quite as fancy as it could be. We have lots
    // of other information in our symbols like hashes, version, type information,
    // etc. Additionally, this doesn't handle glue symbols at all.
    pub fn demangle(writer: &mut dyn Write, mut s: &str, format: PrintFormat) -> io::Result<()> {
        // During ThinLTO LLVM may import and rename internal symbols, so strip out
        // those endings first as they're one of the last manglings applied to
        // symbol names.
        let llvm = ".llvm.";
        if let Some(i) = s.find(llvm) {
            let candidate = &s[i + llvm.len()..];
            let all_hex = candidate.chars().all(|c| {
                match c {
                    'A' ..= 'F' | '0' ..= '9' => true,
                    _ => false,
                }
            });

            if all_hex {
                s = &s[..i];
            }
        }

        // Validate the symbol. If it doesn't look like anything we're
        // expecting, we just print it literally. Note that we must handle non-rust
        // symbols because we could have any function in the backtrace.
        let mut valid = true;
        let mut inner = s;
        if s.len() > 4 && s.starts_with("_ZN") && s.ends_with("E") {
            inner = &s[3 .. s.len() - 1];
        // On Windows, dbghelp strips leading underscores, so we accept "ZN...E" form too.
        } else if s.len() > 3 && s.starts_with("ZN") && s.ends_with("E") {
            inner = &s[2 .. s.len() - 1];
        } else {
            valid = false;
        }

        if valid {
            let mut chars = inner.chars();
            while valid {
                let mut i = 0;
                for c in chars.by_ref() {
                    if c.is_numeric() {
                        i = i * 10 + c as usize - '0' as usize;
                    } else {
                        break
                    }
                }
                if i == 0 {
                    valid = chars.next().is_none();
                    break
                } else if chars.by_ref().take(i - 1).count() != i - 1 {
                    valid = false;
                }
            }
        }

        // Alright, let's do this.
        if !valid {
            writer.write_all(s.as_bytes())?;
        } else {
            // remove the `::hfc2edb670e5eda97` part at the end of the symbol.
            if format == PrintFormat::Short {
                // The symbol in still mangled.
                let mut split = inner.rsplitn(2, "17h");
                match (split.next(), split.next()) {
                    (Some(addr), rest) => {
                        if addr.len() == 16 &&
                           addr.chars().all(|c| c.is_digit(16))
                        {
                            inner = rest.unwrap_or("");
                        }
                    }
                    _ => (),
                }
            }

            let mut first = true;
            while !inner.is_empty() {
                if !first {
                    writer.write_all(b"::")?;
                } else {
                    first = false;
                }
                let mut rest = inner;
                while rest.chars().next().unwrap().is_numeric() {
                    rest = &rest[1..];
                }
                let i: usize = inner[.. (inner.len() - rest.len())].parse().unwrap();
                inner = &rest[i..];
                rest = &rest[..i];
                if rest.starts_with("_$") {
                    rest = &rest[1..];
                }
                while !rest.is_empty() {
                    if rest.starts_with(".") {
                        if let Some('.') = rest[1..].chars().next() {
                            writer.write_all(b"::")?;
                            rest = &rest[2..];
                        } else {
                            writer.write_all(b".")?;
                            rest = &rest[1..];
                        }
                    } else if rest.starts_with("$") {
                        macro_rules! demangle {
                            ($($pat:expr => $demangled:expr),*) => ({
                                $(if rest.starts_with($pat) {
                                    writer.write_all($demangled)?;
                                    rest = &rest[$pat.len()..];
                                  } else)*
                                {
                                    writer.write_all(rest.as_bytes())?;
                                    break;
                                }

                            })
                        }

                        // see src/librustc/back/link.rs for these mappings
                        demangle! (
                            "$SP$" => b"@",
                            "$BP$" => b"*",
                            "$RF$" => b"&",
                            "$LT$" => b"<",
                            "$GT$" => b">",
                            "$LP$" => b"(",
                            "$RP$" => b")",
                            "$C$" => b",",

                            // in theory we can demangle any Unicode code point, but
                            // for simplicity we just catch the common ones.
                            "$u7e$" => b"~",
                            "$u20$" => b" ",
                            "$u27$" => b"'",
                            "$u5b$" => b"[",
                            "$u5d$" => b"]",
                            "$u7b$" => b"{",
                            "$u7d$" => b"}",
                            "$u3b$" => b";",
                            "$u2b$" => b"+",
                            "$u22$" => b"\""
                        )
                    } else {
                        let idx = match rest.char_indices().find(|&(_, c)| c == '$' || c == '.') {
                            None => rest.len(),
                            Some((i, _)) => i,
                        };
                        writer.write_all(rest[..idx].as_bytes())?;
                        rest = &rest[idx..];
                    }
                }
            }
        }

        Ok(())
    }

    #[cfg(test)]
    mod tests {
        use sys_common;
        macro_rules! t { ($a:expr, $b:expr) => ({
            let mut m = Vec::new();
            sys_common::backtrace::demangle(&mut m,
                                            $a,
                                            super::PrintFormat::Full).unwrap();
            assert_eq!(String::from_utf8(m).unwrap(), $b);
        }) }

        #[test]
        fn demangle() {
            t!("test", "test");
            t!("_ZN4testE", "test");
            t!("_ZN4test", "_ZN4test");
            t!("_ZN4test1a2bcE", "test::a::bc");
        }

        #[test]
        fn demangle_dollars() {
            t!("_ZN4$RP$E", ")");
            t!("_ZN8$RF$testE", "&test");
            t!("_ZN8$BP$test4foobE", "*test::foob");
            t!("_ZN9$u20$test4foobE", " test::foob");
            t!("_ZN35Bar$LT$$u5b$u32$u3b$$u20$4$u5d$$GT$E", "Bar<[u32; 4]>");
        }

        #[test]
        fn demangle_many_dollars() {
            t!("_ZN13test$u20$test4foobE", "test test::foob");
            t!("_ZN12test$BP$test4foobE", "test*test::foob");
        }

        #[test]
        fn demangle_windows() {
            t!("ZN4testE", "test");
            t!("ZN13test$u20$test4foobE", "test test::foob");
            t!("ZN12test$RF$test4foobE", "test&test::foob");
        }

        #[test]
        fn demangle_elements_beginning_with_underscore() {
            t!("_ZN13_$LT$test$GT$E", "<test>");
            t!("_ZN28_$u7b$$u7b$closure$u7d$$u7d$E", "{{closure}}");
            t!("_ZN15__STATIC_FMTSTRE", "__STATIC_FMTSTR");
        }

        #[test]
        fn demangle_trait_impls() {
            t!("_ZN71_$LT$Test$u20$$u2b$$u20$$u27$static$u20$as$u20$foo..Bar$LT$Test$GT$$GT$3barE",
               "<Test + 'static as foo::Bar<Test>>::bar");
        }
    }

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