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    use core::{fmt, str};

    cfg_if::cfg_if! {
        if #[cfg(feature = "std")] {
            use std::path::Path;
            use std::prelude::v1::*;
        }
    }

    use super::backtrace::Frame;
    use super::types::BytesOrWideString;
    use core::ffi::c_void;
    use rustc_demangle::{try_demangle, Demangle};

    /// Resolve an address to a symbol, passing the symbol to the specified
    /// closure.
    ///
    /// This function will look up the given address in areas such as the local
    /// symbol table, dynamic symbol table, or DWARF debug info (depending on the
    /// activated implementation) to find symbols to yield.
    ///
    /// The closure may not be called if resolution could not be performed, and it
    /// also may be called more than once in the case of inlined functions.
    ///
    /// Symbols yielded represent the execution at the specified `addr`, returning
    /// file/line pairs for that address (if available).
    ///
    /// Note that if you have a `Frame` then it's recommended to use the
    /// `resolve_frame` function instead of this one.
    ///
    /// # Required features
    ///
    /// This function requires the `std` feature of the `backtrace` crate to be
    /// enabled, and the `std` feature is enabled by default.
    ///
    /// # Panics
    ///
    /// This function strives to never panic, but if the `cb` provided panics then
    /// some platforms will force a double panic to abort the process. Some
    /// platforms use a C library which internally uses callbacks which cannot be
    /// unwound through, so panicking from `cb` may trigger a process abort.
    ///
    /// # Example
    ///
    /// ```
    /// extern crate backtrace;
    ///
    /// fn main() {
    ///     backtrace::trace(|frame| {
    ///         let ip = frame.ip();
    ///
    ///         backtrace::resolve(ip, |symbol| {
    ///             // ...
    ///         });
    ///
    ///         false // only look at the top frame
    ///     });
    /// }
    /// ```
    #[cfg(feature = "std")]
    pub fn resolve<F: FnMut(&Symbol)>(addr: *mut c_void, cb: F) {
        let _guard = crate::lock::lock();
        unsafe { resolve_unsynchronized(addr, cb) }
    }

    /// Resolve a previously capture frame to a symbol, passing the symbol to the
    /// specified closure.
    ///
    /// This functin performs the same function as `resolve` except that it takes a
    /// `Frame` as an argument instead of an address. This can allow some platform
    /// implementations of backtracing to provide more accurate symbol information
    /// or information about inline frames for example. It's recommended to use this
    /// if you can.
    ///
    /// # Required features
    ///
    /// This function requires the `std` feature of the `backtrace` crate to be
    /// enabled, and the `std` feature is enabled by default.
    ///
    /// # Panics
    ///
    /// This function strives to never panic, but if the `cb` provided panics then
    /// some platforms will force a double panic to abort the process. Some
    /// platforms use a C library which internally uses callbacks which cannot be
    /// unwound through, so panicking from `cb` may trigger a process abort.
    ///
    /// # Example
    ///
    /// ```
    /// extern crate backtrace;
    ///
    /// fn main() {
    ///     backtrace::trace(|frame| {
    ///         backtrace::resolve_frame(frame, |symbol| {
    ///             // ...
    ///         });
    ///
    ///         false // only look at the top frame
    ///     });
    /// }
    /// ```
    #[cfg(feature = "std")]
    pub fn resolve_frame<F: FnMut(&Symbol)>(frame: &Frame, cb: F) {
        let _guard = crate::lock::lock();
        unsafe { resolve_frame_unsynchronized(frame, cb) }
    }

    pub enum ResolveWhat<'a> {
        Address(*mut c_void),
        Frame(&'a Frame),
    }

    impl<'a> ResolveWhat<'a> {
        #[allow(dead_code)]
        fn address_or_ip(&self) -> *mut c_void {
            match self {
                ResolveWhat::Address(a) => adjust_ip(*a),
                ResolveWhat::Frame(f) => adjust_ip(f.ip()),
            }
        }
    }

    // IP values from stack frames are typically (always?) the instruction
    // *after* the call that's the actual stack trace. Symbolizing this on
    // causes the filename/line number to be one ahead and perhaps into
    // the void if it's near the end of the function.
    //
    // This appears to basically always be the case on all platforms, so we always
    // subtract one from a resolved ip to resolve it to the previous call
    // instruction instead of the instruction being returned to.
    //
    // Ideally we would not do this. Ideally we would require callers of the
    // `resolve` APIs here to manually do the -1 and account that they want location
    // information for the *previous* instruction, not the current. Ideally we'd
    // also expose on `Frame` if we are indeed the address of the next instruction
    // or the current.
    //
    // For now though this is a pretty niche concern so we just internally always
    // subtract one. Consumers should keep working and getting pretty good results,
    // so we should be good enough.
    fn adjust_ip(a: *mut c_void) -> *mut c_void {
        if a.is_null() {
            a
        } else {
            (a as usize - 1) as *mut c_void
        }
    }

    /// Same as `resolve`, only unsafe as it's unsynchronized.
    ///
    /// This function does not have synchronization guarentees but is available when
    /// the `std` feature of this crate isn't compiled in. See the `resolve`
    /// function for more documentation and examples.
    ///
    /// # Panics
    ///
    /// See information on `resolve` for caveats on `cb` panicking.
    pub unsafe fn resolve_unsynchronized<F>(addr: *mut c_void, mut cb: F)
    where
        F: FnMut(&Symbol),
    {
        resolve_imp(ResolveWhat::Address(addr), &mut cb)
    }

    /// Same as `resolve_frame`, only unsafe as it's unsynchronized.
    ///
    /// This function does not have synchronization guarentees but is available
    /// when the `std` feature of this crate isn't compiled in. See the
    /// `resolve_frame` function for more documentation and examples.
    ///
    /// # Panics
    ///
    /// See information on `resolve_frame` for caveats on `cb` panicking.
    pub unsafe fn resolve_frame_unsynchronized<F>(frame: &Frame, mut cb: F)
    where
        F: FnMut(&Symbol),
    {
        resolve_imp(ResolveWhat::Frame(frame), &mut cb)
    }

    /// A trait representing the resolution of a symbol in a file.
    ///
    /// This trait is yielded as a trait object to the closure given to the
    /// `backtrace::resolve` function, and it is virtually dispatched as it's
    /// unknown which implementation is behind it.
    ///
    /// A symbol can give contextual information about a function, for example the
    /// name, filename, line number, precise address, etc. Not all information is
    /// always available in a symbol, however, so all methods return an `Option`.
    pub struct Symbol {
        // TODO: this lifetime bound needs to be persisted eventually to `Symbol`,
        // but that's currently a breaking change. For now this is safe since
        // `Symbol` is only ever handed out by reference and can't be cloned.
        inner: SymbolImp<'static>,
    }

    impl Symbol {
        /// Returns the name of this function.
        ///
        /// The returned structure can be used to query various properties about the
        /// symbol name:
        ///
        /// * The `Display` implementation will print out the demangled symbol.
        /// * The raw `str` value of the symbol can be accessed (if it's valid
        ///   utf-8).
        /// * The raw bytes for the symbol name can be accessed.
        pub fn name(&self) -> Option<SymbolName<'_>> {
            self.inner.name()
        }

        /// Returns the starting address of this function.
        pub fn addr(&self) -> Option<*mut c_void> {
            self.inner.addr().map(|p| p as *mut _)
        }

        /// Returns the raw filename as a slice. This is mainly useful for `no_std`
        /// environments.
        pub fn filename_raw(&self) -> Option<BytesOrWideString<'_>> {
            self.inner.filename_raw()
        }

        /// Returns the line number for where this symbol is currently executing.
        ///
        /// This return value is typically `Some` if `filename` returns `Some`, and
        /// is consequently subject to similar caveats.
        pub fn lineno(&self) -> Option<u32> {
            self.inner.lineno()
        }

        /// Returns the file name where this function was defined.
        ///
        /// This is currently only available when libbacktrace is being used (e.g.
        /// unix platforms other than OSX) and when a binary is compiled with
        /// debuginfo. If neither of these conditions is met then this will likely
        /// return `None`.
        ///
        /// # Required features
        ///
        /// This function requires the `std` feature of the `backtrace` crate to be
        /// enabled, and the `std` feature is enabled by default.
        #[cfg(feature = "std")]
        #[allow(unreachable_code)]
        pub fn filename(&self) -> Option<&Path> {
            self.inner.filename()
        }
    }

    impl fmt::Debug for Symbol {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            let mut d = f.debug_struct("Symbol");
            if let Some(name) = self.name() {
                d.field("name", &name);
            }
            if let Some(addr) = self.addr() {
                d.field("addr", &addr);
            }

            #[cfg(feature = "std")]
            {
                if let Some(filename) = self.filename() {
                    d.field("filename", &filename);
                }
            }

            if let Some(lineno) = self.lineno() {
                d.field("lineno", &lineno);
            }
            d.finish()
        }
    }

    cfg_if::cfg_if! {
        if #[cfg(feature = "cpp_demangle")] {
            // Maybe a parsed C++ symbol, if parsing the mangled symbol as Rust
            // failed.
            struct OptionCppSymbol<'a>(Option<::cpp_demangle::BorrowedSymbol<'a>>);

            impl<'a> OptionCppSymbol<'a> {
                fn parse(input: &'a [u8]) -> OptionCppSymbol<'a> {
                    OptionCppSymbol(::cpp_demangle::BorrowedSymbol::new(input).ok())
                }

                fn none() -> OptionCppSymbol<'a> {
                    OptionCppSymbol(None)
                }
            }
        } else {
            use core::marker::PhantomData;

            // Make sure to keep this zero-sized, so that the `cpp_demangle` feature
            // has no cost when disabled.
            struct OptionCppSymbol<'a>(PhantomData<&'a ()>);

            impl<'a> OptionCppSymbol<'a> {
                fn parse(_: &'a [u8]) -> OptionCppSymbol<'a> {
                    OptionCppSymbol(PhantomData)
                }

                fn none() -> OptionCppSymbol<'a> {
                    OptionCppSymbol(PhantomData)
                }
            }
        }
    }

    /// A wrapper around a symbol name to provide ergonomic accessors to the
    /// demangled name, the raw bytes, the raw string, etc.
    // Allow dead code for when the `cpp_demangle` feature is not enabled.
    #[allow(dead_code)]
    pub struct SymbolName<'a> {
        bytes: &'a [u8],
        demangled: Option<Demangle<'a>>,
        cpp_demangled: OptionCppSymbol<'a>,
    }

    impl<'a> SymbolName<'a> {
        /// Creates a new symbol name from the raw underlying bytes.
        pub fn new(bytes: &'a [u8]) -> SymbolName<'a> {
            let str_bytes = str::from_utf8(bytes).ok();
            let demangled = str_bytes.and_then(|s| try_demangle(s).ok());

            let cpp = if demangled.is_none() {
                OptionCppSymbol::parse(bytes)
            } else {
                OptionCppSymbol::none()
            };

            SymbolName {
                bytes: bytes,
                demangled: demangled,
                cpp_demangled: cpp,
            }
        }

        /// Returns the raw (mangled) symbol name as a `str` if the symbol is valid utf-8.
        ///
        /// Use the `Display` implementation if you want the demangled version.
        pub fn as_str(&self) -> Option<&'a str> {
            self.demangled
                .as_ref()
                .map(|s| s.as_str())
                .or_else(|| str::from_utf8(self.bytes).ok())
        }

        /// Returns the raw symbol name as a list of bytes
        pub fn as_bytes(&self) -> &'a [u8] {
            self.bytes
        }
    }

    fn format_symbol_name(
        fmt: fn(&str, &mut fmt::Formatter<'_>) -> fmt::Result,
        mut bytes: &[u8],
        f: &mut fmt::Formatter<'_>,
    ) -> fmt::Result {
        while bytes.len() > 0 {
            match str::from_utf8(bytes) {
                Ok(name) => {
                    fmt(name, f)?;
                    break;
                }
                Err(err) => {
                    fmt("\u{FFFD}", f)?;

                    match err.error_len() {
                        Some(len) => bytes = &bytes[err.valid_up_to() + len..],
                        None => break,
                    }
                }
            }
        }
        Ok(())
    }

    cfg_if::cfg_if! {
        if #[cfg(feature = "cpp_demangle")] {
            impl<'a> fmt::Display for SymbolName<'a> {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    if let Some(ref s) = self.demangled {
                        s.fmt(f)
                    } else if let Some(ref cpp) = self.cpp_demangled.0 {
                        cpp.fmt(f)
                    } else {
                        format_symbol_name(fmt::Display::fmt, self.bytes, f)
                    }
                }
            }
        } else {
            impl<'a> fmt::Display for SymbolName<'a> {
                fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                    if let Some(ref s) = self.demangled {
                        s.fmt(f)
                    } else {
                        format_symbol_name(fmt::Display::fmt, self.bytes, f)
                    }
                }
            }
        }
    }

    cfg_if::cfg_if! {
        if #[cfg(all(feature = "std", feature = "cpp_demangle"))] {
            impl<'a> fmt::Debug for SymbolName<'a> {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    use std::fmt::Write;

                    if let Some(ref s) = self.demangled {
                        return s.fmt(f)
                    }

                    // This may to print if the demangled symbol isn't actually
                    // valid, so handle the error here gracefully by not propagating
                    // it outwards.
                    if let Some(ref cpp) = self.cpp_demangled.0 {
                        let mut s = String::new();
                        if write!(s, "{}", cpp).is_ok() {
                            return s.fmt(f)
                        }
                    }

                    format_symbol_name(fmt::Debug::fmt, self.bytes, f)
                }
            }
        } else {
            impl<'a> fmt::Debug for SymbolName<'a> {
                fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                    if let Some(ref s) = self.demangled {
                        s.fmt(f)
                    } else {
                        format_symbol_name(fmt::Debug::fmt, self.bytes, f)
                    }
                }
            }
        }
    }

    /// Attempt to reclaim that cached memory used to symbolicate addresses.
    ///
    /// This method will attempt to release any global data structures that have
    /// otherwise been cached globally or in the thread which typically represent
    /// parsed DWARF information or similar.
    ///
    /// # Caveats
    ///
    /// While this function is always available it doesn't actually do anything on
    /// most implementations. Libraries like dbghelp or libbacktrace do not provide
    /// facilities to deallocate state and manage the allocated memory. For now the
    /// `gimli-symbolize` feature of this crate is the only feature where this
    /// function has any effect.
    #[cfg(feature = "std")]
    pub fn clear_symbol_cache() {
        let _guard = crate::lock::lock();
        unsafe {
            clear_symbol_cache_imp();
        }
    }

    cfg_if::cfg_if! {
        if #[cfg(miri)] {
            mod noop;
            use self::noop::resolve as resolve_imp;
            use self::noop::Symbol as SymbolImp;
            #[allow(unused)]
            unsafe fn clear_symbol_cache_imp() {}
        } else if #[cfg(all(windows, target_env = "msvc", not(target_vendor = "uwp")))] {
            mod dbghelp;
            use self::dbghelp::resolve as resolve_imp;
            use self::dbghelp::Symbol as SymbolImp;
            unsafe fn clear_symbol_cache_imp() {}
        } else if #[cfg(all(
            feature = "libbacktrace",
            any(unix, all(windows, not(target_vendor = "uwp"), target_env = "gnu")),
            not(target_os = "fuchsia"),
            not(target_os = "emscripten"),
            not(target_env = "uclibc"),
        ))] {
            mod libbacktrace;
            use self::libbacktrace::resolve as resolve_imp;
            use self::libbacktrace::Symbol as SymbolImp;
            unsafe fn clear_symbol_cache_imp() {}
        } else if #[cfg(all(
            feature = "gimli-symbolize",
            any(unix, windows),
            not(target_vendor = "uwp"),
            not(target_os = "emscripten"),
        ))] {
            mod gimli;
            use self::gimli::resolve as resolve_imp;
            use self::gimli::Symbol as SymbolImp;
            use self::gimli::clear_symbol_cache as clear_symbol_cache_imp;
        } else {
            mod noop;
            use self::noop::resolve as resolve_imp;
            use self::noop::Symbol as SymbolImp;
            #[allow(unused)]
            unsafe fn clear_symbol_cache_imp() {}
        }
    }