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    #[cfg(feature = "std")]
    use super::{BacktraceFrame, BacktraceSymbol};
    use super::{BytesOrWideString, Frame, SymbolName};
    use core::ffi::c_void;
    use core::fmt;

    const HEX_WIDTH: usize = 2 + 2 * core::mem::size_of::<usize>();

    #[cfg(target_os = "fuchsia")]
    mod fuchsia;

    /// A formatter for backtraces.
    ///
    /// This type can be used to print a backtrace regardless of where the backtrace
    /// itself comes from. If you have a `Backtrace` type then its `Debug`
    /// implementation already uses this printing format.
    pub struct BacktraceFmt<'a, 'b> {
        fmt: &'a mut fmt::Formatter<'b>,
        frame_index: usize,
        format: PrintFmt,
        print_path:
            &'a mut (dyn FnMut(&mut fmt::Formatter<'_>, BytesOrWideString<'_>) -> fmt::Result + 'b),
    }

    /// The styles of printing that we can print
    #[derive(Copy, Clone, Eq, PartialEq)]
    pub enum PrintFmt {
        /// Prints a terser backtrace which ideally only contains relevant information
        Short,
        /// Prints a backtrace that contains all possible information
        Full,
        #[doc(hidden)]
        __Nonexhaustive,
    }

    impl<'a, 'b> BacktraceFmt<'a, 'b> {
        /// Create a new `BacktraceFmt` which will write output to the provided
        /// `fmt`.
        ///
        /// The `format` argument will control the style in which the backtrace is
        /// printed, and the `print_path` argument will be used to print the
        /// `BytesOrWideString` instances of filenames. This type itself doesn't do
        /// any printing of filenames, but this callback is required to do so.
        pub fn new(
            fmt: &'a mut fmt::Formatter<'b>,
            format: PrintFmt,
            print_path: &'a mut (dyn FnMut(&mut fmt::Formatter<'_>, BytesOrWideString<'_>) -> fmt::Result
                         + 'b),
        ) -> Self {
            BacktraceFmt {
                fmt,
                frame_index: 0,
                format,
                print_path,
            }
        }

        /// Prints a preamble for the backtrace about to be printed.
        ///
        /// This is required on some platforms for backtraces to be fully
        /// sumbolicated later, and otherwise this should just be the first method
        /// you call after creating a `BacktraceFmt`.
        pub fn add_context(&mut self) -> fmt::Result {
            #[cfg(target_os = "fuchsia")]
            fuchsia::print_dso_context(self.fmt)?;
            Ok(())
        }

        /// Adds a frame to the backtrace output.
        ///
        /// This commit returns an RAII instance of a `BacktraceFrameFmt` which can be used
        /// to actually print a frame, and on destruction it will increment the
        /// frame counter.
        pub fn frame(&mut self) -> BacktraceFrameFmt<'_, 'a, 'b> {
            BacktraceFrameFmt {
                fmt: self,
                symbol_index: 0,
            }
        }

        /// Completes the backtrace output.
        ///
        /// This is currently a no-op but is added for future compatibility with
        /// backtrace formats.
        pub fn finish(&mut self) -> fmt::Result {
            // Currently a no-op-- including this hook to allow for future additions.
            Ok(())
        }
    }

    /// A formatter for just one frame of a backtrace.
    ///
    /// This type is created by the `BacktraceFmt::frame` function.
    pub struct BacktraceFrameFmt<'fmt, 'a, 'b> {
        fmt: &'fmt mut BacktraceFmt<'a, 'b>,
        symbol_index: usize,
    }

    impl BacktraceFrameFmt<'_, '_, '_> {
        /// Prints a `BacktraceFrame` with this frame formatter.
        ///
        /// This will recusrively print all `BacktraceSymbol` instances within the
        /// `BacktraceFrame`.
        ///
        /// # 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")]
        pub fn backtrace_frame(&mut self, frame: &BacktraceFrame) -> fmt::Result {
            let symbols = frame.symbols();
            for symbol in symbols {
                self.backtrace_symbol(frame, symbol)?;
            }
            if symbols.is_empty() {
                self.print_raw(frame.ip(), None, None, None)?;
            }
            Ok(())
        }

        /// Prints a `BacktraceSymbol` within a `BacktraceFrame`.
        ///
        /// # 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")]
        pub fn backtrace_symbol(
            &mut self,
            frame: &BacktraceFrame,
            symbol: &BacktraceSymbol,
        ) -> fmt::Result {
            self.print_raw(
                frame.ip(),
                symbol.name(),
                // TODO: this isn't great that we don't end up printing anything
                // with non-utf8 filenames. Thankfully almost everything is utf8 so
                // this shouldn't be too too bad.
                symbol
                    .filename()
                    .and_then(|p| Some(BytesOrWideString::Bytes(p.to_str()?.as_bytes()))),
                symbol.lineno(),
            )?;
            Ok(())
        }

        /// Prints a raw traced `Frame` and `Symbol`, typically from within the raw
        /// callbacks of this crate.
        pub fn symbol(&mut self, frame: &Frame, symbol: &super::Symbol) -> fmt::Result {
            self.print_raw(
                frame.ip(),
                symbol.name(),
                symbol.filename_raw(),
                symbol.lineno(),
            )?;
            Ok(())
        }

        /// Adds a raw frame to the backtrace output.
        ///
        /// This method, unlike the previous, takes the raw arguments in case
        /// they're being source from different locations. Note that this may be
        /// called multiple times for one frame.
        pub fn print_raw(
            &mut self,
            frame_ip: *mut c_void,
            symbol_name: Option<SymbolName<'_>>,
            filename: Option<BytesOrWideString<'_>>,
            lineno: Option<u32>,
        ) -> fmt::Result {
            // Fuchsia is unable to symbolize within a process so it has a special
            // format which can be used to symbolize later. Print that instead of
            // printing addresses in our own format here.
            if cfg!(target_os = "fuchsia") {
                self.print_raw_fuchsia(frame_ip)?;
            } else {
                self.print_raw_generic(frame_ip, symbol_name, filename, lineno)?;
            }
            self.symbol_index += 1;
            Ok(())
        }

        #[allow(unused_mut)]
        fn print_raw_generic(
            &mut self,
            mut frame_ip: *mut c_void,
            symbol_name: Option<SymbolName<'_>>,
            filename: Option<BytesOrWideString<'_>>,
            lineno: Option<u32>,
        ) -> fmt::Result {
            // No need to print "null" frames, it basically just means that the
            // system backtrace was a bit eager to trace back super far.
            if let PrintFmt::Short = self.fmt.format {
                if frame_ip.is_null() {
                    return Ok(());
                }
            }

            // To reduce TCB size in Sgx enclave, we do not want to implement symbol
            // resolution functionality.  Rather, we can print the offset of the
            // address here, which could be later mapped to correct function.
            #[cfg(all(feature = "std", target_env = "sgx", target_vendor = "fortanix"))]
            {
                let image_base = std::os::fortanix_sgx::mem::image_base();
                frame_ip = usize::wrapping_sub(frame_ip as usize, image_base as _) as _;
            }

            // Print the index of the frame as well as the optional instruction
            // pointer of the frame. If we're beyond the first symbol of this frame
            // though we just print appropriate whitespace.
            if self.symbol_index == 0 {
                write!(self.fmt.fmt, "{:4}: ", self.fmt.frame_index)?;
                if let PrintFmt::Full = self.fmt.format {
                    write!(self.fmt.fmt, "{:1$?} - ", frame_ip, HEX_WIDTH)?;
                }
            } else {
                write!(self.fmt.fmt, "      ")?;
                if let PrintFmt::Full = self.fmt.format {
                    write!(self.fmt.fmt, "{:1$}", "", HEX_WIDTH + 3)?;
                }
            }

            // Next up write out the symbol name, using the alternate formatting for
            // more information if we're a full backtrace. Here we also handle
            // symbols which don't have a name,
            match (symbol_name, &self.fmt.format) {
                (Some(name), PrintFmt::Short) => write!(self.fmt.fmt, "{:#}", name)?,
                (Some(name), PrintFmt::Full) => write!(self.fmt.fmt, "{}", name)?,
                (None, _) | (_, PrintFmt::__Nonexhaustive) => write!(self.fmt.fmt, "<unknown>")?,
            }
            self.fmt.fmt.write_str("\n")?;

            // And last up, print out the filename/line number if they're available.
            if let (Some(file), Some(line)) = (filename, lineno) {
                self.print_fileline(file, line)?;
            }

            Ok(())
        }

        fn print_fileline(&mut self, file: BytesOrWideString<'_>, line: u32) -> fmt::Result {
            // Filename/line are printed on lines under the symbol name, so print
            // some appropriate whitespace to sort of right-align ourselves.
            if let PrintFmt::Full = self.fmt.format {
                write!(self.fmt.fmt, "{:1$}", "", HEX_WIDTH)?;
            }
            write!(self.fmt.fmt, "             at ")?;

            // Delegate to our internal callback to print the filename and then
            // print out the line number.
            (self.fmt.print_path)(self.fmt.fmt, file)?;
            write!(self.fmt.fmt, ":{}\n", line)?;
            Ok(())
        }

        fn print_raw_fuchsia(&mut self, frame_ip: *mut c_void) -> fmt::Result {
            // We only care about the first symbol of a frame
            if self.symbol_index == 0 {
                self.fmt.fmt.write_str("{{{bt:")?;
                write!(self.fmt.fmt, "{}:{:?}", self.fmt.frame_index, frame_ip)?;
                self.fmt.fmt.write_str("}}}\n")?;
            }
            Ok(())
        }
    }

    impl Drop for BacktraceFrameFmt<'_, '_, '_> {
        fn drop(&mut self) {
            self.fmt.frame_index += 1;
        }
    }