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    // Copyright 2014-2015 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.

    use libc;

    use ffi::CStr;
    use io;
    use mem;
    use ptr;
    use sys::backtrace::BacktraceContext;
    use sys_common::backtrace::Frame;

    pub fn foreach_symbol_fileline<F>(frame: Frame,
                                      mut f: F,
                                      _: &BacktraceContext) -> io::Result<bool>
    where F: FnMut(&[u8], libc::c_int) -> io::Result<()>
    {
        // pcinfo may return an arbitrary number of file:line pairs,
        // in the order of stack trace (i.e. inlined calls first).
        // in order to avoid allocation, we stack-allocate a fixed size of entries.
        const FILELINE_SIZE: usize = 32;
        let mut fileline_buf = [(ptr::null(), -1); FILELINE_SIZE];
        let ret;
        let fileline_count = {
            let state = unsafe { init_state() };
            let mut fileline_win: &mut [FileLine] = &mut fileline_buf;
            let fileline_addr = &mut fileline_win as *mut &mut [FileLine];
            ret = unsafe {
                backtrace_pcinfo(state,
                                 frame.exact_position as libc::uintptr_t,
                                 pcinfo_cb,
                                 error_cb,
                                 fileline_addr as *mut libc::c_void)
            };
            FILELINE_SIZE - fileline_win.len()
        };
        if ret == 0 {
            for &(file, line) in &fileline_buf[..fileline_count] {
                if file.is_null() { continue; } // just to be sure
                let file = unsafe { CStr::from_ptr(file).to_bytes() };
                f(file, line)?;
            }
            Ok(fileline_count == FILELINE_SIZE)
        } else {
            Ok(false)
        }
    }

    /// Converts a pointer to symbol to its string value.
    pub fn resolve_symname<F>(frame: Frame,
                              callback: F,
                              _: &BacktraceContext) -> io::Result<()>
        where F: FnOnce(Option<&str>) -> io::Result<()>
    {
        let symname = {
            let state = unsafe { init_state() };
            if state.is_null() {
                None
            } else {
                let mut data = ptr::null();
                let data_addr = &mut data as *mut *const libc::c_char;
                let ret = unsafe {
                    backtrace_syminfo(state,
                                      frame.symbol_addr as libc::uintptr_t,
                                      syminfo_cb,
                                      error_cb,
                                      data_addr as *mut libc::c_void)
                };
                if ret == 0 || data.is_null() {
                    None
                } else {
                    unsafe {
                        CStr::from_ptr(data).to_str().ok()
                    }
                }
            }
        };
        callback(symname)
    }

    ////////////////////////////////////////////////////////////////////////
    // libbacktrace.h API
    ////////////////////////////////////////////////////////////////////////
    type backtrace_syminfo_callback =
    extern "C" fn(data: *mut libc::c_void,
                  pc: libc::uintptr_t,
                  symname: *const libc::c_char,
                  symval: libc::uintptr_t,
                  symsize: libc::uintptr_t);
    type backtrace_full_callback =
    extern "C" fn(data: *mut libc::c_void,
                  pc: libc::uintptr_t,
                  filename: *const libc::c_char,
                  lineno: libc::c_int,
                  function: *const libc::c_char) -> libc::c_int;
    type backtrace_error_callback =
    extern "C" fn(data: *mut libc::c_void,
                  msg: *const libc::c_char,
                  errnum: libc::c_int);
    enum backtrace_state {}

    extern {
        fn backtrace_create_state(filename: *const libc::c_char,
                                  threaded: libc::c_int,
                                  error: backtrace_error_callback,
                                  data: *mut libc::c_void)
            -> *mut backtrace_state;
        fn backtrace_syminfo(state: *mut backtrace_state,
                             addr: libc::uintptr_t,
                             cb: backtrace_syminfo_callback,
                             error: backtrace_error_callback,
                             data: *mut libc::c_void) -> libc::c_int;
        fn backtrace_pcinfo(state: *mut backtrace_state,
                            addr: libc::uintptr_t,
                            cb: backtrace_full_callback,
                            error: backtrace_error_callback,
                            data: *mut libc::c_void) -> libc::c_int;
    }

    ////////////////////////////////////////////////////////////////////////
    // helper callbacks
    ////////////////////////////////////////////////////////////////////////

    type FileLine = (*const libc::c_char, libc::c_int);

    extern fn error_cb(_data: *mut libc::c_void, _msg: *const libc::c_char,
                       _errnum: libc::c_int) {
        // do nothing for now
    }
    extern fn syminfo_cb(data: *mut libc::c_void,
                         _pc: libc::uintptr_t,
                         symname: *const libc::c_char,
                         _symval: libc::uintptr_t,
                         _symsize: libc::uintptr_t) {
        let slot = data as *mut *const libc::c_char;
        unsafe { *slot = symname; }
    }
    extern fn pcinfo_cb(data: *mut libc::c_void,
                        _pc: libc::uintptr_t,
                        filename: *const libc::c_char,
                        lineno: libc::c_int,
                        _function: *const libc::c_char) -> libc::c_int {
        if !filename.is_null() {
            let slot = data as *mut &mut [FileLine];
            let buffer = unsafe {ptr::read(slot)};

            // if the buffer is not full, add file:line to the buffer
            // and adjust the buffer for next possible calls to pcinfo_cb.
            if !buffer.is_empty() {
                buffer[0] = (filename, lineno);
                unsafe { ptr::write(slot, &mut buffer[1..]); }
            }
        }

        0
    }

    // The libbacktrace API supports creating a state, but it does not
    // support destroying a state. I personally take this to mean that a
    // state is meant to be created and then live forever.
    //
    // I would love to register an at_exit() handler which cleans up this
    // state, but libbacktrace provides no way to do so.
    //
    // With these constraints, this function has a statically cached state
    // that is calculated the first time this is requested. Remember that
    // backtracing all happens serially (one global lock).
    //
    // Things don't work so well on not-Linux since libbacktrace can't track
    // down that executable this is. We at one point used env::current_exe but
    // it turns out that there are some serious security issues with that
    // approach.
    //
    // Specifically, on certain platforms like BSDs, a malicious actor can cause
    // an arbitrary file to be placed at the path returned by current_exe.
    // libbacktrace does not behave defensively in the presence of ill-formed
    // DWARF information, and has been demonstrated to segfault in at least one
    // case. There is no evidence at the moment to suggest that a more carefully
    // constructed file can't cause arbitrary code execution. As a result of all
    // of this, we don't hint libbacktrace with the path to the current process.
    unsafe fn init_state() -> *mut backtrace_state {
        static mut STATE: *mut backtrace_state = ptr::null_mut();
        if !STATE.is_null() { return STATE  }

        let filename = match ::sys::backtrace::gnu::get_executable_filename() {
            Ok((filename, file)) => {
                // filename is purposely leaked here since libbacktrace requires
                // it to stay allocated permanently, file is also leaked so that
                // the file stays locked
                let filename_ptr = filename.as_ptr();
                mem::forget(filename);
                mem::forget(file);
                filename_ptr
            },
            Err(_) => ptr::null(),
        };

        STATE = backtrace_create_state(filename, 0, error_cb,
                                       ptr::null_mut());
        STATE
    }

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