Refactor unix backtracing. NFC.

8 files changed, 681 insertions, 586 deletions

diff --git a/src/libstd/sys/unix/backtrace.rs b/src/libstd/sys/unix/backtrace.rs
deleted file mode 100644
index 853e745b8a1..00000000000
--- a/src/libstd/sys/unix/backtrace.rs
+++ /dev/null
@@ -1,586 +0,0 @@
-// 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.
-
-/// Backtrace support built on libgcc with some extra OS-specific support
-///
-/// Some methods of getting a backtrace:
-///
-/// * The backtrace() functions on unix. It turns out this doesn't work very
-///   well for green threads on OSX, and the address to symbol portion of it
-///   suffers problems that are described below.
-///
-/// * Using libunwind. This is more difficult than it sounds because libunwind
-///   isn't installed everywhere by default. It's also a bit of a hefty library,
-///   so possibly not the best option. When testing, libunwind was excellent at
-///   getting both accurate backtraces and accurate symbols across platforms.
-///   This route was not chosen in favor of the next option, however.
-///
-/// * We're already using libgcc_s for exceptions in rust (triggering thread
-///   unwinding and running destructors on the stack), and it turns out that it
-///   conveniently comes with a function that also gives us a backtrace. All of
-///   these functions look like _Unwind_*, but it's not quite the full
-///   repertoire of the libunwind API. Due to it already being in use, this was
-///   the chosen route of getting a backtrace.
-///
-/// After choosing libgcc_s for backtraces, the sad part is that it will only
-/// give us a stack trace of instruction pointers. Thankfully these instruction
-/// pointers are accurate (they work for green and native threads), but it's
-/// then up to us again to figure out how to translate these addresses to
-/// symbols. As with before, we have a few options. Before, that, a little bit
-/// of an interlude about symbols. This is my very limited knowledge about
-/// symbol tables, and this information is likely slightly wrong, but the
-/// general idea should be correct.
-///
-/// When talking about symbols, it's helpful to know a few things about where
-/// symbols are located. Some symbols are located in the dynamic symbol table
-/// of the executable which in theory means that they're available for dynamic
-/// linking and lookup. Other symbols end up only in the local symbol table of
-/// the file. This loosely corresponds to pub and priv functions in Rust.
-///
-/// Armed with this knowledge, we know that our solution for address to symbol
-/// translation will need to consult both the local and dynamic symbol tables.
-/// With that in mind, here's our options of translating an address to
-/// a symbol.
-///
-/// * Use dladdr(). The original backtrace()-based idea actually uses dladdr()
-///   behind the scenes to translate, and this is why backtrace() was not used.
-///   Conveniently, this method works fantastically on OSX. It appears dladdr()
-///   uses magic to consult the local symbol table, or we're putting everything
-///   in the dynamic symbol table anyway. Regardless, for OSX, this is the
-///   method used for translation. It's provided by the system and easy to do.o
-///
-///   Sadly, all other systems have a dladdr() implementation that does not
-///   consult the local symbol table. This means that most functions are blank
-///   because they don't have symbols. This means that we need another solution.
-///
-/// * Use unw_get_proc_name(). This is part of the libunwind api (not the
-///   libgcc_s version of the libunwind api), but involves taking a dependency
-///   to libunwind. We may pursue this route in the future if we bundle
-///   libunwind, but libunwind was unwieldy enough that it was not chosen at
-///   this time to provide this functionality.
-///
-/// * Shell out to a utility like `readelf`. Crazy though it may sound, it's a
-///   semi-reasonable solution. The stdlib already knows how to spawn processes,
-///   so in theory it could invoke readelf, parse the output, and consult the
-///   local/dynamic symbol tables from there. This ended up not getting chosen
-///   due to the craziness of the idea plus the advent of the next option.
-///
-/// * Use `libbacktrace`. It turns out that this is a small library bundled in
-///   the gcc repository which provides backtrace and symbol translation
-///   functionality. All we really need from it is the backtrace functionality,
-///   and we only really need this on everything that's not OSX, so this is the
-///   chosen route for now.
-///
-/// In summary, the current situation uses libgcc_s to get a trace of stack
-/// pointers, and we use dladdr() or libbacktrace to translate these addresses
-/// to symbols. This is a bit of a hokey implementation as-is, but it works for
-/// all unix platforms we support right now, so it at least gets the job done.
-
-use io::prelude::*;
-
-use ffi::CStr;
-use io;
-use libc;
-use str;
-use sync::StaticMutex;
-
-use sys_common::backtrace::*;
-
-/// As always - iOS on arm uses SjLj exceptions and
-/// _Unwind_Backtrace is even not available there. Still,
-/// backtraces could be extracted using a backtrace function,
-/// which thanks god is public
-///
-/// As mentioned in a huge comment block above, backtrace doesn't
-/// play well with green threads, so while it is extremely nice
-/// and simple to use it should be used only on iOS devices as the
-/// only viable option.
-#[cfg(all(target_os = "ios", target_arch = "arm"))]
-#[inline(never)]
-pub fn write(w: &mut Write) -> io::Result<()> {
-    use mem;
-
-    extern {
-        fn backtrace(buf: *mut *mut libc::c_void,
-                     sz: libc::c_int) -> libc::c_int;
-    }
-
-    // while it doesn't requires lock for work as everything is
-    // local, it still displays much nicer backtraces when a
-    // couple of threads panic simultaneously
-    static LOCK: StaticMutex = StaticMutex::new();
-    let _g = LOCK.lock();
-
-    try!(writeln!(w, "stack backtrace:"));
-    // 100 lines should be enough
-    const SIZE: usize = 100;
-    let mut buf: [*mut libc::c_void; SIZE] = unsafe { mem::zeroed() };
-    let cnt = unsafe { backtrace(buf.as_mut_ptr(), SIZE as libc::c_int) as usize};
-
-    // skipping the first one as it is write itself
-    for i in 1..cnt {
-        try!(print(w, i as isize, buf[i], buf[i]))
-    }
-    Ok(())
-}
-
-#[cfg(not(all(target_os = "ios", target_arch = "arm")))]
-#[inline(never)] // if we know this is a function call, we can skip it when
-                 // tracing
-pub fn write(w: &mut Write) -> io::Result<()> {
-    struct Context<'a> {
-        idx: isize,
-        writer: &'a mut (Write+'a),
-        last_error: Option<io::Error>,
-    }
-
-    // When using libbacktrace, we use some necessary global state, so we
-    // need to prevent more than one thread from entering this block. This
-    // is semi-reasonable in terms of printing anyway, and we know that all
-    // I/O done here is blocking I/O, not green I/O, so we don't have to
-    // worry about this being a native vs green mutex.
-    static LOCK: StaticMutex = StaticMutex::new();
-    let _g = LOCK.lock();
-
-    try!(writeln!(w, "stack backtrace:"));
-
-    let mut cx = Context { writer: w, last_error: None, idx: 0 };
-    return match unsafe {
-        uw::_Unwind_Backtrace(trace_fn,
-                              &mut cx as *mut Context as *mut libc::c_void)
-    } {
-        uw::_URC_NO_REASON => {
-            match cx.last_error {
-                Some(err) => Err(err),
-                None => Ok(())
-            }
-        }
-        _ => Ok(()),
-    };
-
-    extern fn trace_fn(ctx: *mut uw::_Unwind_Context,
-                       arg: *mut libc::c_void) -> uw::_Unwind_Reason_Code {
-        let cx: &mut Context = unsafe { &mut *(arg as *mut Context) };
-        let mut ip_before_insn = 0;
-        let mut ip = unsafe {
-            uw::_Unwind_GetIPInfo(ctx, &mut ip_before_insn) as *mut libc::c_void
-        };
-        if !ip.is_null() && ip_before_insn == 0 {
-            // this is a non-signaling frame, so `ip` refers to the address
-            // after the calling instruction. account for that.
-            ip = (ip as usize - 1) as *mut _;
-        }
-
-        // dladdr() on osx gets whiny when we use FindEnclosingFunction, and
-        // it appears to work fine without it, so we only use
-        // FindEnclosingFunction on non-osx platforms. In doing so, we get a
-        // slightly more accurate stack trace in the process.
-        //
-        // This is often because panic involves the last instruction of a
-        // function being "call std::rt::begin_unwind", with no ret
-        // instructions after it. This means that the return instruction
-        // pointer points *outside* of the calling function, and by
-        // unwinding it we go back to the original function.
-        let symaddr = if cfg!(target_os = "macos") || cfg!(target_os = "ios") {
-            ip
-        } else {
-            unsafe { uw::_Unwind_FindEnclosingFunction(ip) }
-        };
-
-        // Don't print out the first few frames (they're not user frames)
-        cx.idx += 1;
-        if cx.idx <= 0 { return uw::_URC_NO_REASON }
-        // Don't print ginormous backtraces
-        if cx.idx > 100 {
-            match write!(cx.writer, " ... <frames omitted>\n") {
-                Ok(()) => {}
-                Err(e) => { cx.last_error = Some(e); }
-            }
-            return uw::_URC_FAILURE
-        }
-
-        // Once we hit an error, stop trying to print more frames
-        if cx.last_error.is_some() { return uw::_URC_FAILURE }
-
-        match print(cx.writer, cx.idx, ip, symaddr) {
-            Ok(()) => {}
-            Err(e) => { cx.last_error = Some(e); }
-        }
-
-        // keep going
-        return uw::_URC_NO_REASON
-    }
-}
-
-#[cfg(any(target_os = "macos", target_os = "ios"))]
-fn print(w: &mut Write, idx: isize, addr: *mut libc::c_void,
-         _symaddr: *mut libc::c_void) -> io::Result<()> {
-    use intrinsics;
-    #[repr(C)]
-    struct Dl_info {
-        dli_fname: *const libc::c_char,
-        dli_fbase: *mut libc::c_void,
-        dli_sname: *const libc::c_char,
-        dli_saddr: *mut libc::c_void,
-    }
-    extern {
-        fn dladdr(addr: *const libc::c_void,
-                  info: *mut Dl_info) -> libc::c_int;
-    }
-
-    let mut info: Dl_info = unsafe { intrinsics::init() };
-    if unsafe { dladdr(addr, &mut info) == 0 } {
-        output(w, idx,addr, None)
-    } else {
-        output(w, idx, addr, Some(unsafe {
-            CStr::from_ptr(info.dli_sname).to_bytes()
-        }))
-    }
-}
-
-#[cfg(not(any(target_os = "macos", target_os = "ios")))]
-fn print(w: &mut Write, idx: isize, addr: *mut libc::c_void,
-         symaddr: *mut libc::c_void) -> io::Result<()> {
-    use env;
-    use os::unix::prelude::*;
-    use ptr;
-
-    ////////////////////////////////////////////////////////////////////////
-    // 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 {}
-    #[link(name = "backtrace", kind = "static")]
-    #[cfg(not(test))]
-    extern {}
-
-    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).
-    //
-    // An additionally oddity in this function is that we initialize the
-    // filename via self_exe_name() to pass to libbacktrace. It turns out
-    // that on Linux libbacktrace seamlessly gets the filename of the
-    // current executable, but this fails on freebsd. by always providing
-    // it, we make sure that libbacktrace never has a reason to not look up
-    // the symbols. The libbacktrace API also states that the filename must
-    // be in "permanent memory", so we copy it to a static and then use the
-    // static as the pointer.
-    //
-    // FIXME: We also call self_exe_name() on DragonFly BSD. I haven't
-    //        tested if this is required or not.
-    unsafe fn init_state() -> *mut backtrace_state {
-        static mut STATE: *mut backtrace_state = 0 as *mut backtrace_state;
-        static mut LAST_FILENAME: [libc::c_char; 256] = [0; 256];
-        if !STATE.is_null() { return STATE }
-        let selfname = if cfg!(target_os = "freebsd") ||
-                          cfg!(target_os = "dragonfly") ||
-                          cfg!(target_os = "bitrig") ||
-                          cfg!(target_os = "netbsd") ||
-                          cfg!(target_os = "openbsd") {
-            env::current_exe().ok()
-        } else {
-            None
-        };
-        let filename = match selfname {
-            Some(path) => {
-                let bytes = path.as_os_str().as_bytes();
-                if bytes.len() < LAST_FILENAME.len() {
-                    let i = bytes.iter();
-                    for (slot, val) in LAST_FILENAME.iter_mut().zip(i) {
-                        *slot = *val as libc::c_char;
-                    }
-                    LAST_FILENAME.as_ptr()
-                } else {
-                    ptr::null()
-                }
-            }
-            None => ptr::null(),
-        };
-        STATE = backtrace_create_state(filename, 0, error_cb,
-                                       ptr::null_mut());
-        return STATE
-    }
-
-    ////////////////////////////////////////////////////////////////////////
-    // translation
-    ////////////////////////////////////////////////////////////////////////
-
-    // backtrace errors are currently swept under the rug, only I/O
-    // errors are reported
-    let state = unsafe { init_state() };
-    if state.is_null() {
-        return output(w, idx, addr, None)
-    }
-    let mut data = ptr::null();
-    let data_addr = &mut data as *mut *const libc::c_char;
-    let ret = unsafe {
-        backtrace_syminfo(state, symaddr as libc::uintptr_t,
-                          syminfo_cb, error_cb,
-                          data_addr as *mut libc::c_void)
-    };
-    if ret == 0 || data.is_null() {
-        try!(output(w, idx, addr, None));
-    } else {
-        try!(output(w, idx, addr, Some(unsafe { CStr::from_ptr(data).to_bytes() })));
-    }
-
-    // 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 mut fileline_win: &mut [FileLine] = &mut fileline_buf;
-        let fileline_addr = &mut fileline_win as *mut &mut [FileLine];
-        ret = unsafe {
-            backtrace_pcinfo(state, addr as libc::uintptr_t,
-                             pcinfo_cb, error_cb,
-                             fileline_addr as *mut libc::c_void)
-        };
-        fileline_count = FILELINE_SIZE - fileline_win.len();
-    }
-    if ret == 0 {
-        for (i, &(file, line)) in fileline_buf[..fileline_count].iter().enumerate() {
-            if file.is_null() { continue; } // just to be sure
-            let file = unsafe { CStr::from_ptr(file).to_bytes() };
-            try!(output_fileline(w, file, line, i == FILELINE_SIZE - 1));
-        }
-    }
-
-    Ok(())
-}
-
-// Finally, after all that work above, we can emit a symbol.
-fn output(w: &mut Write, idx: isize, addr: *mut libc::c_void,
-          s: Option<&[u8]>) -> io::Result<()> {
-    try!(write!(w, "  {:2}: {:2$?} - ", idx, addr, HEX_WIDTH));
-    match s.and_then(|s| str::from_utf8(s).ok()) {
-        Some(string) => try!(demangle(w, string)),
-        None => try!(write!(w, "<unknown>")),
-    }
-    w.write_all(&['\n' as u8])
-}
-
-#[allow(dead_code)]
-fn output_fileline(w: &mut Write, file: &[u8], line: libc::c_int,
-                   more: bool) -> io::Result<()> {
-    let file = str::from_utf8(file).unwrap_or("<unknown>");
-    // prior line: "  ##: {:2$} - func"
-    try!(write!(w, "      {:3$}at {}:{}", "", file, line, HEX_WIDTH));
-    if more {
-        try!(write!(w, " <... and possibly more>"));
-    }
-    w.write_all(&['\n' as u8])
-}
-
-/// Unwind library interface used for backtraces
-///
-/// Note that dead code is allowed as here are just bindings
-/// iOS doesn't use all of them it but adding more
-/// platform-specific configs pollutes the code too much
-#[allow(non_camel_case_types)]
-#[allow(non_snake_case)]
-#[allow(dead_code)]
-mod uw {
-    pub use self::_Unwind_Reason_Code::*;
-
-    use libc;
-
-    #[repr(C)]
-    pub enum _Unwind_Reason_Code {
-        _URC_NO_REASON = 0,
-        _URC_FOREIGN_EXCEPTION_CAUGHT = 1,
-        _URC_FATAL_PHASE2_ERROR = 2,
-        _URC_FATAL_PHASE1_ERROR = 3,
-        _URC_NORMAL_STOP = 4,
-        _URC_END_OF_STACK = 5,
-        _URC_HANDLER_FOUND = 6,
-        _URC_INSTALL_CONTEXT = 7,
-        _URC_CONTINUE_UNWIND = 8,
-        _URC_FAILURE = 9, // used only by ARM EABI
-    }
-
-    pub enum _Unwind_Context {}
-
-    pub type _Unwind_Trace_Fn =
-            extern fn(ctx: *mut _Unwind_Context,
-                      arg: *mut libc::c_void) -> _Unwind_Reason_Code;
-
-    extern {
-        // No native _Unwind_Backtrace on iOS
-        #[cfg(not(all(target_os = "ios", target_arch = "arm")))]
-        pub fn _Unwind_Backtrace(trace: _Unwind_Trace_Fn,
-                                 trace_argument: *mut libc::c_void)
-                    -> _Unwind_Reason_Code;
-
-        // available since GCC 4.2.0, should be fine for our purpose
-        #[cfg(all(not(all(target_os = "android", target_arch = "arm")),
-                  not(all(target_os = "linux", target_arch = "arm"))))]
-        pub fn _Unwind_GetIPInfo(ctx: *mut _Unwind_Context,
-                                 ip_before_insn: *mut libc::c_int)
-                    -> libc::uintptr_t;
-
-        #[cfg(all(not(target_os = "android"),
-                  not(all(target_os = "linux", target_arch = "arm"))))]
-        pub fn _Unwind_FindEnclosingFunction(pc: *mut libc::c_void)
-            -> *mut libc::c_void;
-    }
-
-    // On android, the function _Unwind_GetIP is a macro, and this is the
-    // expansion of the macro. This is all copy/pasted directly from the
-    // header file with the definition of _Unwind_GetIP.
-    #[cfg(any(all(target_os = "android", target_arch = "arm"),
-              all(target_os = "linux", target_arch = "arm")))]
-    pub unsafe fn _Unwind_GetIP(ctx: *mut _Unwind_Context) -> libc::uintptr_t {
-        #[repr(C)]
-        enum _Unwind_VRS_Result {
-            _UVRSR_OK = 0,
-            _UVRSR_NOT_IMPLEMENTED = 1,
-            _UVRSR_FAILED = 2,
-        }
-        #[repr(C)]
-        enum _Unwind_VRS_RegClass {
-            _UVRSC_CORE = 0,
-            _UVRSC_VFP = 1,
-            _UVRSC_FPA = 2,
-            _UVRSC_WMMXD = 3,
-            _UVRSC_WMMXC = 4,
-        }
-        #[repr(C)]
-        enum _Unwind_VRS_DataRepresentation {
-            _UVRSD_UINT32 = 0,
-            _UVRSD_VFPX = 1,
-            _UVRSD_FPAX = 2,
-            _UVRSD_UINT64 = 3,
-            _UVRSD_FLOAT = 4,
-            _UVRSD_DOUBLE = 5,
-        }
-
-        type _Unwind_Word = libc::c_uint;
-        extern {
-            fn _Unwind_VRS_Get(ctx: *mut _Unwind_Context,
-                               klass: _Unwind_VRS_RegClass,
-                               word: _Unwind_Word,
-                               repr: _Unwind_VRS_DataRepresentation,
-                               data: *mut libc::c_void)
-                -> _Unwind_VRS_Result;
-        }
-
-        let mut val: _Unwind_Word = 0;
-        let ptr = &mut val as *mut _Unwind_Word;
-        let _ = _Unwind_VRS_Get(ctx, _Unwind_VRS_RegClass::_UVRSC_CORE, 15,
-                                _Unwind_VRS_DataRepresentation::_UVRSD_UINT32,
-                                ptr as *mut libc::c_void);
-        (val & !1) as libc::uintptr_t
-    }
-
-    // This function doesn't exist on Android or ARM/Linux, so make it same
-    // to _Unwind_GetIP
-    #[cfg(any(all(target_os = "android", target_arch = "arm"),
-              all(target_os = "linux", target_arch = "arm")))]
-    pub unsafe fn _Unwind_GetIPInfo(ctx: *mut _Unwind_Context,
-                                    ip_before_insn: *mut libc::c_int)
-        -> libc::uintptr_t
-    {
-        *ip_before_insn = 0;
-        _Unwind_GetIP(ctx)
-    }
-
-    // This function also doesn't exist on Android or ARM/Linux, so make it
-    // a no-op
-    #[cfg(any(target_os = "android",
-              all(target_os = "linux", target_arch = "arm")))]
-    pub unsafe fn _Unwind_FindEnclosingFunction(pc: *mut libc::c_void)
-        -> *mut libc::c_void
-    {
-        pc
-    }
-}
diff --git a/src/libstd/sys/unix/backtrace/mod.rs b/src/libstd/sys/unix/backtrace/mod.rs
new file mode 100644
index 00000000000..80dcffd0e63
--- /dev/null
+++ b/src/libstd/sys/unix/backtrace/mod.rs
@@ -0,0 +1,119 @@
+// Copyright 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.
+
+/// Backtrace support built on libgcc with some extra OS-specific support
+///
+/// Some methods of getting a backtrace:
+///
+/// * The backtrace() functions on unix. It turns out this doesn't work very
+///   well for green threads on OSX, and the address to symbol portion of it
+///   suffers problems that are described below.
+///
+/// * Using libunwind. This is more difficult than it sounds because libunwind
+///   isn't installed everywhere by default. It's also a bit of a hefty library,
+///   so possibly not the best option. When testing, libunwind was excellent at
+///   getting both accurate backtraces and accurate symbols across platforms.
+///   This route was not chosen in favor of the next option, however.
+///
+/// * We're already using libgcc_s for exceptions in rust (triggering thread
+///   unwinding and running destructors on the stack), and it turns out that it
+///   conveniently comes with a function that also gives us a backtrace. All of
+///   these functions look like _Unwind_*, but it's not quite the full
+///   repertoire of the libunwind API. Due to it already being in use, this was
+///   the chosen route of getting a backtrace.
+///
+/// After choosing libgcc_s for backtraces, the sad part is that it will only
+/// give us a stack trace of instruction pointers. Thankfully these instruction
+/// pointers are accurate (they work for green and native threads), but it's
+/// then up to us again to figure out how to translate these addresses to
+/// symbols. As with before, we have a few options. Before, that, a little bit
+/// of an interlude about symbols. This is my very limited knowledge about
+/// symbol tables, and this information is likely slightly wrong, but the
+/// general idea should be correct.
+///
+/// When talking about symbols, it's helpful to know a few things about where
+/// symbols are located. Some symbols are located in the dynamic symbol table
+/// of the executable which in theory means that they're available for dynamic
+/// linking and lookup. Other symbols end up only in the local symbol table of
+/// the file. This loosely corresponds to pub and priv functions in Rust.
+///
+/// Armed with this knowledge, we know that our solution for address to symbol
+/// translation will need to consult both the local and dynamic symbol tables.
+/// With that in mind, here's our options of translating an address to
+/// a symbol.
+///
+/// * Use dladdr(). The original backtrace()-based idea actually uses dladdr()
+///   behind the scenes to translate, and this is why backtrace() was not used.
+///   Conveniently, this method works fantastically on OSX. It appears dladdr()
+///   uses magic to consult the local symbol table, or we're putting everything
+///   in the dynamic symbol table anyway. Regardless, for OSX, this is the
+///   method used for translation. It's provided by the system and easy to do.o
+///
+///   Sadly, all other systems have a dladdr() implementation that does not
+///   consult the local symbol table. This means that most functions are blank
+///   because they don't have symbols. This means that we need another solution.
+///
+/// * Use unw_get_proc_name(). This is part of the libunwind api (not the
+///   libgcc_s version of the libunwind api), but involves taking a dependency
+///   to libunwind. We may pursue this route in the future if we bundle
+///   libunwind, but libunwind was unwieldy enough that it was not chosen at
+///   this time to provide this functionality.
+///
+/// * Shell out to a utility like `readelf`. Crazy though it may sound, it's a
+///   semi-reasonable solution. The stdlib already knows how to spawn processes,
+///   so in theory it could invoke readelf, parse the output, and consult the
+///   local/dynamic symbol tables from there. This ended up not getting chosen
+///   due to the craziness of the idea plus the advent of the next option.
+///
+/// * Use `libbacktrace`. It turns out that this is a small library bundled in
+///   the gcc repository which provides backtrace and symbol translation
+///   functionality. All we really need from it is the backtrace functionality,
+///   and we only really need this on everything that's not OSX, so this is the
+///   chosen route for now.
+///
+/// In summary, the current situation uses libgcc_s to get a trace of stack
+/// pointers, and we use dladdr() or libbacktrace to translate these addresses
+/// to symbols. This is a bit of a hokey implementation as-is, but it works for
+/// all unix platforms we support right now, so it at least gets the job done.
+
+pub use self::tracing::write;
+
+use io;
+use io::prelude::*;
+use libc;
+use str;
+
+use sys_common::backtrace::{demangle, HEX_WIDTH};
+
+// tracing impls:
+mod tracing;
+// symbol resolvers:
+mod printing;
+
+pub fn output(w: &mut Write, idx: isize, addr: *mut libc::c_void,
+              s: Option<&[u8]>) -> io::Result<()> {
+    try!(write!(w, "  {:2}: {:2$?} - ", idx, addr, HEX_WIDTH));
+    match s.and_then(|s| str::from_utf8(s).ok()) {
+        Some(string) => try!(demangle(w, string)),
+        None => try!(write!(w, "<unknown>")),
+    }
+    w.write_all(&['\n' as u8])
+}
+
+pub fn output_fileline(w: &mut Write, file: &[u8], line: libc::c_int,
+                       more: bool) -> io::Result<()> {
+    let file = str::from_utf8(file).unwrap_or("<unknown>");
+    // prior line: "  ##: {:2$} - func"
+    try!(write!(w, "      {:3$}at {}:{}", "", file, line, HEX_WIDTH));
+    if more {
+        try!(write!(w, " <... and possibly more>"));
+    }
+    w.write_all(&['\n' as u8])
+}
diff --git a/src/libstd/sys/unix/backtrace/printing/dladdr.rs b/src/libstd/sys/unix/backtrace/printing/dladdr.rs
new file mode 100644
index 00000000000..fc7894a97b0
--- /dev/null
+++ b/src/libstd/sys/unix/backtrace/printing/dladdr.rs
@@ -0,0 +1,35 @@
+// 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.
+
+pub fn print(w: &mut Write, idx: isize, addr: *mut libc::c_void,
+             _symaddr: *mut libc::c_void) -> io::Result<()> {
+    use sys::backtrace::{output};
+    use intrinsics;
+    #[repr(C)]
+    struct Dl_info {
+        dli_fname: *const libc::c_char,
+        dli_fbase: *mut libc::c_void,
+        dli_sname: *const libc::c_char,
+        dli_saddr: *mut libc::c_void,
+    }
+    extern {
+        fn dladdr(addr: *const libc::c_void,
+                  info: *mut Dl_info) -> libc::c_int;
+    }
+
+    let mut info: Dl_info = unsafe { intrinsics::init() };
+    if unsafe { dladdr(addr, &mut info) == 0 } {
+        output(w, idx,addr, None)
+    } else {
+        output(w, idx, addr, Some(unsafe {
+            CStr::from_ptr(info.dli_sname).to_bytes()
+        }))
+    }
+}
diff --git a/src/libstd/sys/unix/backtrace/printing/libbacktrace.rs b/src/libstd/sys/unix/backtrace/printing/libbacktrace.rs
new file mode 100644
index 00000000000..711e241161d
--- /dev/null
+++ b/src/libstd/sys/unix/backtrace/printing/libbacktrace.rs
@@ -0,0 +1,206 @@
+// 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 io;
+use io::prelude::*;
+use libc;
+
+use sys::backtrace::{output, output_fileline};
+pub fn print(w: &mut Write, idx: isize, addr: *mut libc::c_void,
+             symaddr: *mut libc::c_void) -> io::Result<()> {
+    use env;
+    use ffi::CStr;
+    use os::unix::prelude::*;
+    use ptr;
+
+    ////////////////////////////////////////////////////////////////////////
+    // 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 {}
+    #[link(name = "backtrace", kind = "static")]
+    #[cfg(not(test))]
+    extern {}
+
+    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).
+    //
+    // An additionally oddity in this function is that we initialize the
+    // filename via self_exe_name() to pass to libbacktrace. It turns out
+    // that on Linux libbacktrace seamlessly gets the filename of the
+    // current executable, but this fails on freebsd. by always providing
+    // it, we make sure that libbacktrace never has a reason to not look up
+    // the symbols. The libbacktrace API also states that the filename must
+    // be in "permanent memory", so we copy it to a static and then use the
+    // static as the pointer.
+    //
+    // FIXME: We also call self_exe_name() on DragonFly BSD. I haven't
+    //        tested if this is required or not.
+    unsafe fn init_state() -> *mut backtrace_state {
+        static mut STATE: *mut backtrace_state = 0 as *mut backtrace_state;
+        static mut LAST_FILENAME: [libc::c_char; 256] = [0; 256];
+        if !STATE.is_null() { return STATE }
+        let selfname = if cfg!(target_os = "freebsd") ||
+            cfg!(target_os = "dragonfly") ||
+            cfg!(target_os = "bitrig") ||
+            cfg!(target_os = "openbsd") {
+                env::current_exe().ok()
+            } else {
+                None
+            };
+        let filename = match selfname {
+            Some(path) => {
+                let bytes = path.as_os_str().as_bytes();
+                if bytes.len() < LAST_FILENAME.len() {
+                    let i = bytes.iter();
+                    for (slot, val) in LAST_FILENAME.iter_mut().zip(i) {
+                        *slot = *val as libc::c_char;
+                    }
+                    LAST_FILENAME.as_ptr()
+                } else {
+                    ptr::null()
+                }
+            }
+            None => ptr::null(),
+        };
+        STATE = backtrace_create_state(filename, 0, error_cb,
+                                       ptr::null_mut());
+        return STATE
+    }
+
+    ////////////////////////////////////////////////////////////////////////
+    // translation
+    ////////////////////////////////////////////////////////////////////////
+
+    // backtrace errors are currently swept under the rug, only I/O
+    // errors are reported
+    let state = unsafe { init_state() };
+    if state.is_null() {
+        return output(w, idx, addr, None)
+    }
+    let mut data = ptr::null();
+    let data_addr = &mut data as *mut *const libc::c_char;
+    let ret = unsafe {
+        backtrace_syminfo(state, symaddr as libc::uintptr_t,
+                          syminfo_cb, error_cb,
+                          data_addr as *mut libc::c_void)
+    };
+    if ret == 0 || data.is_null() {
+        try!(output(w, idx, addr, None));
+    } else {
+        try!(output(w, idx, addr, Some(unsafe { CStr::from_ptr(data).to_bytes() })));
+    }
+
+    // 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 mut fileline_win: &mut [FileLine] = &mut fileline_buf;
+        let fileline_addr = &mut fileline_win as *mut &mut [FileLine];
+        ret = unsafe {
+            backtrace_pcinfo(state, addr as libc::uintptr_t,
+                             pcinfo_cb, error_cb,
+                             fileline_addr as *mut libc::c_void)
+        };
+        fileline_count = FILELINE_SIZE - fileline_win.len();
+    }
+    if ret == 0 {
+        for (i, &(file, line)) in fileline_buf[..fileline_count].iter().enumerate() {
+            if file.is_null() { continue; } // just to be sure
+            let file = unsafe { CStr::from_ptr(file).to_bytes() };
+            try!(output_fileline(w, file, line, i == FILELINE_SIZE - 1));
+        }
+    }
+
+    Ok(())
+}
diff --git a/src/libstd/sys/unix/backtrace/printing/mod.rs b/src/libstd/sys/unix/backtrace/printing/mod.rs
new file mode 100644
index 00000000000..a3bd45566f1
--- /dev/null
+++ b/src/libstd/sys/unix/backtrace/printing/mod.rs
@@ -0,0 +1,19 @@
+// 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.
+
+pub use self::imp::*;
+
+#[cfg(any(target_os = "macos", target_os = "ios"))]
+#[path = "dladdr.rs"]
+mod imp;
+
+#[cfg(not(any(target_os = "macos", target_os = "ios")))]
+#[path = "libbacktrace.rs"]
+mod imp;
diff --git a/src/libstd/sys/unix/backtrace/tracing/backtrace_fn.rs b/src/libstd/sys/unix/backtrace/tracing/backtrace_fn.rs
new file mode 100644
index 00000000000..2865abb254c
--- /dev/null
+++ b/src/libstd/sys/unix/backtrace/tracing/backtrace_fn.rs
@@ -0,0 +1,57 @@
+// 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.
+
+/// As always - iOS on arm uses SjLj exceptions and
+/// _Unwind_Backtrace is even not available there. Still,
+/// backtraces could be extracted using a backtrace function,
+/// which thanks god is public
+///
+/// As mentioned in a huge comment block in `super::super`, backtrace
+/// doesn't play well with green threads, so while it is extremely nice and
+/// simple to use it should be used only on iOS devices as the only viable
+/// option.
+
+use io;
+use io::prelude::*;
+use iter::Iterator;
+use libc;
+use mem;
+use result::Result::Ok;
+use sync::StaticMutex;
+
+use super::printer::print;
+
+#[inline(never)]
+pub fn write(w: &mut Write) -> io::Result<()> {
+    use mem;
+
+    extern {
+        fn backtrace(buf: *mut *mut libc::c_void,
+                     sz: libc::c_int) -> libc::c_int;
+    }
+
+    // while it doesn't requires lock for work as everything is
+    // local, it still displays much nicer backtraces when a
+    // couple of threads panic simultaneously
+    static LOCK: StaticMutex = StaticMutex::new();
+    let _g = LOCK.lock();
+
+    try!(writeln!(w, "stack backtrace:"));
+    // 100 lines should be enough
+    const SIZE: usize = 100;
+    let mut buf: [*mut libc::c_void; SIZE] = unsafe { mem::zeroed() };
+    let cnt = unsafe { backtrace(buf.as_mut_ptr(), SIZE as libc::c_int) as usize};
+
+    // skipping the first one as it is write itself
+    for i in 1..cnt {
+        try!(print(w, i as isize, buf[i], buf[i]))
+    }
+    Ok(())
+}
diff --git a/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs b/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs
new file mode 100644
index 00000000000..cdaf69c4882
--- /dev/null
+++ b/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs
@@ -0,0 +1,227 @@
+// 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 io;
+use io::prelude::*;
+use libc;
+use mem;
+use sync::StaticMutex;
+
+use super::super::printing::print;
+
+#[inline(never)] // if we know this is a function call, we can skip it when
+                 // tracing
+pub fn write(w: &mut Write) -> io::Result<()> {
+    struct Context<'a> {
+        idx: isize,
+        writer: &'a mut (Write+'a),
+        last_error: Option<io::Error>,
+    }
+
+    // When using libbacktrace, we use some necessary global state, so we
+    // need to prevent more than one thread from entering this block. This
+    // is semi-reasonable in terms of printing anyway, and we know that all
+    // I/O done here is blocking I/O, not green I/O, so we don't have to
+    // worry about this being a native vs green mutex.
+    static LOCK: StaticMutex = StaticMutex::new();
+    let _g = LOCK.lock();
+
+    try!(writeln!(w, "stack backtrace:"));
+
+    let mut cx = Context { writer: w, last_error: None, idx: 0 };
+    return match unsafe {
+        uw::_Unwind_Backtrace(trace_fn,
+                              &mut cx as *mut Context as *mut libc::c_void)
+    } {
+        uw::_URC_NO_REASON => {
+            match cx.last_error {
+                Some(err) => Err(err),
+                None => Ok(())
+            }
+        }
+        _ => Ok(()),
+    };
+
+    extern fn trace_fn(ctx: *mut uw::_Unwind_Context,
+                       arg: *mut libc::c_void) -> uw::_Unwind_Reason_Code {
+        let cx: &mut Context = unsafe { mem::transmute(arg) };
+        let mut ip_before_insn = 0;
+        let mut ip = unsafe {
+            uw::_Unwind_GetIPInfo(ctx, &mut ip_before_insn) as *mut libc::c_void
+        };
+        if !ip.is_null() && ip_before_insn == 0 {
+            // this is a non-signaling frame, so `ip` refers to the address
+            // after the calling instruction. account for that.
+            ip = (ip as usize - 1) as *mut _;
+        }
+
+        // dladdr() on osx gets whiny when we use FindEnclosingFunction, and
+        // it appears to work fine without it, so we only use
+        // FindEnclosingFunction on non-osx platforms. In doing so, we get a
+        // slightly more accurate stack trace in the process.
+        //
+        // This is often because panic involves the last instruction of a
+        // function being "call std::rt::begin_unwind", with no ret
+        // instructions after it. This means that the return instruction
+        // pointer points *outside* of the calling function, and by
+        // unwinding it we go back to the original function.
+        let symaddr = if cfg!(target_os = "macos") || cfg!(target_os = "ios") {
+            ip
+        } else {
+            unsafe { uw::_Unwind_FindEnclosingFunction(ip) }
+        };
+
+        // Don't print out the first few frames (they're not user frames)
+        cx.idx += 1;
+        if cx.idx <= 0 { return uw::_URC_NO_REASON }
+        // Don't print ginormous backtraces
+        if cx.idx > 100 {
+            match write!(cx.writer, " ... <frames omitted>\n") {
+                Ok(()) => {}
+                Err(e) => { cx.last_error = Some(e); }
+            }
+            return uw::_URC_FAILURE
+        }
+
+        // Once we hit an error, stop trying to print more frames
+        if cx.last_error.is_some() { return uw::_URC_FAILURE }
+
+        match print(cx.writer, cx.idx, ip, symaddr) {
+            Ok(()) => {}
+            Err(e) => { cx.last_error = Some(e); }
+        }
+
+        // keep going
+        return uw::_URC_NO_REASON
+    }
+}
+
+/// Unwind library interface used for backtraces
+///
+/// Note that dead code is allowed as here are just bindings
+/// iOS doesn't use all of them it but adding more
+/// platform-specific configs pollutes the code too much
+#[allow(non_camel_case_types)]
+#[allow(non_snake_case)]
+mod uw {
+    pub use self::_Unwind_Reason_Code::*;
+
+    use libc;
+
+    #[repr(C)]
+    pub enum _Unwind_Reason_Code {
+        _URC_NO_REASON = 0,
+        _URC_FOREIGN_EXCEPTION_CAUGHT = 1,
+        _URC_FATAL_PHASE2_ERROR = 2,
+        _URC_FATAL_PHASE1_ERROR = 3,
+        _URC_NORMAL_STOP = 4,
+        _URC_END_OF_STACK = 5,
+        _URC_HANDLER_FOUND = 6,
+        _URC_INSTALL_CONTEXT = 7,
+        _URC_CONTINUE_UNWIND = 8,
+        _URC_FAILURE = 9, // used only by ARM EABI
+    }
+
+    pub enum _Unwind_Context {}
+
+    pub type _Unwind_Trace_Fn =
+            extern fn(ctx: *mut _Unwind_Context,
+                      arg: *mut libc::c_void) -> _Unwind_Reason_Code;
+
+    extern {
+        // No native _Unwind_Backtrace on iOS
+        #[cfg(not(all(target_os = "ios", target_arch = "arm")))]
+        pub fn _Unwind_Backtrace(trace: _Unwind_Trace_Fn,
+                                 trace_argument: *mut libc::c_void)
+                    -> _Unwind_Reason_Code;
+
+        // available since GCC 4.2.0, should be fine for our purpose
+        #[cfg(all(not(all(target_os = "android", target_arch = "arm")),
+                  not(all(target_os = "linux", target_arch = "arm"))))]
+        pub fn _Unwind_GetIPInfo(ctx: *mut _Unwind_Context,
+                                 ip_before_insn: *mut libc::c_int)
+                    -> libc::uintptr_t;
+
+        #[cfg(all(not(target_os = "android"),
+                  not(all(target_os = "linux", target_arch = "arm"))))]
+        pub fn _Unwind_FindEnclosingFunction(pc: *mut libc::c_void)
+            -> *mut libc::c_void;
+    }
+
+    // On android, the function _Unwind_GetIP is a macro, and this is the
+    // expansion of the macro. This is all copy/pasted directly from the
+    // header file with the definition of _Unwind_GetIP.
+    #[cfg(any(all(target_os = "android", target_arch = "arm"),
+              all(target_os = "linux", target_arch = "arm")))]
+    pub unsafe fn _Unwind_GetIP(ctx: *mut _Unwind_Context) -> libc::uintptr_t {
+        #[repr(C)]
+        enum _Unwind_VRS_Result {
+            _UVRSR_OK = 0,
+            _UVRSR_NOT_IMPLEMENTED = 1,
+            _UVRSR_FAILED = 2,
+        }
+        #[repr(C)]
+        enum _Unwind_VRS_RegClass {
+            _UVRSC_CORE = 0,
+            _UVRSC_VFP = 1,
+            _UVRSC_FPA = 2,
+            _UVRSC_WMMXD = 3,
+            _UVRSC_WMMXC = 4,
+        }
+        #[repr(C)]
+        enum _Unwind_VRS_DataRepresentation {
+            _UVRSD_UINT32 = 0,
+            _UVRSD_VFPX = 1,
+            _UVRSD_FPAX = 2,
+            _UVRSD_UINT64 = 3,
+            _UVRSD_FLOAT = 4,
+            _UVRSD_DOUBLE = 5,
+        }
+
+        type _Unwind_Word = libc::c_uint;
+        extern {
+            fn _Unwind_VRS_Get(ctx: *mut _Unwind_Context,
+                               klass: _Unwind_VRS_RegClass,
+                               word: _Unwind_Word,
+                               repr: _Unwind_VRS_DataRepresentation,
+                               data: *mut libc::c_void)
+                -> _Unwind_VRS_Result;
+        }
+
+        let mut val: _Unwind_Word = 0;
+        let ptr = &mut val as *mut _Unwind_Word;
+        let _ = _Unwind_VRS_Get(ctx, _Unwind_VRS_RegClass::_UVRSC_CORE, 15,
+                                _Unwind_VRS_DataRepresentation::_UVRSD_UINT32,
+                                ptr as *mut libc::c_void);
+        (val & !1) as libc::uintptr_t
+    }
+
+    // This function doesn't exist on Android or ARM/Linux, so make it same
+    // to _Unwind_GetIP
+    #[cfg(any(all(target_os = "android", target_arch = "arm"),
+              all(target_os = "linux", target_arch = "arm")))]
+    pub unsafe fn _Unwind_GetIPInfo(ctx: *mut _Unwind_Context,
+                                    ip_before_insn: *mut libc::c_int)
+        -> libc::uintptr_t
+    {
+        *ip_before_insn = 0;
+        _Unwind_GetIP(ctx)
+    }
+
+    // This function also doesn't exist on Android or ARM/Linux, so make it
+    // a no-op
+    #[cfg(any(target_os = "android",
+              all(target_os = "linux", target_arch = "arm")))]
+    pub unsafe fn _Unwind_FindEnclosingFunction(pc: *mut libc::c_void)
+        -> *mut libc::c_void
+    {
+        pc
+    }
+}
diff --git a/src/libstd/sys/unix/backtrace/tracing/mod.rs b/src/libstd/sys/unix/backtrace/tracing/mod.rs
new file mode 100644
index 00000000000..c9c8e260d2f
--- /dev/null
+++ b/src/libstd/sys/unix/backtrace/tracing/mod.rs
@@ -0,0 +1,18 @@
+// Copyright 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.
+
+pub use self::imp::*;
+
+#[cfg(not(all(target_os = "ios", target_arch = "arm")))]
+#[path = "gcc_s.rs"]
+mod imp;
+#[cfg(all(target_os = "ios", target_arch = "arm"))]
+#[path = "backtrace_fn.rs"]
+mod imp;