Improve backtrace formating while panicking.

- `RUST_BACKTRACE=full` prints all the informations (old behaviour)
- `RUST_BACKTRACE=(0|no)` disables the backtrace.
- `RUST_BACKTRACE=<everything else>` (including `1`) shows a simplified
  backtrace, without the function addresses and with cleaned filenames
  and symbols. Also removes some unneded frames at the beginning and the
  end.

Fixes #37783.

PR is #38165.

2 files changed, 408 insertions, 189 deletions

diff --git a/src/libstd/sys_common/backtrace.rs b/src/libstd/sys_common/backtrace.rs
index a8540fed928..a19f7954e8f 100644
--- a/src/libstd/sys_common/backtrace.rs
+++ b/src/libstd/sys_common/backtrace.rs
@@ -10,14 +10,25 @@
 
 #![cfg_attr(target_os = "nacl", allow(dead_code))]
 
+/// Common code for printing the backtrace in the same way across the different
+/// supported platforms.
+
 use env;
 use io::prelude::*;
 use io;
 use libc;
 use str;
 use sync::atomic::{self, Ordering};
+use path::Path;
+use sys::mutex::Mutex;
+use ptr;
 
-pub use sys::backtrace::write;
+pub use sys::backtrace::{
+    unwind_backtrace,
+    resolve_symname,
+    foreach_symbol_fileline,
+    BacktraceContext
+};
 
 #[cfg(target_pointer_width = "64")]
 pub const HEX_WIDTH: usize = 18;
@@ -25,45 +36,217 @@ pub const HEX_WIDTH: usize = 18;
 #[cfg(target_pointer_width = "32")]
 pub const HEX_WIDTH: usize = 10;
 
+/// Represents an item in the backtrace list. See `unwind_backtrace` for how
+/// it is created.
+#[derive(Debug, Copy, Clone)]
+pub struct Frame {
+    /// Exact address of the call that failed.
+    pub exact_position: *const libc::c_void,
+    /// Address of the enclosing function.
+    pub symbol_addr: *const libc::c_void,
+}
+
+/// Max number of frames to print.
+const MAX_NB_FRAMES: usize = 100;
+
+/// Prints the current backtrace.
+pub fn print(w: &mut Write, format: PrintFormat) -> io::Result<()> {
+    static LOCK: Mutex = Mutex::new();
+
+    // Use a lock to prevent mixed output in multithreading context.
+    // Some platforms also requires it, like `SymFromAddr` on Windows.
+    unsafe {
+        LOCK.lock();
+        let res = _print(w, format);
+        LOCK.unlock();
+        res
+    }
+}
+
+fn _print(w: &mut Write, format: PrintFormat) -> io::Result<()> {
+    let mut frames = [Frame {
+        exact_position: ptr::null(),
+        symbol_addr: ptr::null(),
+    }; MAX_NB_FRAMES];
+    let (nb_frames, context) = unwind_backtrace(&mut frames)?;
+    let (skipped_before, skipped_after) =
+        filter_frames(&frames[..nb_frames], format, &context);
+    if format == PrintFormat::Short {
+        writeln!(w, "note: Some details are omitted, \
+                     run with `RUST_BACKTRACE=full` for a verbose backtrace.")?;
+    }
+    writeln!(w, "stack backtrace:")?;
+
+    let filtered_frames = &frames[..nb_frames - skipped_after];
+    for (index, frame) in filtered_frames.iter().skip(skipped_before).enumerate() {
+        resolve_symname(*frame, |symname| {
+            output(w, index, *frame, symname, format)
+        }, &context)?;
+        let has_more_filenames = foreach_symbol_fileline(*frame, |file, line| {
+            output_fileline(w, file, line, format)
+        }, &context)?;
+        if has_more_filenames {
+            w.write_all(b" <... and possibly more>")?;
+        }
+    }
+
+    Ok(())
+}
+
+fn filter_frames(frames: &[Frame],
+                 format: PrintFormat,
+                 context: &BacktraceContext) -> (usize, usize)
+{
+    if format == PrintFormat::Full {
+        return (0, 0);
+    }
+
+    let mut skipped_before = 0;
+    for (i, frame) in frames.iter().enumerate() {
+        skipped_before = i;
+        let mut skip = false;
+
+        let _ = resolve_symname(*frame, |symname| {
+            if let Some(mangled_symbol_name) = symname {
+                let magics_begin = [
+                    "_ZN3std3sys3imp9backtrace",
+                    "_ZN3std10sys_common9backtrace",
+                    "_ZN3std9panicking",
+                    "_ZN4core9panicking",
+                    "rust_begin_unwind",
+                    "_ZN4core6result13unwrap_failed",
+                ];
+                if !magics_begin.iter().any(|s| mangled_symbol_name.starts_with(s)) {
+                    skip = true;
+                }
+            }
+            Ok(())
+        }, context);
+
+        if skip {
+            break;
+        }
+    }
+
+    let mut skipped_after = 0;
+    for (i, frame) in frames.iter().rev().enumerate() {
+        let _ = resolve_symname(*frame, |symname| {
+            if let Some(mangled_symbol_name) = symname {
+                let magics_end = [
+                    "_ZN3std9panicking3try7do_call",
+                    "__rust_maybe_catch_panic",
+                    "__libc_start_main",
+                    "__rust_try",
+                    "_start",
+                ];
+                if magics_end.iter().any(|s| mangled_symbol_name.starts_with(s)) {
+                    skipped_after = i + 1;
+                }
+            }
+            Ok(())
+        }, context);
+    }
+
+    (skipped_before, skipped_after)
+}
+
+/// Controls how the backtrace should be formated.
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum PrintFormat {
+    /// Show all the frames with absolute path for files.
+    Full = 2,
+    /// Show only relevant data from the backtrace.
+    Short = 3,
+}
+
 // For now logging is turned off by default, and this function checks to see
 // whether the magical environment variable is present to see if it's turned on.
-pub fn log_enabled() -> bool {
+pub fn log_enabled() -> Option<PrintFormat> {
     static ENABLED: atomic::AtomicIsize = atomic::AtomicIsize::new(0);
     match ENABLED.load(Ordering::SeqCst) {
-        1 => return false,
-        2 => return true,
-        _ => {}
+        0 => {},
+        1 => return None,
+        2 => return Some(PrintFormat::Full),
+        3 => return Some(PrintFormat::Short),
+        _ => unreachable!(),
     }
 
     let val = match env::var_os("RUST_BACKTRACE") {
-        Some(x) => if &x == "0" { 1 } else { 2 },
-        None => 1,
+        Some(x) => if &x == "0" {
+            None
+        } else if &x == "full" {
+            Some(PrintFormat::Full)
+        } else {
+            Some(PrintFormat::Short)
+        },
+        None => None,
     };
-    ENABLED.store(val, Ordering::SeqCst);
-    val == 2
+    ENABLED.store(match val {
+        Some(v) => v as isize,
+        None => 1,
+    }, Ordering::SeqCst);
+    val
 }
 
-// These output functions should now be used everywhere to ensure consistency.
-pub fn output(w: &mut Write, idx: isize, addr: *mut libc::c_void,
-              s: Option<&[u8]>) -> io::Result<()> {
-    write!(w, "  {:2}: {:2$?} - ", idx, addr, HEX_WIDTH)?;
-    match s.and_then(|s| str::from_utf8(s).ok()) {
-        Some(string) => demangle(w, string)?,
-        None => write!(w, "<unknown>")?,
+/// Print the symbol of the backtrace frame.
+///
+/// These output functions should now be used everywhere to ensure consistency.
+/// You may want to also use `output_fileline`.
+fn output(w: &mut Write, idx: usize, frame: Frame,
+              s: Option<&str>, format: PrintFormat) -> io::Result<()> {
+    // Remove the `17: 0x0 - <unknown>` line.
+    if format == PrintFormat::Short && frame.exact_position == ptr::null() {
+        return Ok(());
+    }
+    match format {
+        PrintFormat::Full => write!(w,
+                                    "  {:2}: {:2$?} - ",
+                                    idx,
+                                    frame.exact_position,
+                                    HEX_WIDTH)?,
+        PrintFormat::Short => write!(w, "  {:2}: ", idx)?,
     }
-    w.write_all(&['\n' as u8])
+    match s {
+        Some(string) => demangle(w, string, format)?,
+        None => w.write_all(b"<unknown>")?,
+    }
+    w.write_all(b"\n")
 }
 
+/// Print the filename and line number of the backtrace frame.
+///
+/// See also `output`.
 #[allow(dead_code)]
-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>");
+fn output_fileline(w: &mut Write, file: &[u8], line: libc::c_int,
+                       format: PrintFormat) -> io::Result<()> {
     // prior line: "  ##: {:2$} - func"
-    write!(w, "      {:3$}at {}:{}", "", file, line, HEX_WIDTH)?;
-    if more {
-        write!(w, " <... and possibly more>")?;
+    w.write_all(b"")?;
+    match format {
+        PrintFormat::Full => write!(w,
+                                    "           {:1$}",
+                                    "",
+                                    HEX_WIDTH)?,
+        PrintFormat::Short => write!(w, "           ")?,
     }
-    w.write_all(&['\n' as u8])
+
+    let file = str::from_utf8(file).unwrap_or("<unknown>");
+    let file_path = Path::new(file);
+    let mut already_printed = false;
+    if format == PrintFormat::Short && file_path.is_absolute() {
+        if let Ok(cwd) = env::current_dir() {
+            if let Ok(stripped) = file_path.strip_prefix(&cwd) {
+                if let Some(s) = stripped.to_str() {
+                    write!(w, "  at ./{}:{}", s, line)?;
+                    already_printed = true;
+                }
+            }
+        }
+    }
+    if !already_printed {
+        write!(w, "  at {}:{}", file, line)?;
+    }
+
+    w.write_all(b"\n")
 }
 
 
@@ -84,7 +267,7 @@ pub fn output_fileline(w: &mut Write, file: &[u8], line: libc::c_int,
 // Note that this demangler isn't quite as fancy as it could be. We have lots
 // of other information in our symbols like hashes, version, type information,
 // etc. Additionally, this doesn't handle glue symbols at all.
-pub fn demangle(writer: &mut Write, s: &str) -> io::Result<()> {
+pub fn demangle(writer: &mut Write, s: &str, format: PrintFormat) -> io::Result<()> {
     // First validate the symbol. If it doesn't look like anything we're
     // expecting, we just print it literally. Note that we must handle non-rust
     // symbols because we could have any function in the backtrace.
@@ -123,6 +306,22 @@ pub fn demangle(writer: &mut Write, s: &str) -> io::Result<()> {
     if !valid {
         writer.write_all(s.as_bytes())?;
     } else {
+        // remove the `::hfc2edb670e5eda97` part at the end of the symbol.
+        if format == PrintFormat::Short {
+            // The symbol in still mangled.
+            let mut split = inner.rsplitn(2, "17h");
+            match (split.next(), split.next()) {
+                (Some(addr), rest) => {
+                    if addr.len() == 16 &&
+                       addr.chars().all(|c| c.is_digit(16))
+                    {
+                        inner = rest.unwrap_or("");
+                    }
+                }
+                _ => (),
+            }
+        }
+
         let mut first = true;
         while !inner.is_empty() {
             if !first {
@@ -208,7 +407,9 @@ mod tests {
     use sys_common;
     macro_rules! t { ($a:expr, $b:expr) => ({
         let mut m = Vec::new();
-        sys_common::backtrace::demangle(&mut m, $a).unwrap();
+        sys_common::backtrace::demangle(&mut m,
+                                        $a,
+                                        super::PrintFormat::Full).unwrap();
         assert_eq!(String::from_utf8(m).unwrap(), $b);
     }) }
 
diff --git a/src/libstd/sys_common/gnu/libbacktrace.rs b/src/libstd/sys_common/gnu/libbacktrace.rs
index 0bdbeddb112..1ea5cca44c7 100644
--- a/src/libstd/sys_common/gnu/libbacktrace.rs
+++ b/src/libstd/sys_common/gnu/libbacktrace.rs
@@ -8,186 +8,204 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use io;
-use io::prelude::*;
 use libc;
-use sys_common::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 ffi::CStr;
-    use mem;
-    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 {}
-
-    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
-    }
-
-    ////////////////////////////////////////////////////////////////////////
-    // 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() {
-        output(w, idx, addr, None)?;
-    } else {
-        output(w, idx, addr, Some(unsafe { CStr::from_ptr(data).to_bytes() }))?;
-    }
 
+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 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, addr as libc::uintptr_t,
-                             pcinfo_cb, error_cb,
+            backtrace_pcinfo(state,
+                             frame.exact_position as libc::uintptr_t,
+                             pcinfo_cb,
+                             error_cb,
                              fileline_addr as *mut libc::c_void)
         };
-        fileline_count = FILELINE_SIZE - fileline_win.len();
-    }
+        FILELINE_SIZE - fileline_win.len()
+    };
     if ret == 0 {
-        for (i, &(file, line)) in fileline_buf[..fileline_count].iter().enumerate() {
+        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() };
-            output_fileline(w, file, line, i == FILELINE_SIZE - 1)?;
+            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 {}
+#[link(name = "backtrace", kind = "static")]
+#[cfg(all(not(test), not(cargobuild)))]
+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..]); }
         }
     }
 
-    Ok(())
+    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
 }