1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
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
        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
    }
}