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

use backtrace_sys::backtrace_state;

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

pub fn foreach_symbol_fileline<F>(frame: Frame,
                                  mut f: F,
                                  _: &BacktraceContext) -> io::Result<bool>
where F: FnMut(&[u8], u32) -> 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(), !0); FILELINE_SIZE];
    let ret;
    let fileline_count = {
        let state = unsafe { init_state() };
        if state.is_null() {
            return Err(io::Error::new(
                io::ErrorKind::Other,
                "failed to allocate libbacktrace state")
            )
        }
        let mut fileline_win: &mut [FileLine] = &mut fileline_buf;
        let fileline_addr = &mut fileline_win as *mut &mut [FileLine];
        ret = unsafe {
            backtrace_sys::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() {
            return Err(io::Error::new(
                io::ErrorKind::Other,
                "failed to allocate libbacktrace state")
            )
        }
        let mut data: *const libc::c_char = ptr::null();
        let data_addr = &mut data as *mut *const libc::c_char;
        let ret = unsafe {
            backtrace_sys::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)
}

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

type FileLine = (*const libc::c_char, u32);

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 as u32);
            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 crate::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_sys::backtrace_create_state(
        filename,
        0,
        error_cb,
        ptr::null_mut(),
    );
    STATE
}