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// Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use io;
use io::prelude::*;
use libc;
use mem;
use sys_common::mutex::Mutex;
use super::super::printing::print;
use unwind as uw;
#[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: Mutex = Mutex::new();
unsafe {
LOCK.lock();
writeln!(w, "stack backtrace:")?;
let mut cx = Context { writer: w, last_error: None, idx: 0 };
let ret = match {
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(()),
};
LOCK.unlock();
return ret
}
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
}
}
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