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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 error::Error;
use io;
use libc;
use sys::backtrace::BacktraceContext;
use sys_common::backtrace::Frame;
use unwind as uw;
struct Context<'a> {
idx: usize,
frames: &'a mut [Frame],
}
#[derive(Debug)]
struct UnwindError(uw::_Unwind_Reason_Code);
impl Error for UnwindError {
fn description(&self) -> &'static str {
"unexpected return value while unwinding"
}
}
impl ::fmt::Display for UnwindError {
fn fmt(&self, f: &mut ::fmt::Formatter) -> ::fmt::Result {
write!(f, "{}: {:?}", self.description(), self.0)
}
}
#[inline(never)] // if we know this is a function call, we can skip it when
// tracing
pub fn unwind_backtrace(frames: &mut [Frame])
-> io::Result<(usize, BacktraceContext)>
{
let mut cx = Context {
idx: 0,
frames,
};
let result_unwind = unsafe {
uw::_Unwind_Backtrace(trace_fn,
&mut cx as *mut Context
as *mut libc::c_void)
};
// See libunwind:src/unwind/Backtrace.c for the return values.
// No, there is no doc.
match result_unwind {
// These return codes seem to be benign and need to be ignored for backtraces
// to show up properly on all tested platforms.
uw::_URC_END_OF_STACK | uw::_URC_FATAL_PHASE1_ERROR | uw::_URC_FAILURE => {
Ok((cx.idx, BacktraceContext))
}
_ => {
Err(io::Error::new(io::ErrorKind::Other,
UnwindError(result_unwind)))
}
}
}
extern fn trace_fn(ctx: *mut uw::_Unwind_Context,
arg: *mut libc::c_void) -> uw::_Unwind_Reason_Code {
let cx = 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) }
};
if cx.idx < cx.frames.len() {
cx.frames[cx.idx] = Frame {
symbol_addr: symaddr as *mut u8,
exact_position: ip as *mut u8,
};
cx.idx += 1;
}
uw::_URC_NO_REASON
}
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