src/libstd/sys/unix/backtrace/tracing/gcc_s.rs

   1 // Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use error::Error;
  12 use io;
  13 use libc;
  14 use sys::backtrace::BacktraceContext;
  15 use sys_common::backtrace::Frame;
  16
  17 use unwind as uw;
  18
  19 struct Context<'a> {
  20     idx: usize,
  21     frames: &'a mut [Frame],
  22 }
  23
  24 #[derive(Debug)]
  25 struct UnwindError(uw::_Unwind_Reason_Code);
  26
  27 impl Error for UnwindError {
  28     fn description(&self) -> &'static str {
  29         "unexpected return value while unwinding"
  30     }
  31 }
  32
  33 impl ::fmt::Display for UnwindError {
  34     fn fmt(&self, f: &mut ::fmt::Formatter) -> ::fmt::Result {
  35         write!(f, "{}: {:?}", self.description(), self.0)
  36     }
  37 }
  38
  39 #[inline(never)] // if we know this is a function call, we can skip it when
  40                  // tracing
  41 pub fn unwind_backtrace(frames: &mut [Frame])
  42     -> io::Result<(usize, BacktraceContext)>
  43 {
  44     let mut cx = Context {
  45         idx: 0,
  46         frames,
  47     };
  48     let result_unwind = unsafe {
  49         uw::_Unwind_Backtrace(trace_fn,
  50                               &mut cx as *mut Context
  51                               as *mut libc::c_void)
  52     };
  53     // See libunwind:src/unwind/Backtrace.c for the return values.
  54     // No, there is no doc.
  55     match result_unwind {
  56         // These return codes seem to be benign and need to be ignored for backtraces
  57         // to show up properly on all tested platforms.
  58         uw::_URC_END_OF_STACK | uw::_URC_FATAL_PHASE1_ERROR | uw::_URC_FAILURE => {
  59             Ok((cx.idx, BacktraceContext))
  60         }
  61         _ => {
  62             Err(io::Error::new(io::ErrorKind::Other,
  63                                UnwindError(result_unwind)))
  64         }
  65     }
  66 }
  67
  68 extern fn trace_fn(ctx: *mut uw::_Unwind_Context,
  69                    arg: *mut libc::c_void) -> uw::_Unwind_Reason_Code {
  70     let cx = unsafe { &mut *(arg as *mut Context) };
  71     let mut ip_before_insn = 0;
  72     let mut ip = unsafe {
  73         uw::_Unwind_GetIPInfo(ctx, &mut ip_before_insn) as *mut libc::c_void
  74     };
  75     if !ip.is_null() && ip_before_insn == 0 {
  76         // this is a non-signaling frame, so `ip` refers to the address
  77         // after the calling instruction. account for that.
  78         ip = (ip as usize - 1) as *mut _;
  79     }
  80
  81     // dladdr() on osx gets whiny when we use FindEnclosingFunction, and
  82     // it appears to work fine without it, so we only use
  83     // FindEnclosingFunction on non-osx platforms. In doing so, we get a
  84     // slightly more accurate stack trace in the process.
  85     //
  86     // This is often because panic involves the last instruction of a
  87     // function being "call std::rt::begin_unwind", with no ret
  88     // instructions after it. This means that the return instruction
  89     // pointer points *outside* of the calling function, and by
  90     // unwinding it we go back to the original function.
  91     let symaddr = if cfg!(target_os = "macos") || cfg!(target_os = "ios") {
  92         ip
  93     } else {
  94         unsafe { uw::_Unwind_FindEnclosingFunction(ip) }
  95     };
  96
  97     if cx.idx < cx.frames.len() {
  98         cx.frames[cx.idx] = Frame {
  99             symbol_addr: symaddr as *mut u8,
 100             exact_position: ip as *mut u8,
 101             inline_context: 0,
 102         };
 103         cx.idx += 1;
 104     }
 105
 106     uw::_URC_NO_REASON
 107 }