Rollup merge of rust-lang#38165 - Yamakaky:better-backtrace, r=alexcr…

…ichton

Improve backtrace formating while panicking.

Fixes rust-lang#37783.

Done:

- Fix alignment of file paths for better readability
- `RUST_BACKTRACE=full` prints all the informations (current behaviour)
- `RUST_BACKTRACE=(short|yes)` is the default and does:
  - Skip irrelevant frames at the beginning and the end
  - Remove function address
  - Remove the current directory from the absolute paths
  - Remove `::hfabe6541873` at the end of the symbols
- `RUST_BACKTRACE=(0|no)` disables the backtrace.
- `RUST_BACKTRACE=<everything else>` is equivalent to `short` for
  backward compatibility.
- doc
- More uniform printing across platforms.

Removed, TODO in a new PR:

- Remove path prefix for libraries and libstd

Example of short backtrace:
```rust
fn fail() {
    panic!();
}

fn main() {
    let closure = || fail();
    closure();
}
```
Short:
```
thread 'main' panicked at 'explicit panic', t.rs:2
Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: t::fail
            at ./t.rs:2
   1: t::main::{{closure}}
            at ./t.rs:6
   2: t::main
            at ./t.rs:7
```
Full:
```
thread 'main' panicked at 'This function never returns!', t.rs:2
stack backtrace:
   0:     0x558ddf666478 - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::hec84c9dd8389cc5d
                               at /home/yamakaky/dev/rust/rust/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1:     0x558ddf65d90e - std::sys_common::backtrace::_print::hfa25f8b31f4b4353
                               at /home/yamakaky/dev/rust/rust/src/libstd/sys_common/backtrace.rs:71
   2:     0x558ddf65cb5e - std::sys_common::backtrace::print::h9b711e11ac3ba805
                               at /home/yamakaky/dev/rust/rust/src/libstd/sys_common/backtrace.rs:60
   3:     0x558ddf66796e - std::panicking::default_hook::{{closure}}::h736d216e74748044
                               at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:355
   4:     0x558ddf66743c - std::panicking::default_hook::h16baff397e46ea10
                               at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:371
   5:     0x558ddf6682bc - std::panicking::rust_panic_with_hook::h6d5a9bb4eca42c80
                               at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:559
   6:     0x558ddf64ea93 - std::panicking::begin_panic::h17dc549df2f10b99
                               at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:521
   7:     0x558ddf64ec42 - t::diverges::he6bc43fc925905f5
                               at /tmp/p/t.rs:2
   8:     0x558ddf64ec5a - t::main::h0ffc20356b8a69c0
                               at /tmp/p/t.rs:6
   9:     0x558ddf6687f5 - core::ops::FnOnce::call_once::hce41f19c0db56f93
  10:     0x558ddf667cde - std::panicking::try::do_call::hd4c8c97efb4291df
                               at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:464
  11:     0x558ddf698d77 - __rust_try
  12:     0x558ddf698c57 - __rust_maybe_catch_panic
                               at /home/yamakaky/dev/rust/rust/src/libpanic_unwind/lib.rs:98
  13:     0x558ddf667adb - std::panicking::try::h2c56ed2a59ec1d12
                               at /home/yamakaky/dev/rust/rust/src/libstd/panicking.rs:440
  14:     0x558ddf66cc9a - std::panic::catch_unwind::h390834e0251cc9af
                               at /home/yamakaky/dev/rust/rust/src/libstd/panic.rs:361
  15:     0x558ddf6809ee - std::rt::lang_start::hb73087428e233982
                               at /home/yamakaky/dev/rust/rust/src/libstd/rt.rs:57
  16:     0x558ddf64ec92 - main
  17:     0x7fecb869e290 - __libc_start_main
  18:     0x558ddf64e8b9 - _start
  19:                0x0 - <unknown>
```

src/doc/book/functions.md

@@ -230,6 +230,19 @@ If you want more information, you can get a backtrace by setting the
 ```text
 $ RUST_BACKTRACE=1 ./diverges
 thread 'main' panicked at 'This function never returns!', hello.rs:2
+Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
+stack backtrace:
+  hello::diverges
+        at ./hello.rs:2
+  hello::main
+        at ./hello.rs:6
+```
+
+If you want the complete backtrace and filenames:
+
+```text
+$ RUST_BACKTRACE=full ./diverges
+thread 'main' panicked at 'This function never returns!', hello.rs:2
 stack backtrace:
    1:     0x7f402773a829 - sys::backtrace::write::h0942de78b6c02817K8r
    2:     0x7f402773d7fc - panicking::on_panic::h3f23f9d0b5f4c91bu9w
@@ -262,7 +275,7 @@ note: Run with `RUST_BACKTRACE=1` for a backtrace.
 `RUST_BACKTRACE` also works with Cargo’s `run` command:
 
 ```text
-$ RUST_BACKTRACE=1 cargo run
+$ RUST_BACKTRACE=full cargo run
      Running `target/debug/diverges`
 thread 'main' panicked at 'This function never returns!', hello.rs:2
 stack backtrace:

src/libstd/panicking.rs

@@ -320,7 +320,11 @@ fn default_hook(info: &PanicInfo) {
     let log_backtrace = {
         let panics = update_panic_count(0);
 
-        panics >= 2 || backtrace::log_enabled()
+        if panics >= 2 {
+            Some(backtrace::PrintFormat::Full)
+        } else {
+            backtrace::log_enabled()
+        }
     };
 
     let file = info.location.file;
@@ -347,8 +351,8 @@ fn default_hook(info: &PanicInfo) {
 
             static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
 
-            if log_backtrace {
-                let _ = backtrace::write(err);
+            if let Some(format) = log_backtrace {
+                let _ = backtrace::print(err, format);
             } else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
                 let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=1` for a backtrace.");
             }

src/libstd/sys/redox/backtrace.rs

@@ -10,9 +10,14 @@
 
 use libc;
 use io;
-use sys_common::backtrace::output;
+use sys_common::backtrace::Frame;
+
+pub use sys_common::gnu::libbacktrace::*;
+pub struct BacktraceContext;
 
 #[inline(never)]
-pub fn write(w: &mut io::Write) -> io::Result<()> {
-    output(w, 0, 0 as *mut libc::c_void, None)
+pub fn unwind_backtrace(frames: &mut [Frame])
+    -> io::Result<(usize, BacktraceContext)>
+{
+    Ok((0, BacktraceContext))
 }

src/libstd/sys/unix/backtrace/mod.rs

@@ -83,7 +83,8 @@
 /// to symbols. This is a bit of a hokey implementation as-is, but it works for
 /// all unix platforms we support right now, so it at least gets the job done.
 
-pub use self::tracing::write;
+pub use self::tracing::unwind_backtrace;
+pub use self::printing::{foreach_symbol_fileline, resolve_symname};
 
 // tracing impls:
 mod tracing;
@@ -100,3 +101,5 @@ pub mod gnu {
         Err(io::Error::new(io::ErrorKind::Other, "Not implemented"))
     }
 }
+
+pub struct BacktraceContext;

src/libstd/sys/unix/backtrace/printing/dladdr.rs

@@ -11,10 +11,11 @@
 use io;
 use io::prelude::*;
 use libc;
+use sys_common::backtrace::Frame;
 
-pub fn print(w: &mut Write, idx: isize, addr: *mut libc::c_void,
-             _symaddr: *mut libc::c_void) -> io::Result<()> {
-    use sys_common::backtrace::{output};
+pub fn resolve_symname<F>(frame: Frame, callback: F) -> io::Result<()>
+    where F: FnOnce(Option<&str>) -> io::Result<()>
+{
     use intrinsics;
     use ffi::CStr;
 
@@ -31,11 +32,20 @@ pub fn print(w: &mut Write, idx: isize, addr: *mut libc::c_void,
     }
 
     let mut info: Dl_info = unsafe { intrinsics::init() };
-    if unsafe { dladdr(addr, &mut info) == 0 } {
-        output(w, idx,addr, None)
+    let symname = if unsafe { dladdr(frame.exact_position, &mut info) == 0 } {
+        None
     } else {
-        output(w, idx, addr, Some(unsafe {
-            CStr::from_ptr(info.dli_sname).to_bytes()
-        }))
-    }
+        unsafe {
+            CStr::from_ptr(info.dli_sname).to_str().ok()
+        }
+    };
+    callback(symname)
+}
+
+pub fn foreach_symbol_fileline<F>(_symbol_addr: Frame,
+                                  mut _f: F
+                                  _: &BacktraceContext) -> io::Result<bool>
+    where F: FnMut(&[u8], libc::c_int) -> io::Result<()>
+{
+    Ok(())
 }

src/libstd/sys/unix/backtrace/printing/mod.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-pub use self::imp::print;
+pub use self::imp::{foreach_symbol_fileline, resolve_symname};
 
 #[cfg(any(target_os = "macos", target_os = "ios",
           target_os = "emscripten"))]
@@ -17,5 +17,6 @@ mod imp;
 
 #[cfg(not(any(target_os = "macos", target_os = "ios",
               target_os = "emscripten")))]
-#[path = "gnu.rs"]
-mod imp;
+mod imp {
+    pub use sys_common::gnu::libbacktrace::{foreach_symbol_fileline, resolve_symname};
+}

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

@@ -22,35 +22,26 @@ use io::prelude::*;
 use io;
 use libc;
 use mem;
-use sys::mutex::Mutex;
+use sys::backtrace::BacktraceContext;
+use sys_common::backtrace::Frame;
 
-use super::super::printing::print;
-
-#[inline(never)]
-pub fn write(w: &mut Write) -> io::Result<()> {
-    extern {
-        fn backtrace(buf: *mut *mut libc::c_void,
-                     sz: libc::c_int) -> libc::c_int;
-    }
-
-    // while it doesn't requires lock for work as everything is
-    // local, it still displays much nicer backtraces when a
-    // couple of threads panic simultaneously
-    static LOCK: Mutex = Mutex::new();
-    unsafe {
-        LOCK.lock();
-
-        writeln!(w, "stack backtrace:")?;
-        // 100 lines should be enough
-        const SIZE: usize = 100;
-        let mut buf: [*mut libc::c_void; SIZE] = mem::zeroed();
-        let cnt = backtrace(buf.as_mut_ptr(), SIZE as libc::c_int) as usize;
-
-        // skipping the first one as it is write itself
-        for i in 1..cnt {
-            print(w, i as isize, buf[i], buf[i])?
-        }
-        LOCK.unlock();
+#[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)>
+{
+    const FRAME_LEN = 100;
+    assert!(FRAME_LEN >= frames);
+    let mut raw_frames = [0; FRAME_LEN];
+    let nb_frames = backtrace(frames.as_mut_ptr(),
+                              frames.len() as libc::c_int);
+    for (from, to) in raw_frames[..nb_frames].iter().zip(frames.iter_mut()) {
+        *to = Frame {
+            exact_position: *from,
+            symbol_addr: *from,
+        };
     }
-    Ok(())
+    (nb_frames as usize, BacktraceContext)
 }
+
+extern fn backtrace(buf: *mut *mut libc::c_void, sz: libc::c_int) -> libc::c_int;

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

@@ -8,102 +8,97 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use error::Error;
 use io;
-use io::prelude::*;
 use libc;
-use mem;
-use sys_common::mutex::Mutex;
+use sys::backtrace::BacktraceContext;
+use sys_common::backtrace::Frame;
 
-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>,
-    }
+struct Context<'a> {
+    idx: usize,
+    frames: &'a mut [Frame],
+}
 
-    // 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();
+#[derive(Debug)]
+struct UnwindError(uw::_Unwind_Reason_Code);
 
-        writeln!(w, "stack backtrace:")?;
+impl Error for UnwindError {
+    fn description(&self) -> &'static str {
+        "unexpected return value while unwinding"
+    }
+}
 
-        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
+impl ::fmt::Display for UnwindError {
+    fn fmt(&self, f: &mut ::fmt::Formatter) -> ::fmt::Result {
+        write!(f, "{}: {:?}", self.description(), self.0)
     }
+}
 
-    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 _;
+#[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: 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 {
+        uw::_URC_END_OF_STACK | uw::_URC_FATAL_PHASE1_ERROR => {
+            Ok((cx.idx, BacktraceContext))
         }
-
-        // 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
+        _ => {
+            Err(io::Error::new(io::ErrorKind::Other,
+                               UnwindError(result_unwind)))
         }
+    }
+}
 
-        // Once we hit an error, stop trying to print more frames
-        if cx.last_error.is_some() { return uw::_URC_FAILURE }
+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 _;
+    }
 
-        match print(cx.writer, cx.idx, ip, symaddr) {
-            Ok(()) => {}
-            Err(e) => { cx.last_error = Some(e); }
-        }
+    // 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) }
+    };
 
-        // keep going
-        uw::_URC_NO_REASON
+    if cx.idx < cx.frames.len() {
+        cx.frames[cx.idx] = Frame {
+            symbol_addr: symaddr,
+            exact_position: ip,
+        };
+        cx.idx += 1;
     }
+
+    uw::_URC_NO_REASON
 }