Auto merge of #38165 - Yamakaky:better-backtrace, r=alexcrichton

Improve backtrace formating while panicking.

Fixes #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>
```

Author: bors

src/doc/book/src/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

@@ -9,33 +9,45 @@
 // except according to those terms.
 
 use io;
-use io::prelude::*;
+use intrinsics;
+use ffi::CStr;
 use libc;
+use sys::backtrace::BacktraceContext;
+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};
-    use intrinsics;
-    use ffi::CStr;
-
-    #[repr(C)]
-    struct Dl_info {
-        dli_fname: *const libc::c_char,
-        dli_fbase: *mut libc::c_void,
-        dli_sname: *const libc::c_char,
-        dli_saddr: *mut libc::c_void,
-    }
-    extern {
-        fn dladdr(addr: *const libc::c_void,
-                  info: *mut Dl_info) -> libc::c_int;
+pub fn resolve_symname<F>(frame: Frame,
+                          callback: F,
+                          _: &BacktraceContext) -> io::Result<()>
+    where F: FnOnce(Option<&str>) -> io::Result<()>
+{
+    unsafe {
+        let mut info: Dl_info = intrinsics::init();
+        let symname = if dladdr(frame.exact_position, &mut info) == 0 {
+            None
+        } else {
+            CStr::from_ptr(info.dli_sname).to_str().ok()
+        };
+        callback(symname)
     }
+}
 
-    let mut info: Dl_info = unsafe { intrinsics::init() };
-    if unsafe { dladdr(addr, &mut info) == 0 } {
-        output(w, idx,addr, None)
-    } else {
-        output(w, idx, addr, Some(unsafe {
-            CStr::from_ptr(info.dli_sname).to_bytes()
-        }))
-    }
+pub fn foreach_symbol_fileline<F>(_symbol_addr: Frame,
+                                  _f: F,
+                                  _: &BacktraceContext) -> io::Result<bool>
+    where F: FnMut(&[u8], libc::c_int) -> io::Result<()>
+{
+    Ok(false)
+}
+
+#[repr(C)]
+struct Dl_info {
+    dli_fname: *const libc::c_char,
+    dli_fbase: *mut libc::c_void,
+    dli_sname: *const libc::c_char,
+    dli_saddr: *mut libc::c_void,
+}
+
+extern {
+    fn dladdr(addr: *const libc::c_void,
+              info: *mut Dl_info) -> libc::c_int;
 }

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

@@ -18,39 +18,32 @@
 /// simple to use it should be used only on iOS devices as the only viable
 /// option.
 
-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;
+#[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: usize = 100;
+    assert!(FRAME_LEN >= frames.len());
+    let mut raw_frames = [::std::ptr::null_mut(); FRAME_LEN];
+    let nb_frames = unsafe {
+        backtrace(raw_frames.as_mut_ptr(), raw_frames.len() as libc::c_int)
+    } as usize;
+    for (from, to) in raw_frames.iter().zip(frames.iter_mut()).take(nb_frames) {
+        *to = Frame {
+            exact_position: *from,
+            symbol_addr: *from,
+        };
     }
+    Ok((nb_frames as usize, BacktraceContext))
+}
 
-    // 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();
-    }
-    Ok(())
+extern {
+    fn backtrace(buf: *mut *mut libc::c_void, sz: libc::c_int) -> libc::c_int;
 }