std: Depend on `backtrace` crate from crates.io

This commit removes all in-tree support for generating backtraces in
favor of depending on the `backtrace` crate on crates.io. This resolves
a very longstanding piece of duplication where the standard library has
long contained the ability to generate a backtrace on panics, but the
code was later extracted and duplicated on crates.io with the
`backtrace` crate. Since that fork each implementation has seen various
improvements one way or another, but typically `backtrace`-the-crate has
lagged behind libstd in one way or another.

The goal here is to remove this duplication of a fairly critical piece
of code and ensure that there's only one source of truth for generating
backtraces between the standard library and the crate on crates.io.
Recently I've been working to bring the `backtrace` crate on crates.io
up to speed with the support in the standard library which includes:

* Support for `StackWalkEx` on MSVC to recover inline frames with
  debuginfo.
* Using `libbacktrace` by default on MinGW targets.
* Supporting `libbacktrace` on OSX as an option.
* Ensuring all the requisite support in `backtrace`-the-crate compiles
  with `#![no_std]`.
* Updating the `libbacktrace` implementation in `backtrace`-the-crate to
  initialize the global state with the correct filename where necessary.

After reviewing the code in libstd the `backtrace` crate should be at
exact feature parity with libstd today. The backtraces generated should
have the same symbols and same number of frames in general, and there's
not known divergence from libstd currently.

Note that one major difference between libstd's backtrace support and
the `backtrace` crate is that on OSX the crates.io crate enables the
`coresymbolication` feature by default. This feature, however, uses
private internal APIs that aren't published for OSX. While they provide
more accurate backtraces this isn't appropriate for libstd distributed
as a binary, so libstd's dependency on the `backtrace` crate explicitly
disables this feature and forces OSX to use `libbacktrace` as a
symbolication strategy.

The long-term goal of this refactoring is to eventually move us towards
a world where we can drop `libbacktrace` entirely and simply use Gimli
and the surrounding crates for backtrace support. That's still aways off
but hopefully will much more easily enabled by having the source of
truth for backtraces live in crates.io!

Procedurally if we go forward with this I'd like to transfer the
`backtrace-rs` crate to the rust-lang GitHub organization as well, but I
figured I'd hold off on that until we get closer to merging.

7 files changed, 0 insertions, 325 deletions

diff --git a/src/libstd/sys/unix/backtrace/mod.rs b/src/libstd/sys/unix/backtrace/mod.rs
deleted file mode 100644
index 0887e5a4df9..00000000000
--- a/src/libstd/sys/unix/backtrace/mod.rs
+++ /dev/null
@@ -1,110 +0,0 @@
-/// Backtrace support built on libgcc with some extra OS-specific support
-///
-/// Some methods of getting a backtrace:
-///
-/// * The backtrace() functions on unix. It turns out this doesn't work very
-///   well for green threads on macOS, and the address to symbol portion of it
-///   suffers problems that are described below.
-///
-/// * Using libunwind. This is more difficult than it sounds because libunwind
-///   isn't installed everywhere by default. It's also a bit of a hefty library,
-///   so possibly not the best option. When testing, libunwind was excellent at
-///   getting both accurate backtraces and accurate symbols across platforms.
-///   This route was not chosen in favor of the next option, however.
-///
-/// * We're already using libgcc_s for exceptions in rust (triggering thread
-///   unwinding and running destructors on the stack), and it turns out that it
-///   conveniently comes with a function that also gives us a backtrace. All of
-///   these functions look like _Unwind_*, but it's not quite the full
-///   repertoire of the libunwind API. Due to it already being in use, this was
-///   the chosen route of getting a backtrace.
-///
-/// After choosing libgcc_s for backtraces, the sad part is that it will only
-/// give us a stack trace of instruction pointers. Thankfully these instruction
-/// pointers are accurate (they work for green and native threads), but it's
-/// then up to us again to figure out how to translate these addresses to
-/// symbols. As with before, we have a few options. Before, that, a little bit
-/// of an interlude about symbols. This is my very limited knowledge about
-/// symbol tables, and this information is likely slightly wrong, but the
-/// general idea should be correct.
-///
-/// When talking about symbols, it's helpful to know a few things about where
-/// symbols are located. Some symbols are located in the dynamic symbol table
-/// of the executable which in theory means that they're available for dynamic
-/// linking and lookup. Other symbols end up only in the local symbol table of
-/// the file. This loosely corresponds to pub and priv functions in Rust.
-///
-/// Armed with this knowledge, we know that our solution for address to symbol
-/// translation will need to consult both the local and dynamic symbol tables.
-/// With that in mind, here's our options of translating an address to
-/// a symbol.
-///
-/// * Use dladdr(). The original backtrace()-based idea actually uses dladdr()
-///   behind the scenes to translate, and this is why backtrace() was not used.
-///   Conveniently, this method works fantastically on macOS. It appears dladdr()
-///   uses magic to consult the local symbol table, or we're putting everything
-///   in the dynamic symbol table anyway. Regardless, for macOS, this is the
-///   method used for translation. It's provided by the system and easy to do.o
-///
-///   Sadly, all other systems have a dladdr() implementation that does not
-///   consult the local symbol table. This means that most functions are blank
-///   because they don't have symbols. This means that we need another solution.
-///
-/// * Use unw_get_proc_name(). This is part of the libunwind api (not the
-///   libgcc_s version of the libunwind api), but involves taking a dependency
-///   to libunwind. We may pursue this route in the future if we bundle
-///   libunwind, but libunwind was unwieldy enough that it was not chosen at
-///   this time to provide this functionality.
-///
-/// * Shell out to a utility like `readelf`. Crazy though it may sound, it's a
-///   semi-reasonable solution. The stdlib already knows how to spawn processes,
-///   so in theory it could invoke readelf, parse the output, and consult the
-///   local/dynamic symbol tables from there. This ended up not getting chosen
-///   due to the craziness of the idea plus the advent of the next option.
-///
-/// * Use `libbacktrace`. It turns out that this is a small library bundled in
-///   the gcc repository which provides backtrace and symbol translation
-///   functionality. All we really need from it is the backtrace functionality,
-///   and we only really need this on everything that's not macOS, so this is the
-///   chosen route for now.
-///
-/// In summary, the current situation uses libgcc_s to get a trace of stack
-/// pointers, and we use dladdr() or libbacktrace to translate these addresses
-/// 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::unwind_backtrace;
-pub use self::printing::{foreach_symbol_fileline, resolve_symname};
-
-// tracing impls:
-mod tracing;
-// symbol resolvers:
-mod printing;
-
-#[cfg(not(target_os = "emscripten"))]
-pub mod gnu {
-    use crate::io;
-    use crate::fs;
-
-    use libc::c_char;
-
-    #[cfg(not(any(target_os = "macos", target_os = "ios")))]
-    pub fn get_executable_filename() -> io::Result<(Vec<c_char>, fs::File)> {
-        Err(io::Error::new(io::ErrorKind::Other, "Not implemented"))
-    }
-
-    #[cfg(any(target_os = "macos", target_os = "ios"))]
-    pub fn get_executable_filename() -> io::Result<(Vec<c_char>, fs::File)> {
-        use crate::env;
-        use crate::os::unix::ffi::OsStrExt;
-
-        let filename = env::current_exe()?;
-        let file = fs::File::open(&filename)?;
-        let mut filename_cstr: Vec<_> = filename.as_os_str().as_bytes().iter()
-            .map(|&x| x as c_char).collect();
-        filename_cstr.push(0); // Null terminate
-        Ok((filename_cstr, file))
-    }
-}
-
-pub struct BacktraceContext;
diff --git a/src/libstd/sys/unix/backtrace/printing/dladdr.rs b/src/libstd/sys/unix/backtrace/printing/dladdr.rs
deleted file mode 100644
index cf3bda640e9..00000000000
--- a/src/libstd/sys/unix/backtrace/printing/dladdr.rs
+++ /dev/null
@@ -1,34 +0,0 @@
-use crate::io;
-use crate::intrinsics;
-use crate::ffi::CStr;
-use crate::sys::backtrace::BacktraceContext;
-use crate::sys_common::backtrace::Frame;
-
-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 as *mut _, &mut info) == 0 ||
-                         info.dli_sname.is_null() {
-            None
-        } else {
-            CStr::from_ptr(info.dli_sname).to_str().ok()
-        };
-        callback(symname)
-    }
-}
-
-#[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;
-}
diff --git a/src/libstd/sys/unix/backtrace/printing/mod.rs b/src/libstd/sys/unix/backtrace/printing/mod.rs
deleted file mode 100644
index d090caede43..00000000000
--- a/src/libstd/sys/unix/backtrace/printing/mod.rs
+++ /dev/null
@@ -1,33 +0,0 @@
-mod dladdr;
-
-use crate::sys::backtrace::BacktraceContext;
-use crate::sys_common::backtrace::Frame;
-use crate::io;
-
-#[cfg(target_os = "emscripten")]
-pub use self::dladdr::resolve_symname;
-
-#[cfg(target_os = "emscripten")]
-pub fn foreach_symbol_fileline<F>(_: Frame, _: F, _: &BacktraceContext) -> io::Result<bool>
-where
-    F: FnMut(&[u8], u32) -> io::Result<()>
-{
-    Ok(false)
-}
-
-#[cfg(not(target_os = "emscripten"))]
-pub use crate::sys_common::gnu::libbacktrace::foreach_symbol_fileline;
-
-#[cfg(not(target_os = "emscripten"))]
-pub fn resolve_symname<F>(frame: Frame, callback: F, bc: &BacktraceContext) -> io::Result<()>
-where
-    F: FnOnce(Option<&str>) -> io::Result<()>
-{
-    crate::sys_common::gnu::libbacktrace::resolve_symname(frame, |symname| {
-        if symname.is_some() {
-            callback(symname)
-        } else {
-            dladdr::resolve_symname(frame, callback, bc)
-        }
-    }, bc)
-}
diff --git a/src/libstd/sys/unix/backtrace/tracing/backtrace_fn.rs b/src/libstd/sys/unix/backtrace/tracing/backtrace_fn.rs
deleted file mode 100644
index a628d107ad6..00000000000
--- a/src/libstd/sys/unix/backtrace/tracing/backtrace_fn.rs
+++ /dev/null
@@ -1,39 +0,0 @@
-/// As always - iOS on arm uses SjLj exceptions and
-/// _Unwind_Backtrace is even not available there. Still,
-/// backtraces could be extracted using a backtrace function,
-/// which thanks god is public
-///
-/// As mentioned in a huge comment block in `super::super`, backtrace
-/// doesn't play well with green threads, so while it is extremely nice and
-/// simple to use it should be used only on iOS devices as the only viable
-/// option.
-
-use crate::io;
-use crate::ptr;
-use crate::sys::backtrace::BacktraceContext;
-use crate::sys_common::backtrace::Frame;
-
-#[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 = [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 as *mut u8,
-            symbol_addr: *from as *mut u8,
-            inline_context: 0,
-        };
-    }
-    Ok((nb_frames as usize, BacktraceContext))
-}
-
-extern {
-    fn backtrace(buf: *mut *mut libc::c_void, sz: libc::c_int) -> libc::c_int;
-}
diff --git a/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs b/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs
deleted file mode 100644
index e6379132baf..00000000000
--- a/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs
+++ /dev/null
@@ -1,99 +0,0 @@
-use crate::error::Error;
-use crate::fmt;
-use crate::io;
-use crate::sys::backtrace::BacktraceContext;
-use crate::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<'_>) };
-    if cx.idx >= cx.frames.len() {
-        return uw::_URC_NORMAL_STOP;
-    }
-
-    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) }
-    };
-
-    cx.frames[cx.idx] = Frame {
-        symbol_addr: symaddr as *mut u8,
-        exact_position: ip as *mut u8,
-        inline_context: 0,
-    };
-    cx.idx += 1;
-
-    uw::_URC_NO_REASON
-}
diff --git a/src/libstd/sys/unix/backtrace/tracing/mod.rs b/src/libstd/sys/unix/backtrace/tracing/mod.rs
deleted file mode 100644
index 11863e64545..00000000000
--- a/src/libstd/sys/unix/backtrace/tracing/mod.rs
+++ /dev/null
@@ -1,8 +0,0 @@
-pub use self::imp::*;
-
-#[cfg(not(all(target_os = "ios", target_arch = "arm")))]
-#[path = "gcc_s.rs"]
-mod imp;
-#[cfg(all(target_os = "ios", target_arch = "arm"))]
-#[path = "backtrace_fn.rs"]
-mod imp;
diff --git a/src/libstd/sys/unix/mod.rs b/src/libstd/sys/unix/mod.rs
index c2b264ff8de..821623db272 100644
--- a/src/libstd/sys/unix/mod.rs
+++ b/src/libstd/sys/unix/mod.rs
@@ -27,8 +27,6 @@ pub mod weak;
 pub mod alloc;
 pub mod args;
 pub mod android;
-#[cfg(feature = "backtrace")]
-pub mod backtrace;
 pub mod cmath;
 pub mod condvar;
 pub mod env;