0: func_d
             at $DIR/backtrace-std.rs:18
   1: func_c
             at $DIR/backtrace-std.rs:17
   2: func_b
             at $DIR/backtrace-std.rs:11
   3: func_a
             at $DIR/backtrace-std.rs:10
   4: main
             at $DIR/backtrace-std.rs:21
   5: <fn() as std::ops::FnOnce<()>>::call_once - shim(fn())
             at RUSTLIB/core/src/ops/function.rs:LL
   6: std::sys_common::backtrace::__rust_begin_short_backtrace
             at RUSTLIB/std/src/sys_common/backtrace.rs:LL
   7: std::rt::lang_start::{closure#0}
             at RUSTLIB/std/src/rt.rs:LL
   8: std::ops::function::impls::call_once
             at RUSTLIB/core/src/ops/function.rs:LL
   9: std::panicking::r#try::do_call
             at RUSTLIB/std/src/panicking.rs:LL
  10: std::panicking::r#try
             at RUSTLIB/std/src/panicking.rs:LL
  11: std::panic::catch_unwind
             at RUSTLIB/std/src/panic.rs:LL
  12: std::rt::lang_start_internal
             at RUSTLIB/std/src/rt.rs:LL
  13: std::rt::lang_start
             at RUSTLIB/std/src/rt.rs:LL