Fix demo on nightly

Also, inline asm no longer works (segmentation fault).

unwind/Cargo.toml

@@ -18,3 +18,4 @@ env_logger = "0.6"
 
 [features]
 nightly = []
+asm = ["nightly"]

unwind/build.rs

@@ -2,7 +2,7 @@ extern crate gcc;
 use std::env;
 
 fn main() {
-    match env::var("CARGO_FEATURE_NIGHTLY") {
+    match env::var("CARGO_FEATURE_ASM") {
         Err(env::VarError::NotPresent) => {
             gcc::Build::new()
                        .file("src/unwind_helper.c")

unwind/src/glue.rs

@@ -4,13 +4,13 @@ use registers::Registers;
 
 #[allow(improper_ctypes)] // trampoline just forwards the ptr
 extern "C" {
-    #[cfg(not(feature = "nightly"))]
+    #[cfg(not(feature = "asm"))]
     pub fn unwind_trampoline(payload: *mut UnwindPayload);
-    #[cfg(not(feature = "nightly"))]
+    #[cfg(not(feature = "asm"))]
     fn unwind_lander(regs: *const LandingRegisters);
 }
 
-#[cfg(feature = "nightly")]
+#[cfg(feature = "asm")]
 #[naked]
 pub unsafe extern fn unwind_trampoline(_payload: *mut UnwindPayload) {
     asm!("
@@ -34,7 +34,7 @@ pub unsafe extern fn unwind_trampoline(_payload: *mut UnwindPayload) {
     ::std::hint::unreachable_unchecked();
 }
 
-#[cfg(feature = "nightly")]
+#[cfg(feature = "asm")]
 #[naked]
 unsafe extern fn unwind_lander(_regs: *const LandingRegisters) {
     asm!("

unwind/src/lib.rs

@@ -1,4 +1,5 @@
-#![cfg_attr(feature = "nightly", feature(asm, naked_functions))]
+#![cfg_attr(feature = "nightly", feature(unwind_attributes))]
+#![cfg_attr(feature = "asm", feature(asm, naked_functions))]
 
 extern crate gimli;
 extern crate libc;

unwind/src/libunwind_shim.rs

@@ -54,6 +54,8 @@ pub type _Unwind_Trace_Fn = extern "C" fn(ctx: *mut _Unwind_Context, arg: *mut c
                                           -> _Unwind_Reason_Code;
 type PersonalityRoutine = extern "C" fn(version: c_int, actions: c_int, class: u64, object: *mut _Unwind_Exception, context: *mut _Unwind_Context) -> _Unwind_Reason_Code;
 
+// FIXME: we skip over this function when unwinding, so we should ensure
+// it never needs any cleanup. Currently this is not true.
 #[no_mangle]
 pub unsafe extern "C" fn _Unwind_Resume(exception: *mut _Unwind_Exception) -> ! {
     DwarfUnwinder::default().trace(|frames| unwind_tracer(frames, exception));
@@ -108,6 +110,13 @@ pub unsafe extern "C" fn _Unwind_FindEnclosingFunction(pc: *mut c_void) -> *mut
     pc // FIXME: implement this
 }
 
+// FIXME: Set `unwind(allowed)` because we need to be able to unwind this function as
+// part of its operation. But this means any panics in this function are undefined
+// behaviour, and we don't currently ensure it doesn't panic.
+//
+// On stable (1.32), `unwind(allowed)` is the default, but this will change in 1.33, with
+// no stable way of setting `unwind(allowed)`, so this function will always abort in 1.33.
+#[cfg_attr(feature = "nightly", unwind(allowed))]
 #[no_mangle]
 pub unsafe extern "C" fn _Unwind_RaiseException(exception: *mut _Unwind_Exception) -> _Unwind_Reason_Code {
     (*exception).private_contptr = None;