make `#[unwind]` attribute specify expectations more clearly

You can now choose between the following:

- `#[unwind(allowed)]`
- `#[unwind(aborts)]`

Per rust-lang/rust#48251, the default is `#[unwind(allowed)]`, though
I think we should change this eventually.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/libstd/panicking.rs b/src/libstd/panicking.rs
index 161c3fc7113..454ac64735c 100644
--- a/src/libstd/panicking.rs
+++ b/src/libstd/panicking.rs
@@ -55,7 +55,8 @@ extern {
                                 data: *mut u8,
                                 data_ptr: *mut usize,
                                 vtable_ptr: *mut usize) -> u32;
-    #[unwind]
+    #[cfg_attr(stage0, unwind)]
+    #[cfg_attr(not(stage0), unwind(allowed))]
     fn __rust_start_panic(data: usize, vtable: usize) -> u32;
 }
 
@@ -315,7 +316,8 @@ pub fn panicking() -> bool {
 /// Entry point of panic from the libcore crate.
 #[cfg(not(test))]
 #[lang = "panic_fmt"]
-#[unwind]
+#[cfg_attr(stage0, unwind)]
+#[cfg_attr(not(stage0), unwind(allowed))]
 pub extern fn rust_begin_panic(msg: fmt::Arguments,
                                file: &'static str,
                                line: u32,