Mark all extern functions as nounwind

Unwinding across an FFI boundary is undefined behaviour, so we can mark
all external function as nounwind. The obvious exception are those
functions that actually perform the unwinding.

src/libcore/lib.rs

@@ -79,6 +79,7 @@
 #![feature(optin_builtin_traits)]
 #![feature(reflect)]
 #![feature(rustc_attrs)]
+#![feature(unwind_attributes)]
 #![cfg_attr(stage0, feature(simd))]
 #![cfg_attr(not(stage0), feature(repr_simd, platform_intrinsics))]
 #![feature(staged_api)]

src/libcore/panicking.rs

@@ -62,6 +62,7 @@ pub fn panic_fmt(fmt: fmt::Arguments, file_line: &(&'static str, u32)) -> ! {
     #[allow(improper_ctypes)]
     extern {
         #[lang = "panic_fmt"]
+        #[unwind]
         fn panic_impl(fmt: fmt::Arguments, file: &'static str, line: u32) -> !;
     }
     let (file, line) = *file_line;

src/librustc_trans/trans/foreign.rs

@@ -211,6 +211,7 @@ pub fn register_foreign_item_fn<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
     let llfn_ty = lltype_for_fn_from_foreign_types(ccx, &tys);
 
     let llfn = get_extern_fn(ccx, &mut *ccx.externs().borrow_mut(), name, cc, llfn_ty, fty);
+    attributes::unwind(llfn, false);
     add_argument_attributes(&tys, llfn);
     attributes::from_fn_attrs(ccx, attrs, llfn);
     llfn

src/libstd/lib.rs

@@ -243,6 +243,7 @@
 #![feature(unique)]
 #![feature(unsafe_no_drop_flag, filling_drop)]
 #![feature(decode_utf16)]
+#![feature(unwind_attributes)]
 #![feature(vec_push_all)]
 #![feature(vec_resize)]
 #![feature(wrapping)]

src/libstd/sys/common/libunwind.rs

@@ -124,10 +124,12 @@ pub enum _Unwind_Context {}
     // iOS on armv7 uses SjLj exceptions and requires to link
     // against corresponding routine (..._SjLj_...)
     #[cfg(not(all(target_os = "ios", target_arch = "arm")))]
+    #[unwind]
     pub fn _Unwind_RaiseException(exception: *mut _Unwind_Exception)
                                   -> _Unwind_Reason_Code;
 
     #[cfg(all(target_os = "ios", target_arch = "arm"))]
+    #[unwind]
     fn _Unwind_SjLj_RaiseException(e: *mut _Unwind_Exception)
                                    -> _Unwind_Reason_Code;
 

src/libstd/sys/common/unwind/mod.rs

@@ -192,6 +192,7 @@ fn rust_panic(cause: Box<Any + Send + 'static>) -> ! {
 #[cfg(not(test))]
 /// Entry point of panic from the libcore crate.
 #[lang = "panic_fmt"]
+#[unwind]
 pub extern fn rust_begin_unwind(msg: fmt::Arguments,
                                 file: &'static str, line: u32) -> ! {
     begin_unwind_fmt(msg, &(file, line))

src/libstd/sys/common/unwind/seh.rs

@@ -62,6 +62,7 @@
 
 // This function is provided by kernel32.dll
 extern "system" {
+    #[unwind]
     fn RaiseException(dwExceptionCode: DWORD,
                       dwExceptionFlags: DWORD,
                       nNumberOfArguments: DWORD,

src/libstd/sys/common/unwind/seh64_gnu.rs

@@ -93,6 +93,7 @@ pub enum EXCEPTION_DISPOSITION {
 
 // From kernel32.dll
 extern "system" {
+    #[unwind]
     fn RaiseException(dwExceptionCode: DWORD,
                       dwExceptionFlags: DWORD,
                       nNumberOfArguments: DWORD,
@@ -198,6 +199,7 @@ pub unsafe fn cleanup(ptr: *mut u8) -> Box<Any + Send + 'static> {
 
 #[lang = "eh_unwind_resume"]
 #[cfg(not(test))]
+#[unwind]
 unsafe extern fn rust_eh_unwind_resume(panic_ctx: LPVOID) {
     let params = [panic_ctx as ULONG_PTR];
     RaiseException(RUST_PANIC,

src/test/codegen/extern-functions.rs

+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -C no-prepopulate-passes
+
+#![feature(unwind_attributes)]
+
+extern {
+// CHECK: Function Attrs: nounwind
+// CHECK-NEXT: declare void @extern_fn
+    fn extern_fn();
+// CHECK-NOT: Function Attrs: nounwind
+// CHECK: declare void @unwinding_extern_fn
+    #[unwind]
+    fn unwinding_extern_fn();
+}