iOS: Fix the longjmp/setjmp ffi (#613)

* iOS: Fix the `longjmp`/`setjmp` ffi. `jmp_buf` was the wrong size (too small) causing crashes on application launch, make longjmp return Never

* remove extra parentheses around JBLEN, and add a changelog entry about the JmpBuf fix

CHANGELOG.md

@@ -6,6 +6,7 @@
 - **Breaking:** On iOS, `UIView` is now the default root view. `WindowBuilderExt::with_root_view_class` can be used to set the root view objective-c class to `GLKView` (OpenGLES) or `MTKView` (Metal/MoltenVK).
 - On iOS, the `UIApplication` is not started until `Window::new` is called.
 - Fixed thread unsafety with cursor hiding on macOS.
+- On iOS, fixed the size of the `JmpBuf` type used for `setjmp`/`longjmp` calls. Previously this was a buffer overflow on most architectures.
 
 # Version 0.16.2 (2018-07-07)
 

src/platform/ios/ffi.rs

@@ -64,10 +64,20 @@ extern {
 
 extern {
     pub fn setjmp(env: *mut c_void) -> c_int;
-    pub fn longjmp(env: *mut c_void, val: c_int);
+    pub fn longjmp(env: *mut c_void, val: c_int) -> !;
 }
 
-pub type JmpBuf = [c_int; 27];
+// values taken from "setjmp.h" header in xcode iPhoneOS/iPhoneSimulator SDK
+#[cfg(any(target_arch = "x86_64"))]
+pub const JBLEN: usize = (9 * 2) + 3 + 16;
+#[cfg(any(target_arch = "x86"))]
+pub const JBLEN: usize = 18;
+#[cfg(target_arch = "arm")]
+pub const JBLEN: usize = 10 + 16 + 2;
+#[cfg(target_arch = "aarch64")]
+pub const JBLEN: usize = (14 + 8 + 2) * 2;
+
+pub type JmpBuf = [c_int; JBLEN];
 
 pub trait NSString: Sized {
     unsafe fn alloc(_: Self) -> id {

src/platform/ios/mod.rs

@@ -92,6 +92,7 @@ use self::ffi::{
     CGPoint,
     CGRect,
     id,
+    JBLEN,
     JmpBuf,
     kCFRunLoopDefaultMode,
     kCFRunLoopRunHandledSource,
@@ -209,7 +210,7 @@ impl EventsLoop {
     pub fn new() -> EventsLoop {
         unsafe {
             if !msg_send![class!(NSThread), isMainThread] {
-                panic!("`Window` can only be created on the main thread on iOS");
+                panic!("`EventsLoop` can only be created on the main thread on iOS");
             }
         }
         EventsLoop { events_queue: Default::default() }
@@ -315,7 +316,7 @@ impl Window {
     ) -> Result<Window, CreationError> {
         unsafe {
             debug_assert!(mem::size_of_val(&JMPBUF) == mem::size_of::<Box<JmpBuf>>());
-            assert!(mem::replace(&mut JMPBUF, Some(Box::new([0; 27]))).is_none(), "Only one `Window` is supported on iOS");
+            assert!(mem::replace(&mut JMPBUF, Some(Box::new([0; JBLEN]))).is_none(), "Only one `Window` is supported on iOS");
         }
 
         unsafe {