1 //! Unwinding for *emscripten* target.
3 //! Whereas Rust's usual unwinding implementation for Unix platforms
4 //! calls into the libunwind APIs directly, on Emscripten we instead
5 //! call into the C++ unwinding APIs. This is just an expedience since
6 //! Emscripten's runtime always implements those APIs and does not
7 //! implement libunwind.
9 #![allow(private_no_mangle_fns)]
11 use alloc::boxed::Box;
15 use libc::{self, c_int};
18 // This matches the layout of std::type_info in C++
24 unsafe impl Sync for TypeInfo {}
27 // The leading `\x01` byte here is actually a magical signal to LLVM to
28 // *not* apply any other mangling like prefixing with a `_` character.
30 // This symbol is the vtable used by C++'s `std::type_info`. Objects of type
31 // `std::type_info`, type descriptors, have a pointer to this table. Type
32 // descriptors are referenced by the C++ EH structures defined above and
33 // that we construct below.
35 // Note that the real size is larger than 3 usize, but we only need our
36 // vtable to point to the third element.
37 #[link_name = "\x01_ZTVN10__cxxabiv117__class_type_infoE"]
38 static CLASS_TYPE_INFO_VTABLE: [usize; 3];
41 // std::type_info for a rust_panic class
42 #[lang = "eh_catch_typeinfo"]
43 static EXCEPTION_TYPE_INFO: TypeInfo = TypeInfo {
44 // Normally we would use .as_ptr().add(2) but this doesn't work in a const context.
45 vtable: unsafe { &CLASS_TYPE_INFO_VTABLE[2] },
46 // This intentionally doesn't use the normal name mangling scheme because
47 // we don't want C++ to be able to produce or catch Rust panics.
48 name: b"rust_panic\0".as_ptr(),
51 pub type Payload = *mut u8;
54 // This needs to be an Option because the object's lifetime follows C++
55 // semantics: when catch_unwind moves the Box out of the exception it must
56 // still leave the exception object in a valid state because its destructor
57 // is still going to be called by __cxa_end_catch..
58 data: Option<Box<dyn Any + Send>>,
61 pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
62 assert!(!ptr.is_null());
63 let adjusted_ptr = __cxa_begin_catch(ptr as *mut libc::c_void) as *mut Exception;
64 let ex = (*adjusted_ptr).data.take();
69 pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
70 let sz = mem::size_of_val(&data);
71 let exception = __cxa_allocate_exception(sz) as *mut Exception;
72 if exception.is_null() {
73 return uw::_URC_FATAL_PHASE1_ERROR as u32;
75 ptr::write(exception, Exception { data: Some(data) });
76 __cxa_throw(exception as *mut _, &EXCEPTION_TYPE_INFO, exception_cleanup);
79 // On WASM and ARM, the destructor returns the pointer to the object.
81 if #[cfg(any(target_arch = "arm", target_arch = "wasm32"))] {
82 type DestructorRet = *mut libc::c_void;
84 type DestructorRet = ();
87 extern "C" fn exception_cleanup(ptr: *mut libc::c_void) -> DestructorRet {
89 if let Some(b) = (ptr as *mut Exception).read().data {
91 super::__rust_drop_panic();
93 #[cfg(any(target_arch = "arm", target_arch = "wasm32"))]
98 #[lang = "eh_personality"]
100 unsafe extern "C" fn rust_eh_personality(
102 actions: uw::_Unwind_Action,
103 exception_class: uw::_Unwind_Exception_Class,
104 exception_object: *mut uw::_Unwind_Exception,
105 context: *mut uw::_Unwind_Context,
106 ) -> uw::_Unwind_Reason_Code {
107 __gxx_personality_v0(version, actions, exception_class, exception_object, context)
111 fn __cxa_allocate_exception(thrown_size: libc::size_t) -> *mut libc::c_void;
112 fn __cxa_begin_catch(thrown_exception: *mut libc::c_void) -> *mut libc::c_void;
113 fn __cxa_end_catch();
115 thrown_exception: *mut libc::c_void,
116 tinfo: *const TypeInfo,
117 dest: extern "C" fn(*mut libc::c_void) -> DestructorRet,
119 fn __gxx_personality_v0(
121 actions: uw::_Unwind_Action,
122 exception_class: uw::_Unwind_Exception_Class,
123 exception_object: *mut uw::_Unwind_Exception,
124 context: *mut uw::_Unwind_Context,
125 ) -> uw::_Unwind_Reason_Code;