1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
|
//! Unwinding for *emscripten* target.
//!
//! Whereas Rust's usual unwinding implementation for Unix platforms
//! calls into the libunwind APIs directly, on Emscripten we instead
//! call into the C++ unwinding APIs. This is just an expedience since
//! Emscripten's runtime always implements those APIs and does not
//! implement libunwind.
use alloc::boxed::Box;
use core::any::Any;
use core::intrinsics;
use core::mem;
use core::ptr;
use core::sync::atomic::{AtomicBool, Ordering};
use libc::{self, c_int};
use unwind as uw;
// This matches the layout of std::type_info in C++
#[repr(C)]
struct TypeInfo {
vtable: *const usize,
name: *const u8,
}
unsafe impl Sync for TypeInfo {}
extern "C" {
// The leading `\x01` byte here is actually a magical signal to LLVM to
// *not* apply any other mangling like prefixing with a `_` character.
//
// This symbol is the vtable used by C++'s `std::type_info`. Objects of type
// `std::type_info`, type descriptors, have a pointer to this table. Type
// descriptors are referenced by the C++ EH structures defined above and
// that we construct below.
//
// Note that the real size is larger than 3 usize, but we only need our
// vtable to point to the third element.
#[link_name = "\x01_ZTVN10__cxxabiv117__class_type_infoE"]
static CLASS_TYPE_INFO_VTABLE: [usize; 3];
}
// std::type_info for a rust_panic class
#[lang = "eh_catch_typeinfo"]
static EXCEPTION_TYPE_INFO: TypeInfo = TypeInfo {
// Normally we would use .as_ptr().add(2) but this doesn't work in a const context.
vtable: unsafe { &CLASS_TYPE_INFO_VTABLE[2] },
// This intentionally doesn't use the normal name mangling scheme because
// we don't want C++ to be able to produce or catch Rust panics.
name: b"rust_panic\0".as_ptr(),
};
struct Exception {
// This is necessary because C++ code can capture our exception with
// std::exception_ptr and rethrow it multiple times, possibly even in
// another thread.
caught: AtomicBool,
// This needs to be an Option because the object's lifetime follows C++
// semantics: when catch_unwind moves the Box out of the exception it must
// still leave the exception object in a valid state because its destructor
// is still going to be called by __cxa_end_catch.
data: Option<Box<dyn Any + Send>>,
}
pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
// intrinsics::try actually gives us a pointer to this structure.
#[repr(C)]
struct CatchData {
ptr: *mut u8,
is_rust_panic: bool,
}
let catch_data = &*(ptr as *mut CatchData);
let adjusted_ptr = __cxa_begin_catch(catch_data.ptr as *mut libc::c_void) as *mut Exception;
let out = if catch_data.is_rust_panic {
let was_caught = (*adjusted_ptr).caught.swap(true, Ordering::SeqCst);
if was_caught {
// Since cleanup() isn't allowed to panic, we just abort instead.
intrinsics::abort();
}
(*adjusted_ptr).data.take().unwrap()
} else {
super::__rust_foreign_exception();
};
__cxa_end_catch();
out
}
pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
let sz = mem::size_of_val(&data);
let exception = __cxa_allocate_exception(sz) as *mut Exception;
if exception.is_null() {
return uw::_URC_FATAL_PHASE1_ERROR as u32;
}
ptr::write(exception, Exception { caught: AtomicBool::new(false), data: Some(data) });
__cxa_throw(exception as *mut _, &EXCEPTION_TYPE_INFO, exception_cleanup);
}
extern "C" fn exception_cleanup(ptr: *mut libc::c_void) -> *mut libc::c_void {
unsafe {
if let Some(b) = (ptr as *mut Exception).read().data {
drop(b);
super::__rust_drop_panic();
}
ptr
}
}
// This is required by the compiler to exist (e.g., it's a lang item), but it's
// never actually called by the compiler. Emscripten EH doesn't use a
// personality function at all, it instead uses __cxa_find_matching_catch.
// Wasm error handling would use __gxx_personality_wasm0.
#[lang = "eh_personality"]
unsafe extern "C" fn rust_eh_personality(
_version: c_int,
_actions: uw::_Unwind_Action,
_exception_class: uw::_Unwind_Exception_Class,
_exception_object: *mut uw::_Unwind_Exception,
_context: *mut uw::_Unwind_Context,
) -> uw::_Unwind_Reason_Code {
core::intrinsics::abort()
}
extern "C" {
fn __cxa_allocate_exception(thrown_size: libc::size_t) -> *mut libc::c_void;
fn __cxa_begin_catch(thrown_exception: *mut libc::c_void) -> *mut libc::c_void;
fn __cxa_end_catch();
fn __cxa_throw(
thrown_exception: *mut libc::c_void,
tinfo: *const TypeInfo,
dest: extern "C" fn(*mut libc::c_void) -> *mut libc::c_void,
) -> !;
}
|
