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
133
134
135
136
137
138
|
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//
// Implements Wasm exception handling proposal
// (https://github.com/WebAssembly/exception-handling) based C++ exceptions
//
//===----------------------------------------------------------------------===//
#include <stdbool.h>
#include "config.h"
#include "unwind.h"
#ifdef __WASM_EXCEPTIONS__
#include <threads.h>
_Unwind_Reason_Code __gxx_personality_wasm0(int version, _Unwind_Action actions,
uint64_t exceptionClass,
_Unwind_Exception *unwind_exception,
_Unwind_Context *context);
struct _Unwind_LandingPadContext {
// Input information to personality function
uintptr_t lpad_index; // landing pad index
uintptr_t lsda; // LSDA address
// Output information computed by personality function
uintptr_t selector; // selector value
};
// Communication channel between compiler-generated user code and personality
// function
thread_local struct _Unwind_LandingPadContext __wasm_lpad_context;
/// Calls to this function is in landing pads in compiler-generated user code.
/// In other EH schemes, stack unwinding is done by libunwind library, which
/// calls the personality function for each each frame it lands. On the other
/// hand, WebAssembly stack unwinding process is performed by a VM, and the
/// personality function cannot be called from there. So the compiler inserts
/// a call to this function in landing pads in the user code, which in turn
/// calls the personality function.
_Unwind_Reason_Code _Unwind_CallPersonality(void *exception_ptr) {
struct _Unwind_Exception *exception_object =
(struct _Unwind_Exception *)exception_ptr;
_LIBUNWIND_TRACE_API("_Unwind_CallPersonality(exception_object=%p)",
(void *)exception_object);
// Reset the selector.
__wasm_lpad_context.selector = 0;
// Call personality function. Wasm does not have two-phase unwinding, so we
// only do the cleanup phase.
return __gxx_personality_wasm0(
1, _UA_SEARCH_PHASE, exception_object->exception_class, exception_object,
(struct _Unwind_Context *)&__wasm_lpad_context);
}
/// Called by __cxa_throw.
_LIBUNWIND_EXPORT _Unwind_Reason_Code
_Unwind_RaiseException(_Unwind_Exception *exception_object) {
_LIBUNWIND_TRACE_API("_Unwind_RaiseException(exception_object=%p)",
(void *)exception_object);
// Use Wasm EH's 'throw' instruction.
__builtin_wasm_throw(0, exception_object);
}
/// Called by __cxa_end_catch.
_LIBUNWIND_EXPORT void
_Unwind_DeleteException(_Unwind_Exception *exception_object) {
_LIBUNWIND_TRACE_API("_Unwind_DeleteException(ex_obj=%p)",
(void *)(exception_object));
if (exception_object->exception_cleanup != NULL)
(*exception_object->exception_cleanup)(_URC_FOREIGN_EXCEPTION_CAUGHT,
exception_object);
}
/// Called by personality handler to alter register values.
_LIBUNWIND_EXPORT void _Unwind_SetGR(struct _Unwind_Context *context, int index,
uintptr_t value) {
_LIBUNWIND_TRACE_API("_Unwind_SetGR(context=%p, index=%d, value=%lu)",
(void *)context, index, value);
// We only use this function to set __wasm_lpad_context.selector field, which
// is index 1 in the personality function.
if (index == 1)
((struct _Unwind_LandingPadContext *)context)->selector = value;
}
/// Called by personality handler to get instruction pointer.
_LIBUNWIND_EXPORT uintptr_t _Unwind_GetIP(struct _Unwind_Context *context) {
// The result will be used as an 1-based index after decrementing 1, so we
// increment 2 here
uintptr_t result =
((struct _Unwind_LandingPadContext *)context)->lpad_index + 2;
_LIBUNWIND_TRACE_API("_Unwind_GetIP(context=%p) => %lu", (void *)context,
result);
return result;
}
/// Not used in Wasm.
_LIBUNWIND_EXPORT void _Unwind_SetIP(struct _Unwind_Context *context __attribute__((unused)),
uintptr_t value __attribute__((unused))) {}
/// Called by personality handler to get LSDA for current frame.
_LIBUNWIND_EXPORT uintptr_t
_Unwind_GetLanguageSpecificData(struct _Unwind_Context *context) {
uintptr_t result = ((struct _Unwind_LandingPadContext *)context)->lsda;
_LIBUNWIND_TRACE_API("_Unwind_GetLanguageSpecificData(context=%p) => 0x%lx",
(void *)context, result);
return result;
}
/// Not used in Wasm.
_LIBUNWIND_EXPORT uintptr_t
_Unwind_GetRegionStart(struct _Unwind_Context *context __attribute__((unused))) {
return 0;
}
#elif defined(__EMSCRIPTEN__)
/// Called by __cxa_throw.
/// Define it here to prevent linker errors if we're buildingig Wasm modules
/// without exception support.
_LIBUNWIND_EXPORT _Unwind_Reason_Code
_Unwind_RaiseException(_Unwind_Exception *exception_object __attribute__((unused))) {
abort();
}
#if !defined(NDEBUG) && defined(STANDALONE_WASM)
void __throw_exception_with_stack_trace(_Unwind_Exception* ex) {
_Unwind_RaiseException(ex);
}
#endif
#endif // defined(__WASM_EXCEPTIONS__)
|
