1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//
8// Implements Wasm exception handling proposal
9// (https://github.com/WebAssembly/exception-handling) based C++ exceptions
10//
11//===----------------------------------------------------------------------===//
12
13#include <stdbool.h>
14
15#include "config.h"
16
17#ifdef __WASM_EXCEPTIONS__
18
19#include "unwind.h"
20#include <threads.h>
21
22_Unwind_Reason_Code __gxx_personality_wasm0(int version, _Unwind_Action actions,
23 uint64_t exceptionClass,
24 _Unwind_Exception *unwind_exception,
25 _Unwind_Context *context);
26
27struct _Unwind_LandingPadContext {
28 // Input information to personality function
29 uintptr_t lpad_index; // landing pad index
30 uintptr_t lsda; // LSDA address
31
32 // Output information computed by personality function
33 uintptr_t selector; // selector value
34};
35
36// Communication channel between compiler-generated user code and personality
37// function
38thread_local struct _Unwind_LandingPadContext __wasm_lpad_context;
39
40/// Calls to this function is in landing pads in compiler-generated user code.
41/// In other EH schemes, stack unwinding is done by libunwind library, which
42/// calls the personality function for each each frame it lands. On the other
43/// hand, WebAssembly stack unwinding process is performed by a VM, and the
44/// personality function cannot be called from there. So the compiler inserts
45/// a call to this function in landing pads in the user code, which in turn
46/// calls the personality function.
47_Unwind_Reason_Code _Unwind_CallPersonality(void *exception_ptr) {
48 struct _Unwind_Exception *exception_object =
49 (struct _Unwind_Exception *)exception_ptr;
50 _LIBUNWIND_TRACE_API("_Unwind_CallPersonality(exception_object=%p)",
51 (void *)exception_object);
52
53 // Reset the selector.
54 __wasm_lpad_context.selector = 0;
55
56 // Call personality function. Wasm does not have two-phase unwinding, so we
57 // only do the cleanup phase.
58 return __gxx_personality_wasm0(
59 1, _UA_SEARCH_PHASE, exception_object->exception_class, exception_object,
60 (struct _Unwind_Context *)&__wasm_lpad_context);
61}
62
63/// Called by __cxa_throw.
64_LIBUNWIND_EXPORT _Unwind_Reason_Code
65_Unwind_RaiseException(_Unwind_Exception *exception_object) {
66 _LIBUNWIND_TRACE_API("_Unwind_RaiseException(exception_object=%p)",
67 (void *)exception_object);
68 // Use Wasm EH's 'throw' instruction.
69 __builtin_wasm_throw(0, exception_object);
70}
71
72/// Called by __cxa_end_catch.
73_LIBUNWIND_EXPORT void
74_Unwind_DeleteException(_Unwind_Exception *exception_object) {
75 _LIBUNWIND_TRACE_API("_Unwind_DeleteException(ex_obj=%p)",
76 (void *)(exception_object));
77 if (exception_object->exception_cleanup != NULL)
78 (*exception_object->exception_cleanup)(_URC_FOREIGN_EXCEPTION_CAUGHT,
79 exception_object);
80}
81
82/// Called by personality handler to alter register values.
83_LIBUNWIND_EXPORT void _Unwind_SetGR(struct _Unwind_Context *context, int index,
84 uintptr_t value) {
85 _LIBUNWIND_TRACE_API("_Unwind_SetGR(context=%p, index=%d, value=%lu)",
86 (void *)context, index, value);
87 // We only use this function to set __wasm_lpad_context.selector field, which
88 // is index 1 in the personality function.
89 if (index == 1)
90 ((struct _Unwind_LandingPadContext *)context)->selector = value;
91}
92
93/// Called by personality handler to get instruction pointer.
94_LIBUNWIND_EXPORT uintptr_t _Unwind_GetIP(struct _Unwind_Context *context) {
95 // The result will be used as an 1-based index after decrementing 1, so we
96 // increment 2 here
97 uintptr_t result =
98 ((struct _Unwind_LandingPadContext *)context)->lpad_index + 2;
99 _LIBUNWIND_TRACE_API("_Unwind_GetIP(context=%p) => %lu", (void *)context,
100 result);
101 return result;
102}
103
104/// Not used in Wasm.
105_LIBUNWIND_EXPORT void _Unwind_SetIP(struct _Unwind_Context *, uintptr_t) {}
106
107/// Called by personality handler to get LSDA for current frame.
108_LIBUNWIND_EXPORT uintptr_t
109_Unwind_GetLanguageSpecificData(struct _Unwind_Context *context) {
110 uintptr_t result = ((struct _Unwind_LandingPadContext *)context)->lsda;
111 _LIBUNWIND_TRACE_API("_Unwind_GetLanguageSpecificData(context=%p) => 0x%lx",
112 (void *)context, result);
113 return result;
114}
115
116/// Not used in Wasm.
117_LIBUNWIND_EXPORT uintptr_t _Unwind_GetRegionStart(struct _Unwind_Context *) {
118 return 0;
119}
120
121#endif // defined(__WASM_EXCEPTIONS__)
122