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 __USING_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
27 struct _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
38 thread_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.
_Unwind_CallPersonality(void * exception_ptr)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
_Unwind_RaiseException(_Unwind_Exception * exception_object)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
_Unwind_DeleteException(_Unwind_Exception * exception_object)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.
_Unwind_SetGR(struct _Unwind_Context * context,int index,uintptr_t value)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.
_Unwind_GetIP(struct _Unwind_Context * context)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.
_Unwind_SetIP(struct _Unwind_Context * context,uintptr_t value)105 _LIBUNWIND_EXPORT void _Unwind_SetIP(struct _Unwind_Context *context,
106 uintptr_t value) {}
107
108 /// Called by personality handler to get LSDA for current frame.
109 _LIBUNWIND_EXPORT uintptr_t
_Unwind_GetLanguageSpecificData(struct _Unwind_Context * context)110 _Unwind_GetLanguageSpecificData(struct _Unwind_Context *context) {
111 uintptr_t result = ((struct _Unwind_LandingPadContext *)context)->lsda;
112 _LIBUNWIND_TRACE_API("_Unwind_GetLanguageSpecificData(context=%p) => 0x%lx",
113 (void *)context, result);
114 return result;
115 }
116
117 /// Not used in Wasm.
118 _LIBUNWIND_EXPORT uintptr_t
_Unwind_GetRegionStart(struct _Unwind_Context * context)119 _Unwind_GetRegionStart(struct _Unwind_Context *context) {
120 return 0;
121 }
122
123 #endif // defined(__USING_WASM_EXCEPTIONS__)
124