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. 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 *context, 106 uintptr_t value) {} 107 108 /// Called by personality handler to get LSDA for current frame. 109 _LIBUNWIND_EXPORT uintptr_t 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 119 _Unwind_GetRegionStart(struct _Unwind_Context *context) { 120 return 0; 121 } 122 123 #endif // defined(__USING_WASM_EXCEPTIONS__) 124