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 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 *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