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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-exception6//7//8// Implements Wasm exception handling proposal9// (https://github.com/WebAssembly/exception-handling) based C++ exceptions10//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 function29 uintptr_t lpad_index; // landing pad index30 uintptr_t lsda; // LSDA address31 32 // Output information computed by personality function33 uintptr_t selector; // selector value34};35 36// Communication channel between compiler-generated user code and personality37// function38thread_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, which42/// calls the personality function for each each frame it lands. On the other43/// hand, WebAssembly stack unwinding process is performed by a VM, and the44/// personality function cannot be called from there. So the compiler inserts45/// a call to this function in landing pads in the user code, which in turn46/// 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 we57 // 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_Code65_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 void74_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, which88 // 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 we96 // increment 2 here97 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_t109_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