1284990Scy//===----------------------------------------------------------------------===// 2284990Scy// 3284990Scy// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4284990Scy// See https://llvm.org/LICENSE.txt for license information. 5284990Scy// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6284990Scy// 7284990Scy// 8284990Scy// Implements Wasm exception handling proposal 9284990Scy// (https://github.com/WebAssembly/exception-handling) based C++ exceptions 10284990Scy// 11284990Scy//===----------------------------------------------------------------------===// 12284990Scy 13284990Scy#include <stdbool.h> 14284990Scy 15284990Scy#include "config.h" 16284990Scy 17284990Scy#ifdef __USING_WASM_EXCEPTIONS__ 18284990Scy 19284990Scy#include "unwind.h" 20284990Scy#include <threads.h> 21284990Scy 22284990Scy_Unwind_Reason_Code __gxx_personality_wasm0(int version, _Unwind_Action actions, 23284990Scy uint64_t exceptionClass, 24284990Scy _Unwind_Exception *unwind_exception, 25284990Scy _Unwind_Context *context); 26284990Scy 27284990Scystruct _Unwind_LandingPadContext { 28284990Scy // Input information to personality function 29284990Scy uintptr_t lpad_index; // landing pad index 30284990Scy uintptr_t lsda; // LSDA address 31284990Scy 32284990Scy // Output information computed by personality function 33284990Scy uintptr_t selector; // selector value 34284990Scy}; 35284990Scy 36284990Scy// Communication channel between compiler-generated user code and personality 37284990Scy// function 38284990Scythread_local struct _Unwind_LandingPadContext __wasm_lpad_context; 39284990Scy 40284990Scy/// Calls to this function is in landing pads in compiler-generated user code. 41284990Scy/// In other EH schemes, stack unwinding is done by libunwind library, which 42284990Scy/// calls the personality function for each each frame it lands. On the other 43284990Scy/// hand, WebAssembly stack unwinding process is performed by a VM, and the 44284990Scy/// personality function cannot be called from there. So the compiler inserts 45284990Scy/// a call to this function in landing pads in the user code, which in turn 46284990Scy/// calls the personality function. 47284990Scy_Unwind_Reason_Code _Unwind_CallPersonality(void *exception_ptr) { 48284990Scy struct _Unwind_Exception *exception_object = 49284990Scy (struct _Unwind_Exception *)exception_ptr; 50284990Scy _LIBUNWIND_TRACE_API("_Unwind_CallPersonality(exception_object=%p)", 51284990Scy (void *)exception_object); 52284990Scy 53284990Scy // Reset the selector. 54284990Scy __wasm_lpad_context.selector = 0; 55284990Scy 56284990Scy // Call personality function. Wasm does not have two-phase unwinding, so we 57284990Scy // only do the cleanup phase. 58284990Scy return __gxx_personality_wasm0( 59284990Scy 1, _UA_SEARCH_PHASE, exception_object->exception_class, exception_object, 60284990Scy (struct _Unwind_Context *)&__wasm_lpad_context); 61284990Scy} 62284990Scy 63284990Scy/// Called by __cxa_throw. 64284990Scy_LIBUNWIND_EXPORT _Unwind_Reason_Code 65284990Scy_Unwind_RaiseException(_Unwind_Exception *exception_object) { 66284990Scy _LIBUNWIND_TRACE_API("_Unwind_RaiseException(exception_object=%p)", 67284990Scy (void *)exception_object); 68284990Scy // Use Wasm EH's 'throw' instruction. 69284990Scy __builtin_wasm_throw(0, exception_object); 70284990Scy} 71284990Scy 72284990Scy/// Called by __cxa_end_catch. 73284990Scy_LIBUNWIND_EXPORT void 74284990Scy_Unwind_DeleteException(_Unwind_Exception *exception_object) { 75284990Scy _LIBUNWIND_TRACE_API("_Unwind_DeleteException(ex_obj=%p)", 76284990Scy (void *)(exception_object)); 77284990Scy if (exception_object->exception_cleanup != NULL) 78284990Scy (*exception_object->exception_cleanup)(_URC_FOREIGN_EXCEPTION_CAUGHT, 79284990Scy exception_object); 80284990Scy} 81284990Scy 82284990Scy/// Called by personality handler to alter register values. 83284990Scy_LIBUNWIND_EXPORT void _Unwind_SetGR(struct _Unwind_Context *context, int index, 84284990Scy uintptr_t value) { 85284990Scy _LIBUNWIND_TRACE_API("_Unwind_SetGR(context=%p, index=%d, value=%lu)", 86284990Scy (void *)context, index, value); 87284990Scy // We only use this function to set __wasm_lpad_context.selector field, which 88284990Scy // is index 1 in the personality function. 89284990Scy if (index == 1) 90284990Scy ((struct _Unwind_LandingPadContext *)context)->selector = value; 91284990Scy} 92284990Scy 93284990Scy/// Called by personality handler to get instruction pointer. 94284990Scy_LIBUNWIND_EXPORT uintptr_t _Unwind_GetIP(struct _Unwind_Context *context) { 95284990Scy // The result will be used as an 1-based index after decrementing 1, so we 96284990Scy // increment 2 here 97284990Scy uintptr_t result = 98284990Scy ((struct _Unwind_LandingPadContext *)context)->lpad_index + 2; 99284990Scy _LIBUNWIND_TRACE_API("_Unwind_GetIP(context=%p) => %lu", (void *)context, 100284990Scy result); 101284990Scy return result; 102284990Scy} 103284990Scy 104284990Scy/// Not used in Wasm. 105284990Scy_LIBUNWIND_EXPORT void _Unwind_SetIP(struct _Unwind_Context *context, 106284990Scy uintptr_t value) {} 107284990Scy 108284990Scy/// Called by personality handler to get LSDA for current frame. 109284990Scy_LIBUNWIND_EXPORT uintptr_t 110284990Scy_Unwind_GetLanguageSpecificData(struct _Unwind_Context *context) { 111284990Scy uintptr_t result = ((struct _Unwind_LandingPadContext *)context)->lsda; 112284990Scy _LIBUNWIND_TRACE_API("_Unwind_GetLanguageSpecificData(context=%p) => 0x%lx", 113284990Scy (void *)context, result); 114284990Scy return result; 115284990Scy} 116284990Scy 117284990Scy/// Not used in Wasm. 118284990Scy_LIBUNWIND_EXPORT uintptr_t 119284990Scy_Unwind_GetRegionStart(struct _Unwind_Context *context) { 120284990Scy return 0; 121284990Scy} 122284990Scy 123284990Scy#endif // defined(__USING_WASM_EXCEPTIONS__) 124284990Scy