diff --git a/libunwind/src/Unwind-wasm.c b/libunwind/src/Unwind-wasm.c new file mode 100644 index 0000000000000..35f2f9aeab080 --- /dev/null +++ b/libunwind/src/Unwind-wasm.c @@ -0,0 +1,121 @@ +//===----------------------------------------------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +// +// Implements Wasm exception handling proposal +// (https://github.com/WebAssembly/exception-handling) based C++ exceptions +// +//===----------------------------------------------------------------------===// + +#include "config.h" +#include "unwind.h" +#include +#include + +#ifdef __USING_WASM_EXCEPTIONS__ + +_Unwind_Reason_Code __gxx_personality_wasm0(int version, _Unwind_Action actions, + uint64_t exceptionClass, + _Unwind_Exception *unwind_exception, + _Unwind_Context *context); + +struct _Unwind_LandingPadContext { + // Input information to personality function + uintptr_t lpad_index; // landing pad index + uintptr_t lsda; // LSDA address + + // Output information computed by personality function + uintptr_t selector; // selector value +}; + +// Communication channel between compiler-generated user code and personality +// function +thread_local struct _Unwind_LandingPadContext __wasm_lpad_context; + +/// Calls to this function is in landing pads in compiler-generated user code. +/// In other EH schemes, stack unwinding is done by libunwind library, which +/// calls the personality function for each each frame it lands. On the other +/// hand, WebAssembly stack unwinding process is performed by a VM, and the +/// personality function cannot be called from there. So the compiler inserts +/// a call to this function in landing pads in the user code, which in turn +/// calls the personality function. +_Unwind_Reason_Code _Unwind_CallPersonality(void *exception_ptr) { + struct _Unwind_Exception *exception_object = + (struct _Unwind_Exception *)exception_ptr; + _LIBUNWIND_TRACE_API("_Unwind_CallPersonality(exception_object=%p)", + (void *)exception_object); + + // Reset the selector. + __wasm_lpad_context.selector = 0; + + // Call personality function. Wasm does not have two-phase unwinding, so we + // only do the cleanup phase. + return __gxx_personality_wasm0( + 1, _UA_SEARCH_PHASE, exception_object->exception_class, exception_object, + (struct _Unwind_Context *)&__wasm_lpad_context); +} + +/// Called by __cxa_throw. +_LIBUNWIND_EXPORT _Unwind_Reason_Code +_Unwind_RaiseException(_Unwind_Exception *exception_object) { + _LIBUNWIND_TRACE_API("_Unwind_RaiseException(exception_object=%p)", + (void *)exception_object); + // Use Wasm EH's 'throw' instruction. + __builtin_wasm_throw(0, exception_object); +} + +/// Called by __cxa_end_catch. +_LIBUNWIND_EXPORT void +_Unwind_DeleteException(_Unwind_Exception *exception_object) { + _LIBUNWIND_TRACE_API("_Unwind_DeleteException(ex_obj=%p)", + (void *)(exception_object)); + if (exception_object->exception_cleanup != NULL) + (*exception_object->exception_cleanup)(_URC_FOREIGN_EXCEPTION_CAUGHT, + exception_object); +} + +/// Called by personality handler to alter register values. +_LIBUNWIND_EXPORT void _Unwind_SetGR(struct _Unwind_Context *context, int index, + uintptr_t value) { + _LIBUNWIND_TRACE_API("_Unwind_SetGR(context=%p, index=%d, value=%lu)", + (void *)context, index, value); + // We only use this function to set __wasm_lpad_context.selector field, which + // is index 1 in the personality function. + if (index == 1) + ((struct _Unwind_LandingPadContext *)context)->selector = value; +} + +/// Called by personality handler to get instruction pointer. +_LIBUNWIND_EXPORT uintptr_t _Unwind_GetIP(struct _Unwind_Context *context) { + // The result will be used as an 1-based index after decrementing 1, so we + // increment 2 here + uintptr_t result = + ((struct _Unwind_LandingPadContext *)context)->lpad_index + 2; + _LIBUNWIND_TRACE_API("_Unwind_GetIP(context=%p) => %lu", (void *)context, + result); + return result; +} + +/// Not used in Wasm. +_LIBUNWIND_EXPORT void _Unwind_SetIP(struct _Unwind_Context *context, + uintptr_t value) {} + +/// Called by personality handler to get LSDA for current frame. +_LIBUNWIND_EXPORT uintptr_t +_Unwind_GetLanguageSpecificData(struct _Unwind_Context *context) { + uintptr_t result = ((struct _Unwind_LandingPadContext *)context)->lsda; + _LIBUNWIND_TRACE_API("_Unwind_GetLanguageSpecificData(context=%p) => 0x%lx", + (void *)context, result); + return result; +} + +/// Not used in Wasm. +_LIBUNWIND_EXPORT uintptr_t +_Unwind_GetRegionStart(struct _Unwind_Context *context) { + return 0; +} + +#endif diff --git a/libunwind/src/config.h b/libunwind/src/config.h index a20bf43272cde..deb5a4d4d73d4 100644 --- a/libunwind/src/config.h +++ b/libunwind/src/config.h @@ -89,7 +89,7 @@ __asm__(".globl " SYMBOL_NAME(aliasname)); \ __asm__(SYMBOL_NAME(aliasname) " = " SYMBOL_NAME(name)); \ _LIBUNWIND_ALIAS_VISIBILITY(SYMBOL_NAME(aliasname)) -#elif defined(__ELF__) || defined(_AIX) +#elif defined(__ELF__) || defined(_AIX) || defined(__wasm__) #define _LIBUNWIND_WEAK_ALIAS(name, aliasname) \ extern "C" _LIBUNWIND_EXPORT __typeof(name) aliasname \ __attribute__((weak, alias(#name)));