llvm-project

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