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//===----------------------------------------------------------------------===//
//
// 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 <stdbool.h>
#include "config.h"
#ifdef __USING_WASM_EXCEPTIONS__
#include "unwind.h"
#include <threads.h>
_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 __attribute__((unused)),
uintptr_t value __attribute__((unused))) {}
/// 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 __attribute__((unused))) {
return 0;
}
#endif // defined(__USING_WASM_EXCEPTIONS__)
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