1d4e04f7a7
On Wasm, it's not currently possibly to change which `personality` is attached to a given IR function. This is primarily because no matter what `personality` is attached, codegen creates a call to a `Unwind_CallPersonality` wrapper hard-coded to call c++abi's personality. In order to allow alternative personalities without introducing bloat at each personality call site, this PR adjusts the ABI of the personality on Wasm. `Unwind_CallPersonality` is moved to `libcxxabi` under the name `__gxx_wasm_personality_v0`, with the "real" personality code renamed `__gxx_personality_imp` and called by `__gxx_wasm_personality_v0` (after resetting the landing pad context). The signature of EH personalities on Wasm is now `int personality(void* exception_object)` (where the int return is `_Unwind_Reason_Code` and the `void*` is `_Unwind_Exception*`), and personalities are expected to `__wasm_lpad_context.selector = 0;`. Based on #175202
100 lines
3.7 KiB
C
100 lines
3.7 KiB
C
//===----------------------------------------------------------------------===//
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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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_LIBUNWIND_EXPORT thread_local struct _Unwind_LandingPadContext
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__wasm_lpad_context;
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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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// Define the `__cpp_exception` symbol which `__builtin_wasm_throw` above will
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// reference. This is defined here in `libunwind` as the single canonical
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// definition for this API and it's required for users to ensure that there's
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// only one copy of `libunwind` within a wasm module to ensure this is only
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// defined once and exactly once.
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__asm__(".globl __cpp_exception\n"
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#if defined(__wasm32__)
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".tagtype __cpp_exception i32\n"
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#elif defined(__wasm64__)
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".tagtype __cpp_exception i64\n"
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#else
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#error "Unsupported Wasm architecture"
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#endif
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"__cpp_exception:\n");
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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 a 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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