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//! A shim for libunwind implemented in terms of the native wasm `throw` instruction.
#![allow(nonstandard_style)]
#[repr(C)]
#[derive(Debug, Copy, Clone, PartialEq)]
pub enum _Unwind_Reason_Code {
_URC_NO_REASON = 0,
_URC_FOREIGN_EXCEPTION_CAUGHT = 1,
_URC_FATAL_PHASE2_ERROR = 2,
_URC_FATAL_PHASE1_ERROR = 3,
_URC_NORMAL_STOP = 4,
_URC_END_OF_STACK = 5,
_URC_HANDLER_FOUND = 6,
_URC_INSTALL_CONTEXT = 7,
_URC_CONTINUE_UNWIND = 8,
_URC_FAILURE = 9, // used only by ARM EHABI
}
pub use _Unwind_Reason_Code::*;
pub type _Unwind_Exception_Class = u64;
pub type _Unwind_Word = *const u8;
pub const unwinder_private_data_size: usize = 2;
#[repr(C)]
pub struct _Unwind_Exception {
pub exception_class: _Unwind_Exception_Class,
pub exception_cleanup: _Unwind_Exception_Cleanup_Fn,
pub private: [_Unwind_Word; unwinder_private_data_size],
}
pub type _Unwind_Exception_Cleanup_Fn =
Option<extern "C" fn(unwind_code: _Unwind_Reason_Code, exception: *mut _Unwind_Exception)>;
pub unsafe fn _Unwind_DeleteException(exception: *mut _Unwind_Exception) {
if let Some(exception_cleanup) = unsafe { (*exception).exception_cleanup } {
exception_cleanup(_URC_FOREIGN_EXCEPTION_CAUGHT, exception);
}
}
pub unsafe fn _Unwind_RaiseException(exception: *mut _Unwind_Exception) -> _Unwind_Reason_Code {
// The wasm `throw` instruction takes a "tag", which differentiates certain
// types of exceptions from others. LLVM currently just identifies these
// via integers, with 0 corresponding to C++ exceptions and 1 to C setjmp()/longjmp().
// Ideally, we'd be able to choose something unique for Rust, but for now,
// we pretend to be C++ and implement the Itanium exception-handling ABI.
cfg_select! {
// panic=abort is default for wasm targets. Because an unknown instruction is a load-time
// error on wasm, instead of a runtime error like on traditional architectures, we never
// want to codegen a `throw` instruction, as that would break users using runtimes that
// don't yet support exceptions. The only time this first branch would be selected is if
// the user explicitly opts in to wasm exceptions, via -Zbuild-std with -Cpanic=unwind.
panic = "unwind" => {
// corresponds with llvm::WebAssembly::Tag::CPP_EXCEPTION
// in llvm-project/llvm/include/llvm/CodeGen/WasmEHFuncInfo.h
const CPP_EXCEPTION_TAG: i32 = 0;
core::arch::wasm::throw::<CPP_EXCEPTION_TAG>(exception.cast())
}
_ => {
let _ = exception;
core::arch::wasm::unreachable()
}
}
}
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