diff options
| -rw-r--r-- | library/panic_unwind/src/seh.rs | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/library/panic_unwind/src/seh.rs b/library/panic_unwind/src/seh.rs index 003ac4f0cd3..668e988abff 100644 --- a/library/panic_unwind/src/seh.rs +++ b/library/panic_unwind/src/seh.rs @@ -61,6 +61,7 @@ struct Exception { // and its destructor is executed by the C++ runtime. When we take the Box // out of the exception, we need to leave the exception in a valid state // for its destructor to run without double-dropping the Box. + // We also construct this as None for copies of the exception. data: Option<Box<dyn Any + Send>>, } @@ -264,7 +265,11 @@ static mut TYPE_DESCRIPTOR: _TypeDescriptor = _TypeDescriptor { // runtime under a try/catch block and the panic that we generate here will be // used as the result of the exception copy. This is used by the C++ runtime to // support capturing exceptions with std::exception_ptr, which we can't support -// because Box<dyn Any> isn't clonable. +// because Box<dyn Any> isn't clonable. Thus we throw an exception without data, +// which the C++ runtime will attempt to copy, which will once again fail, and +// a std::bad_exception instance ends up in the std::exception_ptr instance. +// The lack of data doesn't matter because the exception will never be rethrown +// - it is purely used to signal to the C++ runtime that copying failed. macro_rules! define_cleanup { ($abi:tt $abi2:tt) => { unsafe extern $abi fn exception_cleanup(e: *mut Exception) { @@ -278,7 +283,9 @@ macro_rules! define_cleanup { unsafe extern $abi2 fn exception_copy( _dest: *mut Exception, _src: *mut Exception ) -> *mut Exception { - panic!("Rust panics cannot be copied"); + unsafe { + throw_exception(None); + } } } } @@ -291,6 +298,10 @@ cfg_if::cfg_if! { } pub(crate) unsafe fn panic(data: Box<dyn Any + Send>) -> u32 { + unsafe { throw_exception(Some(data)) } +} + +unsafe fn throw_exception(data: Option<Box<dyn Any + Send>>) -> ! { use core::intrinsics::{AtomicOrdering, atomic_store}; // _CxxThrowException executes entirely on this stack frame, so there's no @@ -300,8 +311,7 @@ pub(crate) unsafe fn panic(data: Box<dyn Any + Send>) -> u32 { // The ManuallyDrop is needed here since we don't want Exception to be // dropped when unwinding. Instead it will be dropped by exception_cleanup // which is invoked by the C++ runtime. - let mut exception = - ManuallyDrop::new(Exception { canary: (&raw const TYPE_DESCRIPTOR), data: Some(data) }); + let mut exception = ManuallyDrop::new(Exception { canary: (&raw const TYPE_DESCRIPTOR), data }); let throw_ptr = (&raw mut exception) as *mut _; // This... may seems surprising, and justifiably so. On 32-bit MSVC the |