| //! Implementation of panics backed by libgcc/libunwind (in some form). |
| //! |
| //! For background on exception handling and stack unwinding please see |
| //! "Exception Handling in LLVM" (llvm.org/docs/ExceptionHandling.html) and |
| //! documents linked from it. |
| //! These are also good reads: |
| //! https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html |
| //! http://monoinfinito.wordpress.com/series/exception-handling-in-c/ |
| //! http://www.airs.com/blog/index.php?s=exception+frames |
| //! |
| //! ## A brief summary |
| //! |
| //! Exception handling happens in two phases: a search phase and a cleanup |
| //! phase. |
| //! |
| //! In both phases the unwinder walks stack frames from top to bottom using |
| //! information from the stack frame unwind sections of the current process's |
| //! modules ("module" here refers to an OS module, i.e., an executable or a |
| //! dynamic library). |
| //! |
| //! For each stack frame, it invokes the associated "personality routine", whose |
| //! address is also stored in the unwind info section. |
| //! |
| //! In the search phase, the job of a personality routine is to examine |
| //! exception object being thrown, and to decide whether it should be caught at |
| //! that stack frame. Once the handler frame has been identified, cleanup phase |
| //! begins. |
| //! |
| //! In the cleanup phase, the unwinder invokes each personality routine again. |
| //! This time it decides which (if any) cleanup code needs to be run for |
| //! the current stack frame. If so, the control is transferred to a special |
| //! branch in the function body, the "landing pad", which invokes destructors, |
| //! frees memory, etc. At the end of the landing pad, control is transferred |
| //! back to the unwinder and unwinding resumes. |
| //! |
| //! Once stack has been unwound down to the handler frame level, unwinding stops |
| //! and the last personality routine transfers control to the catch block. |
| //! |
| //! ## `eh_personality` and `eh_unwind_resume` |
| //! |
| //! These language items are used by the compiler when generating unwind info. |
| //! The first one is the personality routine described above. The second one |
| //! allows compilation target to customize the process of resuming unwind at the |
| //! end of the landing pads. `eh_unwind_resume` is used only if |
| //! `custom_unwind_resume` flag in the target options is set. |
| |
| use alloc::boxed::Box; |
| use core::any::Any; |
| |
| use crate::dwarf::eh::{self, EHAction, EHContext}; |
| use sgx_libc::{c_int, uintptr_t}; |
| use sgx_unwind as uw; |
| |
| #[repr(C)] |
| struct Exception { |
| _uwe: uw::_Unwind_Exception, |
| cause: Box<dyn Any + Send>, |
| } |
| |
| pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 { |
| let exception = Box::new(Exception { |
| _uwe: uw::_Unwind_Exception { |
| exception_class: rust_exception_class(), |
| exception_cleanup, |
| private: [0; uw::unwinder_private_data_size], |
| }, |
| cause: data, |
| }); |
| let exception_param = Box::into_raw(exception) as *mut uw::_Unwind_Exception; |
| return uw::_Unwind_RaiseException(exception_param) as u32; |
| |
| extern "C" fn exception_cleanup( |
| _unwind_code: uw::_Unwind_Reason_Code, |
| exception: *mut uw::_Unwind_Exception, |
| ) { |
| unsafe { |
| let _: Box<Exception> = Box::from_raw(exception as *mut Exception); |
| super::__rust_drop_panic(); |
| } |
| } |
| } |
| |
| pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> { |
| let exception = Box::from_raw(ptr as *mut Exception); |
| exception.cause |
| } |
| |
| // Rust's exception class identifier. This is used by personality routines to |
| // determine whether the exception was thrown by their own runtime. |
| fn rust_exception_class() -> uw::_Unwind_Exception_Class { |
| // M O Z \0 R U S T -- vendor, language |
| 0x4d4f5a_00_52555354 |
| } |
| |
| // Register ids were lifted from LLVM's TargetLowering::getExceptionPointerRegister() |
| // and TargetLowering::getExceptionSelectorRegister() for each architecture, |
| // then mapped to DWARF register numbers via register definition tables |
| // (typically <arch>RegisterInfo.td, search for "DwarfRegNum"). |
| // See also http://llvm.org/docs/WritingAnLLVMBackend.html#defining-a-register. |
| |
| #[cfg(target_arch = "x86")] |
| const UNWIND_DATA_REG: (i32, i32) = (0, 2); // EAX, EDX |
| |
| #[cfg(target_arch = "x86_64")] |
| const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX |
| |
| // The following code is based on GCC's C and C++ personality routines. For reference, see: |
| // https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/libsupc++/eh_personality.cc |
| // https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c |
| |
| unsafe extern "C" fn rust_eh_personality_impl( |
| version: c_int, |
| actions: uw::_Unwind_Action, |
| exception_class: uw::_Unwind_Exception_Class, |
| exception_object: *mut uw::_Unwind_Exception, |
| context: *mut uw::_Unwind_Context) |
| -> uw::_Unwind_Reason_Code { |
| if version != 1 { |
| return uw::_URC_FATAL_PHASE1_ERROR; |
| } |
| let foreign_exception = exception_class != rust_exception_class(); |
| let eh_action = match find_eh_action(context, foreign_exception) { |
| Ok(action) => action, |
| Err(_) => return uw::_URC_FATAL_PHASE1_ERROR, |
| }; |
| if actions as i32 & uw::_UA_SEARCH_PHASE as i32 != 0 { |
| match eh_action { |
| EHAction::None | |
| EHAction::Cleanup(_) => uw::_URC_CONTINUE_UNWIND, |
| EHAction::Catch(_) => uw::_URC_HANDLER_FOUND, |
| EHAction::Terminate => uw::_URC_FATAL_PHASE1_ERROR, |
| } |
| } else { |
| match eh_action { |
| EHAction::None => uw::_URC_CONTINUE_UNWIND, |
| EHAction::Cleanup(lpad) | |
| EHAction::Catch(lpad) => { |
| uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0, |
| exception_object as uintptr_t); |
| uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0); |
| uw::_Unwind_SetIP(context, lpad); |
| uw::_URC_INSTALL_CONTEXT |
| } |
| EHAction::Terminate => uw::_URC_FATAL_PHASE2_ERROR, |
| } |
| } |
| } |
| |
| #[lang = "eh_personality"] |
| unsafe extern "C" fn rust_eh_personality( |
| version: c_int, |
| actions: uw::_Unwind_Action, |
| exception_class: uw::_Unwind_Exception_Class, |
| exception_object: *mut uw::_Unwind_Exception, |
| context: *mut uw::_Unwind_Context) |
| -> uw::_Unwind_Reason_Code { |
| rust_eh_personality_impl( |
| version, |
| actions, |
| exception_class, |
| exception_object, |
| context) |
| } |
| |
| unsafe fn find_eh_action( |
| context: *mut uw::_Unwind_Context, |
| foreign_exception: bool, |
| ) -> Result<EHAction, ()> { |
| let lsda = uw::_Unwind_GetLanguageSpecificData(context) as *const u8; |
| let mut ip_before_instr: c_int = 0; |
| let ip = uw::_Unwind_GetIPInfo(context, &mut ip_before_instr); |
| let eh_context = EHContext { |
| // The return address points 1 byte past the call instruction, |
| // which could be in the next IP range in LSDA range table. |
| ip: if ip_before_instr != 0 { ip } else { ip - 1 }, |
| func_start: uw::_Unwind_GetRegionStart(context), |
| get_text_start: &|| uw::_Unwind_GetTextRelBase(context), |
| get_data_start: &|| uw::_Unwind_GetDataRelBase(context), |
| }; |
| eh::find_eh_action(lsda, &eh_context, foreign_exception) |
| } |