| //! 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: |
| //! http://mentorembedded.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. |
| |
| #![allow(private_no_mangle_fns)] |
| |
| use core::any::Any; |
| use core::ptr; |
| use alloc::boxed::Box; |
| |
| use unwind as uw; |
| use libc::{c_int, uintptr_t}; |
| use crate::dwarf::eh::{self, EHContext, EHAction}; |
| |
| #[repr(C)] |
| struct Exception { |
| _uwe: uw::_Unwind_Exception, |
| cause: Option<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: Some(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); |
| } |
| } |
| } |
| |
| pub fn payload() -> *mut u8 { |
| ptr::null_mut() |
| } |
| |
| pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> { |
| let my_ep = ptr as *mut Exception; |
| let cause = (*my_ep).cause.take(); |
| uw::_Unwind_DeleteException(ptr as *mut _); |
| cause.unwrap() |
| } |
| |
| // 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 |
| |
| #[cfg(any(target_arch = "arm", target_arch = "aarch64"))] |
| const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1 / X0, X1 |
| |
| #[cfg(any(target_arch = "mips", target_arch = "mips64"))] |
| const UNWIND_DATA_REG: (i32, i32) = (4, 5); // A0, A1 |
| |
| #[cfg(any(target_arch = "powerpc", target_arch = "powerpc64"))] |
| const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4 / X3, X4 |
| |
| #[cfg(target_arch = "s390x")] |
| const UNWIND_DATA_REG: (i32, i32) = (6, 7); // R6, R7 |
| |
| #[cfg(target_arch = "sparc64")] |
| const UNWIND_DATA_REG: (i32, i32) = (24, 25); // I0, I1 |
| |
| #[cfg(target_arch = "hexagon")] |
| const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1 |
| |
| // 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 |
| |
| // The personality routine for most of our targets, except ARM, which has a slightly different ABI |
| // (however, iOS goes here as it uses SjLj unwinding). Also, the 64-bit Windows implementation |
| // lives in seh64_gnu.rs |
| #[cfg(all(any(target_os = "ios", target_os = "netbsd", not(target_arch = "arm"))))] |
| #[lang = "eh_personality"] |
| #[no_mangle] |
| #[allow(unused)] |
| 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 { |
| if version != 1 { |
| return uw::_URC_FATAL_PHASE1_ERROR; |
| } |
| let eh_action = match find_eh_action(context) { |
| 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(_) => return uw::_URC_CONTINUE_UNWIND, |
| EHAction::Catch(_) => return uw::_URC_HANDLER_FOUND, |
| EHAction::Terminate => return uw::_URC_FATAL_PHASE1_ERROR, |
| } |
| } else { |
| match eh_action { |
| EHAction::None => return 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); |
| return uw::_URC_INSTALL_CONTEXT; |
| } |
| EHAction::Terminate => return uw::_URC_FATAL_PHASE2_ERROR, |
| } |
| } |
| } |
| |
| // ARM EHABI personality routine. |
| // http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf |
| #[cfg(all(target_arch = "arm", not(target_os = "ios"), not(target_os = "netbsd")))] |
| #[lang = "eh_personality"] |
| #[no_mangle] |
| unsafe extern "C" fn rust_eh_personality(state: uw::_Unwind_State, |
| exception_object: *mut uw::_Unwind_Exception, |
| context: *mut uw::_Unwind_Context) |
| -> uw::_Unwind_Reason_Code { |
| let state = state as c_int; |
| let action = state & uw::_US_ACTION_MASK as c_int; |
| let search_phase = if action == uw::_US_VIRTUAL_UNWIND_FRAME as c_int { |
| // Backtraces on ARM will call the personality routine with |
| // state == _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND. In those cases |
| // we want to continue unwinding the stack, otherwise all our backtraces |
| // would end at __rust_try |
| if state & uw::_US_FORCE_UNWIND as c_int != 0 { |
| return continue_unwind(exception_object, context); |
| } |
| true |
| } else if action == uw::_US_UNWIND_FRAME_STARTING as c_int { |
| false |
| } else if action == uw::_US_UNWIND_FRAME_RESUME as c_int { |
| return continue_unwind(exception_object, context); |
| } else { |
| return uw::_URC_FAILURE; |
| }; |
| |
| // The DWARF unwinder assumes that _Unwind_Context holds things like the function |
| // and LSDA pointers, however ARM EHABI places them into the exception object. |
| // To preserve signatures of functions like _Unwind_GetLanguageSpecificData(), which |
| // take only the context pointer, GCC personality routines stash a pointer to exception_object |
| // in the context, using location reserved for ARM's "scratch register" (r12). |
| uw::_Unwind_SetGR(context, |
| uw::UNWIND_POINTER_REG, |
| exception_object as uw::_Unwind_Ptr); |
| // ...A more principled approach would be to provide the full definition of ARM's |
| // _Unwind_Context in our libunwind bindings and fetch the required data from there directly, |
| // bypassing DWARF compatibility functions. |
| |
| let eh_action = match find_eh_action(context) { |
| Ok(action) => action, |
| Err(_) => return uw::_URC_FAILURE, |
| }; |
| if search_phase { |
| match eh_action { |
| EHAction::None | |
| EHAction::Cleanup(_) => return continue_unwind(exception_object, context), |
| EHAction::Catch(_) => return uw::_URC_HANDLER_FOUND, |
| EHAction::Terminate => return uw::_URC_FAILURE, |
| } |
| } else { |
| match eh_action { |
| EHAction::None => return continue_unwind(exception_object, context), |
| 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); |
| return uw::_URC_INSTALL_CONTEXT; |
| } |
| EHAction::Terminate => return uw::_URC_FAILURE, |
| } |
| } |
| |
| // On ARM EHABI the personality routine is responsible for actually |
| // unwinding a single stack frame before returning (ARM EHABI Sec. 6.1). |
| unsafe fn continue_unwind(exception_object: *mut uw::_Unwind_Exception, |
| context: *mut uw::_Unwind_Context) |
| -> uw::_Unwind_Reason_Code { |
| if __gnu_unwind_frame(exception_object, context) == uw::_URC_NO_REASON { |
| uw::_URC_CONTINUE_UNWIND |
| } else { |
| uw::_URC_FAILURE |
| } |
| } |
| // defined in libgcc |
| extern "C" { |
| fn __gnu_unwind_frame(exception_object: *mut uw::_Unwind_Exception, |
| context: *mut uw::_Unwind_Context) |
| -> uw::_Unwind_Reason_Code; |
| } |
| } |
| |
| unsafe fn find_eh_action(context: *mut uw::_Unwind_Context) |
| -> 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) |
| } |
| |
| // See docs in the `unwind` module. |
| #[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))] |
| #[lang = "eh_unwind_resume"] |
| #[unwind(allowed)] |
| unsafe extern "C" fn rust_eh_unwind_resume(panic_ctx: *mut u8) -> ! { |
| uw::_Unwind_Resume(panic_ctx as *mut uw::_Unwind_Exception); |
| } |
| |
| // Frame unwind info registration |
| // |
| // Each module's image contains a frame unwind info section (usually |
| // ".eh_frame"). When a module is loaded/unloaded into the process, the |
| // unwinder must be informed about the location of this section in memory. The |
| // methods of achieving that vary by the platform. On some (e.g., Linux), the |
| // unwinder can discover unwind info sections on its own (by dynamically |
| // enumerating currently loaded modules via the dl_iterate_phdr() API and |
| // finding their ".eh_frame" sections); Others, like Windows, require modules |
| // to actively register their unwind info sections via unwinder API. |
| // |
| // This module defines two symbols which are referenced and called from |
| // rsbegin.rs to register our information with the GCC runtime. The |
| // implementation of stack unwinding is (for now) deferred to libgcc_eh, however |
| // Rust crates use these Rust-specific entry points to avoid potential clashes |
| // with any GCC runtime. |
| #[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))] |
| pub mod eh_frame_registry { |
| extern "C" { |
| fn __register_frame_info(eh_frame_begin: *const u8, object: *mut u8); |
| fn __deregister_frame_info(eh_frame_begin: *const u8, object: *mut u8); |
| } |
| |
| #[no_mangle] |
| pub unsafe extern "C" fn rust_eh_register_frames(eh_frame_begin: *const u8, object: *mut u8) { |
| __register_frame_info(eh_frame_begin, object); |
| } |
| |
| #[no_mangle] |
| pub unsafe extern "C" fn rust_eh_unregister_frames(eh_frame_begin: *const u8, |
| object: *mut u8) { |
| __deregister_frame_info(eh_frame_begin, object); |
| } |
| } |