src/libpanic_unwind/gcc.rs - third_party/rust - Git at Google

 //! 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);
     }
 }
	//! 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);
	}
	}