1 //! Implementation of panics backed by libgcc/libunwind (in some form).
3 //! For background on exception handling and stack unwinding please see
4 //! "Exception Handling in LLVM" (llvm.org/docs/ExceptionHandling.html) and
5 //! documents linked from it.
6 //! These are also good reads:
7 //! https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html
8 //! http://monoinfinito.wordpress.com/series/exception-handling-in-c/
9 //! http://www.airs.com/blog/index.php?s=exception+frames
11 //! ## A brief summary
13 //! Exception handling happens in two phases: a search phase and a cleanup
16 //! In both phases the unwinder walks stack frames from top to bottom using
17 //! information from the stack frame unwind sections of the current process's
18 //! modules ("module" here refers to an OS module, i.e., an executable or a
21 //! For each stack frame, it invokes the associated "personality routine", whose
22 //! address is also stored in the unwind info section.
24 //! In the search phase, the job of a personality routine is to examine
25 //! exception object being thrown, and to decide whether it should be caught at
26 //! that stack frame. Once the handler frame has been identified, cleanup phase
29 //! In the cleanup phase, the unwinder invokes each personality routine again.
30 //! This time it decides which (if any) cleanup code needs to be run for
31 //! the current stack frame. If so, the control is transferred to a special
32 //! branch in the function body, the "landing pad", which invokes destructors,
33 //! frees memory, etc. At the end of the landing pad, control is transferred
34 //! back to the unwinder and unwinding resumes.
36 //! Once stack has been unwound down to the handler frame level, unwinding stops
37 //! and the last personality routine transfers control to the catch block.
39 use alloc::boxed::Box;
42 use crate::dwarf::eh::{self, EHAction, EHContext};
43 use libc::{c_int, uintptr_t};
48 _uwe: uw::_Unwind_Exception,
49 cause: Box<dyn Any + Send>,
52 pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
53 let exception = Box::new(Exception {
54 _uwe: uw::_Unwind_Exception {
55 exception_class: rust_exception_class(),
57 private: [0; uw::unwinder_private_data_size],
61 let exception_param = Box::into_raw(exception) as *mut uw::_Unwind_Exception;
62 return uw::_Unwind_RaiseException(exception_param) as u32;
64 extern "C" fn exception_cleanup(
65 _unwind_code: uw::_Unwind_Reason_Code,
66 exception: *mut uw::_Unwind_Exception,
69 let _: Box<Exception> = Box::from_raw(exception as *mut Exception);
70 super::__rust_drop_panic();
75 pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
76 let exception = Box::from_raw(ptr as *mut Exception);
80 // Rust's exception class identifier. This is used by personality routines to
81 // determine whether the exception was thrown by their own runtime.
82 fn rust_exception_class() -> uw::_Unwind_Exception_Class {
83 // M O Z \0 R U S T -- vendor, language
87 // Register ids were lifted from LLVM's TargetLowering::getExceptionPointerRegister()
88 // and TargetLowering::getExceptionSelectorRegister() for each architecture,
89 // then mapped to DWARF register numbers via register definition tables
90 // (typically <arch>RegisterInfo.td, search for "DwarfRegNum").
91 // See also http://llvm.org/docs/WritingAnLLVMBackend.html#defining-a-register.
93 #[cfg(target_arch = "x86")]
94 const UNWIND_DATA_REG: (i32, i32) = (0, 2); // EAX, EDX
96 #[cfg(target_arch = "x86_64")]
97 const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX
99 #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
100 const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1 / X0, X1
102 #[cfg(any(target_arch = "mips", target_arch = "mips64"))]
103 const UNWIND_DATA_REG: (i32, i32) = (4, 5); // A0, A1
105 #[cfg(any(target_arch = "powerpc", target_arch = "powerpc64"))]
106 const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4 / X3, X4
108 #[cfg(target_arch = "s390x")]
109 const UNWIND_DATA_REG: (i32, i32) = (6, 7); // R6, R7
111 #[cfg(target_arch = "sparc64")]
112 const UNWIND_DATA_REG: (i32, i32) = (24, 25); // I0, I1
114 #[cfg(target_arch = "hexagon")]
115 const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1
117 #[cfg(target_arch = "riscv64")]
118 const UNWIND_DATA_REG: (i32, i32) = (10, 11); // x10, x11
120 // The following code is based on GCC's C and C++ personality routines. For reference, see:
121 // https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/libsupc++/eh_personality.cc
122 // https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
125 if #[cfg(all(target_arch = "arm", not(target_os = "ios"), not(target_os = "netbsd")))] {
126 // ARM EHABI personality routine.
127 // http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
129 // iOS uses the default routine instead since it uses SjLj unwinding.
130 #[lang = "eh_personality"]
131 unsafe extern "C" fn rust_eh_personality(state: uw::_Unwind_State,
132 exception_object: *mut uw::_Unwind_Exception,
133 context: *mut uw::_Unwind_Context)
134 -> uw::_Unwind_Reason_Code {
135 let state = state as c_int;
136 let action = state & uw::_US_ACTION_MASK as c_int;
137 let search_phase = if action == uw::_US_VIRTUAL_UNWIND_FRAME as c_int {
138 // Backtraces on ARM will call the personality routine with
139 // state == _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND. In those cases
140 // we want to continue unwinding the stack, otherwise all our backtraces
141 // would end at __rust_try
142 if state & uw::_US_FORCE_UNWIND as c_int != 0 {
143 return continue_unwind(exception_object, context);
146 } else if action == uw::_US_UNWIND_FRAME_STARTING as c_int {
148 } else if action == uw::_US_UNWIND_FRAME_RESUME as c_int {
149 return continue_unwind(exception_object, context);
151 return uw::_URC_FAILURE;
154 // The DWARF unwinder assumes that _Unwind_Context holds things like the function
155 // and LSDA pointers, however ARM EHABI places them into the exception object.
156 // To preserve signatures of functions like _Unwind_GetLanguageSpecificData(), which
157 // take only the context pointer, GCC personality routines stash a pointer to
158 // exception_object in the context, using location reserved for ARM's
159 // "scratch register" (r12).
160 uw::_Unwind_SetGR(context,
161 uw::UNWIND_POINTER_REG,
162 exception_object as uw::_Unwind_Ptr);
163 // ...A more principled approach would be to provide the full definition of ARM's
164 // _Unwind_Context in our libunwind bindings and fetch the required data from there
165 // directly, bypassing DWARF compatibility functions.
167 let exception_class = (*exception_object).exception_class;
168 let foreign_exception = exception_class != rust_exception_class();
169 let eh_action = match find_eh_action(context, foreign_exception) {
170 Ok(action) => action,
171 Err(_) => return uw::_URC_FAILURE,
176 EHAction::Cleanup(_) => return continue_unwind(exception_object, context),
177 EHAction::Catch(_) => {
178 // EHABI requires the personality routine to update the
179 // SP value in the barrier cache of the exception object.
180 (*exception_object).private[5] =
181 uw::_Unwind_GetGR(context, uw::UNWIND_SP_REG);
182 return uw::_URC_HANDLER_FOUND;
184 EHAction::Terminate => return uw::_URC_FAILURE,
188 EHAction::None => return continue_unwind(exception_object, context),
189 EHAction::Cleanup(lpad) |
190 EHAction::Catch(lpad) => {
191 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0,
192 exception_object as uintptr_t);
193 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
194 uw::_Unwind_SetIP(context, lpad);
195 return uw::_URC_INSTALL_CONTEXT;
197 EHAction::Terminate => return uw::_URC_FAILURE,
201 // On ARM EHABI the personality routine is responsible for actually
202 // unwinding a single stack frame before returning (ARM EHABI Sec. 6.1).
203 unsafe fn continue_unwind(exception_object: *mut uw::_Unwind_Exception,
204 context: *mut uw::_Unwind_Context)
205 -> uw::_Unwind_Reason_Code {
206 if __gnu_unwind_frame(exception_object, context) == uw::_URC_NO_REASON {
207 uw::_URC_CONTINUE_UNWIND
214 fn __gnu_unwind_frame(exception_object: *mut uw::_Unwind_Exception,
215 context: *mut uw::_Unwind_Context)
216 -> uw::_Unwind_Reason_Code;
220 // Default personality routine, which is used directly on most targets
221 // and indirectly on Windows x86_64 via SEH.
222 unsafe extern "C" fn rust_eh_personality_impl(version: c_int,
223 actions: uw::_Unwind_Action,
224 exception_class: uw::_Unwind_Exception_Class,
225 exception_object: *mut uw::_Unwind_Exception,
226 context: *mut uw::_Unwind_Context)
227 -> uw::_Unwind_Reason_Code {
229 return uw::_URC_FATAL_PHASE1_ERROR;
231 let foreign_exception = exception_class != rust_exception_class();
232 let eh_action = match find_eh_action(context, foreign_exception) {
233 Ok(action) => action,
234 Err(_) => return uw::_URC_FATAL_PHASE1_ERROR,
236 if actions as i32 & uw::_UA_SEARCH_PHASE as i32 != 0 {
239 EHAction::Cleanup(_) => uw::_URC_CONTINUE_UNWIND,
240 EHAction::Catch(_) => uw::_URC_HANDLER_FOUND,
241 EHAction::Terminate => uw::_URC_FATAL_PHASE1_ERROR,
245 EHAction::None => uw::_URC_CONTINUE_UNWIND,
246 EHAction::Cleanup(lpad) |
247 EHAction::Catch(lpad) => {
248 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0,
249 exception_object as uintptr_t);
250 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
251 uw::_Unwind_SetIP(context, lpad);
252 uw::_URC_INSTALL_CONTEXT
254 EHAction::Terminate => uw::_URC_FATAL_PHASE2_ERROR,
260 if #[cfg(all(windows, target_arch = "x86_64", target_env = "gnu"))] {
261 // On x86_64 MinGW targets, the unwinding mechanism is SEH however the unwind
262 // handler data (aka LSDA) uses GCC-compatible encoding.
263 #[lang = "eh_personality"]
264 #[allow(nonstandard_style)]
265 unsafe extern "C" fn rust_eh_personality(exceptionRecord: *mut uw::EXCEPTION_RECORD,
266 establisherFrame: uw::LPVOID,
267 contextRecord: *mut uw::CONTEXT,
268 dispatcherContext: *mut uw::DISPATCHER_CONTEXT)
269 -> uw::EXCEPTION_DISPOSITION {
270 uw::_GCC_specific_handler(exceptionRecord,
274 rust_eh_personality_impl)
277 // The personality routine for most of our targets.
278 #[lang = "eh_personality"]
279 unsafe extern "C" fn rust_eh_personality(version: c_int,
280 actions: uw::_Unwind_Action,
281 exception_class: uw::_Unwind_Exception_Class,
282 exception_object: *mut uw::_Unwind_Exception,
283 context: *mut uw::_Unwind_Context)
284 -> uw::_Unwind_Reason_Code {
285 rust_eh_personality_impl(version,
296 unsafe fn find_eh_action(
297 context: *mut uw::_Unwind_Context,
298 foreign_exception: bool,
299 ) -> Result<EHAction, ()> {
300 let lsda = uw::_Unwind_GetLanguageSpecificData(context) as *const u8;
301 let mut ip_before_instr: c_int = 0;
302 let ip = uw::_Unwind_GetIPInfo(context, &mut ip_before_instr);
303 let eh_context = EHContext {
304 // The return address points 1 byte past the call instruction,
305 // which could be in the next IP range in LSDA range table.
306 ip: if ip_before_instr != 0 { ip } else { ip - 1 },
307 func_start: uw::_Unwind_GetRegionStart(context),
308 get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
309 get_data_start: &|| uw::_Unwind_GetDataRelBase(context),
311 eh::find_eh_action(lsda, &eh_context, foreign_exception)
316 target_os = "windows",
317 any(target_arch = "x86", target_arch = "x86_64"),
320 #[lang = "eh_unwind_resume"]
322 unsafe extern "C" fn rust_eh_unwind_resume(panic_ctx: *mut u8) -> ! {
323 uw::_Unwind_Resume(panic_ctx as *mut uw::_Unwind_Exception);
326 // Frame unwind info registration
328 // Each module's image contains a frame unwind info section (usually
329 // ".eh_frame"). When a module is loaded/unloaded into the process, the
330 // unwinder must be informed about the location of this section in memory. The
331 // methods of achieving that vary by the platform. On some (e.g., Linux), the
332 // unwinder can discover unwind info sections on its own (by dynamically
333 // enumerating currently loaded modules via the dl_iterate_phdr() API and
334 // finding their ".eh_frame" sections); Others, like Windows, require modules
335 // to actively register their unwind info sections via unwinder API.
337 // This module defines two symbols which are referenced and called from
338 // rsbegin.rs to register our information with the GCC runtime. The
339 // implementation of stack unwinding is (for now) deferred to libgcc_eh, however
340 // Rust crates use these Rust-specific entry points to avoid potential clashes
341 // with any GCC runtime.
342 #[cfg(all(target_os = "windows", target_arch = "x86", target_env = "gnu"))]
343 pub mod eh_frame_registry {
345 fn __register_frame_info(eh_frame_begin: *const u8, object: *mut u8);
346 fn __deregister_frame_info(eh_frame_begin: *const u8, object: *mut u8);
349 #[rustc_std_internal_symbol]
350 pub unsafe extern "C" fn rust_eh_register_frames(eh_frame_begin: *const u8, object: *mut u8) {
351 __register_frame_info(eh_frame_begin, object);
354 #[rustc_std_internal_symbol]
355 pub unsafe extern "C" fn rust_eh_unregister_frames(eh_frame_begin: *const u8, object: *mut u8) {
356 __deregister_frame_info(eh_frame_begin, object);