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 //! http://mentorembedded.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 //! ## `eh_personality` and `eh_unwind_resume`
41 //! These language items are used by the compiler when generating unwind info.
42 //! The first one is the personality routine described above. The second one
43 //! allows compilation target to customize the process of resuming unwind at the
44 //! end of the landing pads. `eh_unwind_resume` is used only if
45 //! `custom_unwind_resume` flag in the target options is set.
47 #![allow(private_no_mangle_fns)]
51 use alloc::boxed::Box;
54 use libc::{c_int, uintptr_t};
55 use crate::dwarf::eh::{self, EHContext, EHAction};
59 _uwe: uw::_Unwind_Exception,
60 cause: Option<Box<dyn Any + Send>>,
63 pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
64 let exception = Box::new(Exception {
65 _uwe: uw::_Unwind_Exception {
66 exception_class: rust_exception_class(),
68 private: [0; uw::unwinder_private_data_size],
72 let exception_param = Box::into_raw(exception) as *mut uw::_Unwind_Exception;
73 return uw::_Unwind_RaiseException(exception_param) as u32;
75 extern "C" fn exception_cleanup(_unwind_code: uw::_Unwind_Reason_Code,
76 exception: *mut uw::_Unwind_Exception) {
78 let _: Box<Exception> = Box::from_raw(exception as *mut Exception);
83 pub fn payload() -> *mut u8 {
87 pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
88 let my_ep = ptr as *mut Exception;
89 let cause = (*my_ep).cause.take();
90 uw::_Unwind_DeleteException(ptr as *mut _);
94 // Rust's exception class identifier. This is used by personality routines to
95 // determine whether the exception was thrown by their own runtime.
96 fn rust_exception_class() -> uw::_Unwind_Exception_Class {
97 // M O Z \0 R U S T -- vendor, language
102 // Register ids were lifted from LLVM's TargetLowering::getExceptionPointerRegister()
103 // and TargetLowering::getExceptionSelectorRegister() for each architecture,
104 // then mapped to DWARF register numbers via register definition tables
105 // (typically <arch>RegisterInfo.td, search for "DwarfRegNum").
106 // See also http://llvm.org/docs/WritingAnLLVMBackend.html#defining-a-register.
108 #[cfg(target_arch = "x86")]
109 const UNWIND_DATA_REG: (i32, i32) = (0, 2); // EAX, EDX
111 #[cfg(target_arch = "x86_64")]
112 const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX
114 #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
115 const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1 / X0, X1
117 #[cfg(any(target_arch = "mips", target_arch = "mips64"))]
118 const UNWIND_DATA_REG: (i32, i32) = (4, 5); // A0, A1
120 #[cfg(any(target_arch = "powerpc", target_arch = "powerpc64"))]
121 const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4 / X3, X4
123 #[cfg(target_arch = "s390x")]
124 const UNWIND_DATA_REG: (i32, i32) = (6, 7); // R6, R7
126 #[cfg(target_arch = "sparc64")]
127 const UNWIND_DATA_REG: (i32, i32) = (24, 25); // I0, I1
129 // The following code is based on GCC's C and C++ personality routines. For reference, see:
130 // https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/libsupc++/eh_personality.cc
131 // https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
133 // The personality routine for most of our targets, except ARM, which has a slightly different ABI
134 // (however, iOS goes here as it uses SjLj unwinding). Also, the 64-bit Windows implementation
135 // lives in seh64_gnu.rs
136 #[cfg(all(any(target_os = "ios", target_os = "netbsd", not(target_arch = "arm"))))]
137 #[lang = "eh_personality"]
140 unsafe extern "C" fn rust_eh_personality(version: c_int,
141 actions: uw::_Unwind_Action,
142 exception_class: uw::_Unwind_Exception_Class,
143 exception_object: *mut uw::_Unwind_Exception,
144 context: *mut uw::_Unwind_Context)
145 -> uw::_Unwind_Reason_Code {
147 return uw::_URC_FATAL_PHASE1_ERROR;
149 let eh_action = match find_eh_action(context) {
150 Ok(action) => action,
151 Err(_) => return uw::_URC_FATAL_PHASE1_ERROR,
153 if actions as i32 & uw::_UA_SEARCH_PHASE as i32 != 0 {
156 EHAction::Cleanup(_) => return uw::_URC_CONTINUE_UNWIND,
157 EHAction::Catch(_) => return uw::_URC_HANDLER_FOUND,
158 EHAction::Terminate => return uw::_URC_FATAL_PHASE1_ERROR,
162 EHAction::None => return uw::_URC_CONTINUE_UNWIND,
163 EHAction::Cleanup(lpad) |
164 EHAction::Catch(lpad) => {
165 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0, exception_object as uintptr_t);
166 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
167 uw::_Unwind_SetIP(context, lpad);
168 return uw::_URC_INSTALL_CONTEXT;
170 EHAction::Terminate => return uw::_URC_FATAL_PHASE2_ERROR,
175 // ARM EHABI personality routine.
176 // http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
177 #[cfg(all(target_arch = "arm", not(target_os = "ios"), not(target_os = "netbsd")))]
178 #[lang = "eh_personality"]
180 unsafe extern "C" fn rust_eh_personality(state: uw::_Unwind_State,
181 exception_object: *mut uw::_Unwind_Exception,
182 context: *mut uw::_Unwind_Context)
183 -> uw::_Unwind_Reason_Code {
184 let state = state as c_int;
185 let action = state & uw::_US_ACTION_MASK as c_int;
186 let search_phase = if action == uw::_US_VIRTUAL_UNWIND_FRAME as c_int {
187 // Backtraces on ARM will call the personality routine with
188 // state == _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND. In those cases
189 // we want to continue unwinding the stack, otherwise all our backtraces
190 // would end at __rust_try
191 if state & uw::_US_FORCE_UNWIND as c_int != 0 {
192 return continue_unwind(exception_object, context);
195 } else if action == uw::_US_UNWIND_FRAME_STARTING as c_int {
197 } else if action == uw::_US_UNWIND_FRAME_RESUME as c_int {
198 return continue_unwind(exception_object, context);
200 return uw::_URC_FAILURE;
203 // The DWARF unwinder assumes that _Unwind_Context holds things like the function
204 // and LSDA pointers, however ARM EHABI places them into the exception object.
205 // To preserve signatures of functions like _Unwind_GetLanguageSpecificData(), which
206 // take only the context pointer, GCC personality routines stash a pointer to exception_object
207 // in the context, using location reserved for ARM's "scratch register" (r12).
208 uw::_Unwind_SetGR(context,
209 uw::UNWIND_POINTER_REG,
210 exception_object as uw::_Unwind_Ptr);
211 // ...A more principled approach would be to provide the full definition of ARM's
212 // _Unwind_Context in our libunwind bindings and fetch the required data from there directly,
213 // bypassing DWARF compatibility functions.
215 let eh_action = match find_eh_action(context) {
216 Ok(action) => action,
217 Err(_) => return uw::_URC_FAILURE,
222 EHAction::Cleanup(_) => return continue_unwind(exception_object, context),
223 EHAction::Catch(_) => return uw::_URC_HANDLER_FOUND,
224 EHAction::Terminate => return uw::_URC_FAILURE,
228 EHAction::None => return continue_unwind(exception_object, context),
229 EHAction::Cleanup(lpad) |
230 EHAction::Catch(lpad) => {
231 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0, exception_object as uintptr_t);
232 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
233 uw::_Unwind_SetIP(context, lpad);
234 return uw::_URC_INSTALL_CONTEXT;
236 EHAction::Terminate => return uw::_URC_FAILURE,
240 // On ARM EHABI the personality routine is responsible for actually
241 // unwinding a single stack frame before returning (ARM EHABI Sec. 6.1).
242 unsafe fn continue_unwind(exception_object: *mut uw::_Unwind_Exception,
243 context: *mut uw::_Unwind_Context)
244 -> uw::_Unwind_Reason_Code {
245 if __gnu_unwind_frame(exception_object, context) == uw::_URC_NO_REASON {
246 uw::_URC_CONTINUE_UNWIND
253 fn __gnu_unwind_frame(exception_object: *mut uw::_Unwind_Exception,
254 context: *mut uw::_Unwind_Context)
255 -> uw::_Unwind_Reason_Code;
259 unsafe fn find_eh_action(context: *mut uw::_Unwind_Context)
260 -> Result<EHAction, ()>
262 let lsda = uw::_Unwind_GetLanguageSpecificData(context) as *const u8;
263 let mut ip_before_instr: c_int = 0;
264 let ip = uw::_Unwind_GetIPInfo(context, &mut ip_before_instr);
265 let eh_context = EHContext {
266 // The return address points 1 byte past the call instruction,
267 // which could be in the next IP range in LSDA range table.
268 ip: if ip_before_instr != 0 { ip } else { ip - 1 },
269 func_start: uw::_Unwind_GetRegionStart(context),
270 get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
271 get_data_start: &|| uw::_Unwind_GetDataRelBase(context),
273 eh::find_eh_action(lsda, &eh_context)
276 // See docs in the `unwind` module.
277 #[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]
278 #[lang = "eh_unwind_resume"]
280 unsafe extern "C" fn rust_eh_unwind_resume(panic_ctx: *mut u8) -> ! {
281 uw::_Unwind_Resume(panic_ctx as *mut uw::_Unwind_Exception);
284 // Frame unwind info registration
286 // Each module's image contains a frame unwind info section (usually
287 // ".eh_frame"). When a module is loaded/unloaded into the process, the
288 // unwinder must be informed about the location of this section in memory. The
289 // methods of achieving that vary by the platform. On some (e.g., Linux), the
290 // unwinder can discover unwind info sections on its own (by dynamically
291 // enumerating currently loaded modules via the dl_iterate_phdr() API and
292 // finding their ".eh_frame" sections); Others, like Windows, require modules
293 // to actively register their unwind info sections via unwinder API.
295 // This module defines two symbols which are referenced and called from
296 // rsbegin.rs to register our information with the GCC runtime. The
297 // implementation of stack unwinding is (for now) deferred to libgcc_eh, however
298 // Rust crates use these Rust-specific entry points to avoid potential clashes
299 // with any GCC runtime.
300 #[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]
301 pub mod eh_frame_registry {
303 fn __register_frame_info(eh_frame_begin: *const u8, object: *mut u8);
304 fn __deregister_frame_info(eh_frame_begin: *const u8, object: *mut u8);
308 pub unsafe extern "C" fn rust_eh_register_frames(eh_frame_begin: *const u8, object: *mut u8) {
309 __register_frame_info(eh_frame_begin, object);
313 pub unsafe extern "C" fn rust_eh_unregister_frames(eh_frame_begin: *const u8,
315 __deregister_frame_info(eh_frame_begin, object);