1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Implementation of panics backed by libgcc/libunwind (in some form)
13 //! For background on exception handling and stack unwinding please see
14 //! "Exception Handling in LLVM" (llvm.org/docs/ExceptionHandling.html) and
15 //! documents linked from it.
16 //! These are also good reads:
17 //! http://mentorembedded.github.io/cxx-abi/abi-eh.html
18 //! http://monoinfinito.wordpress.com/series/exception-handling-in-c/
19 //! http://www.airs.com/blog/index.php?s=exception+frames
21 //! ## A brief summary
23 //! Exception handling happens in two phases: a search phase and a cleanup
26 //! In both phases the unwinder walks stack frames from top to bottom using
27 //! information from the stack frame unwind sections of the current process's
28 //! modules ("module" here refers to an OS module, i.e., an executable or a
31 //! For each stack frame, it invokes the associated "personality routine", whose
32 //! address is also stored in the unwind info section.
34 //! In the search phase, the job of a personality routine is to examine
35 //! exception object being thrown, and to decide whether it should be caught at
36 //! that stack frame. Once the handler frame has been identified, cleanup phase
39 //! In the cleanup phase, the unwinder invokes each personality routine again.
40 //! This time it decides which (if any) cleanup code needs to be run for
41 //! the current stack frame. If so, the control is transferred to a special
42 //! branch in the function body, the "landing pad", which invokes destructors,
43 //! frees memory, etc. At the end of the landing pad, control is transferred
44 //! back to the unwinder and unwinding resumes.
46 //! Once stack has been unwound down to the handler frame level, unwinding stops
47 //! and the last personality routine transfers control to the catch block.
49 //! ## `eh_personality` and `eh_unwind_resume`
51 //! These language items are used by the compiler when generating unwind info.
52 //! The first one is the personality routine described above. The second one
53 //! allows compilation target to customize the process of resuming unwind at the
54 //! end of the landing pads. `eh_unwind_resume` is used only if
55 //! `custom_unwind_resume` flag in the target options is set.
57 #![allow(private_no_mangle_fns)]
61 use alloc::boxed::Box;
64 use libc::{c_int, uintptr_t};
65 use dwarf::eh::{self, EHContext, EHAction};
69 _uwe: uw::_Unwind_Exception,
70 cause: Option<Box<dyn Any + Send>>,
73 pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
74 let exception = Box::new(Exception {
75 _uwe: uw::_Unwind_Exception {
76 exception_class: rust_exception_class(),
78 private: [0; uw::unwinder_private_data_size],
82 let exception_param = Box::into_raw(exception) as *mut uw::_Unwind_Exception;
83 return uw::_Unwind_RaiseException(exception_param) as u32;
85 extern "C" fn exception_cleanup(_unwind_code: uw::_Unwind_Reason_Code,
86 exception: *mut uw::_Unwind_Exception) {
88 let _: Box<Exception> = Box::from_raw(exception as *mut Exception);
93 pub fn payload() -> *mut u8 {
97 pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
98 let my_ep = ptr as *mut Exception;
99 let cause = (*my_ep).cause.take();
100 uw::_Unwind_DeleteException(ptr as *mut _);
104 // Rust's exception class identifier. This is used by personality routines to
105 // determine whether the exception was thrown by their own runtime.
106 fn rust_exception_class() -> uw::_Unwind_Exception_Class {
107 // M O Z \0 R U S T -- vendor, language
112 // Register ids were lifted from LLVM's TargetLowering::getExceptionPointerRegister()
113 // and TargetLowering::getExceptionSelectorRegister() for each architecture,
114 // then mapped to DWARF register numbers via register definition tables
115 // (typically <arch>RegisterInfo.td, search for "DwarfRegNum").
116 // See also http://llvm.org/docs/WritingAnLLVMBackend.html#defining-a-register.
118 #[cfg(target_arch = "x86")]
119 const UNWIND_DATA_REG: (i32, i32) = (0, 2); // EAX, EDX
121 #[cfg(target_arch = "x86_64")]
122 const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX
124 #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
125 const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1 / X0, X1
127 #[cfg(any(target_arch = "mips", target_arch = "mips64"))]
128 const UNWIND_DATA_REG: (i32, i32) = (4, 5); // A0, A1
130 #[cfg(any(target_arch = "powerpc", target_arch = "powerpc64"))]
131 const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4 / X3, X4
133 #[cfg(target_arch = "s390x")]
134 const UNWIND_DATA_REG: (i32, i32) = (6, 7); // R6, R7
136 #[cfg(target_arch = "sparc64")]
137 const UNWIND_DATA_REG: (i32, i32) = (24, 25); // I0, I1
139 // The following code is based on GCC's C and C++ personality routines. For reference, see:
140 // https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/libsupc++/eh_personality.cc
141 // https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
143 // The personality routine for most of our targets, except ARM, which has a slightly different ABI
144 // (however, iOS goes here as it uses SjLj unwinding). Also, the 64-bit Windows implementation
145 // lives in seh64_gnu.rs
146 #[cfg(all(any(target_os = "ios", target_os = "netbsd", not(target_arch = "arm"))))]
147 #[lang = "eh_personality"]
150 unsafe extern "C" fn rust_eh_personality(version: c_int,
151 actions: uw::_Unwind_Action,
152 exception_class: uw::_Unwind_Exception_Class,
153 exception_object: *mut uw::_Unwind_Exception,
154 context: *mut uw::_Unwind_Context)
155 -> uw::_Unwind_Reason_Code {
157 return uw::_URC_FATAL_PHASE1_ERROR;
159 let eh_action = match find_eh_action(context) {
160 Ok(action) => action,
161 Err(_) => return uw::_URC_FATAL_PHASE1_ERROR,
163 if actions as i32 & uw::_UA_SEARCH_PHASE as i32 != 0 {
166 EHAction::Cleanup(_) => return uw::_URC_CONTINUE_UNWIND,
167 EHAction::Catch(_) => return uw::_URC_HANDLER_FOUND,
168 EHAction::Terminate => return uw::_URC_FATAL_PHASE1_ERROR,
172 EHAction::None => return uw::_URC_CONTINUE_UNWIND,
173 EHAction::Cleanup(lpad) |
174 EHAction::Catch(lpad) => {
175 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0, exception_object as uintptr_t);
176 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
177 uw::_Unwind_SetIP(context, lpad);
178 return uw::_URC_INSTALL_CONTEXT;
180 EHAction::Terminate => return uw::_URC_FATAL_PHASE2_ERROR,
185 // ARM EHABI personality routine.
186 // http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
187 #[cfg(all(target_arch = "arm", not(target_os = "ios"), not(target_os = "netbsd")))]
188 #[lang = "eh_personality"]
190 unsafe extern "C" fn rust_eh_personality(state: uw::_Unwind_State,
191 exception_object: *mut uw::_Unwind_Exception,
192 context: *mut uw::_Unwind_Context)
193 -> uw::_Unwind_Reason_Code {
194 let state = state as c_int;
195 let action = state & uw::_US_ACTION_MASK as c_int;
196 let search_phase = if action == uw::_US_VIRTUAL_UNWIND_FRAME as c_int {
197 // Backtraces on ARM will call the personality routine with
198 // state == _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND. In those cases
199 // we want to continue unwinding the stack, otherwise all our backtraces
200 // would end at __rust_try
201 if state & uw::_US_FORCE_UNWIND as c_int != 0 {
202 return continue_unwind(exception_object, context);
205 } else if action == uw::_US_UNWIND_FRAME_STARTING as c_int {
207 } else if action == uw::_US_UNWIND_FRAME_RESUME as c_int {
208 return continue_unwind(exception_object, context);
210 return uw::_URC_FAILURE;
213 // The DWARF unwinder assumes that _Unwind_Context holds things like the function
214 // and LSDA pointers, however ARM EHABI places them into the exception object.
215 // To preserve signatures of functions like _Unwind_GetLanguageSpecificData(), which
216 // take only the context pointer, GCC personality routines stash a pointer to exception_object
217 // in the context, using location reserved for ARM's "scratch register" (r12).
218 uw::_Unwind_SetGR(context,
219 uw::UNWIND_POINTER_REG,
220 exception_object as uw::_Unwind_Ptr);
221 // ...A more principled approach would be to provide the full definition of ARM's
222 // _Unwind_Context in our libunwind bindings and fetch the required data from there directly,
223 // bypassing DWARF compatibility functions.
225 let eh_action = match find_eh_action(context) {
226 Ok(action) => action,
227 Err(_) => return uw::_URC_FAILURE,
232 EHAction::Cleanup(_) => return continue_unwind(exception_object, context),
233 EHAction::Catch(_) => return uw::_URC_HANDLER_FOUND,
234 EHAction::Terminate => return uw::_URC_FAILURE,
238 EHAction::None => return continue_unwind(exception_object, context),
239 EHAction::Cleanup(lpad) |
240 EHAction::Catch(lpad) => {
241 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0, exception_object as uintptr_t);
242 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
243 uw::_Unwind_SetIP(context, lpad);
244 return uw::_URC_INSTALL_CONTEXT;
246 EHAction::Terminate => return uw::_URC_FAILURE,
250 // On ARM EHABI the personality routine is responsible for actually
251 // unwinding a single stack frame before returning (ARM EHABI Sec. 6.1).
252 unsafe fn continue_unwind(exception_object: *mut uw::_Unwind_Exception,
253 context: *mut uw::_Unwind_Context)
254 -> uw::_Unwind_Reason_Code {
255 if __gnu_unwind_frame(exception_object, context) == uw::_URC_NO_REASON {
256 uw::_URC_CONTINUE_UNWIND
263 fn __gnu_unwind_frame(exception_object: *mut uw::_Unwind_Exception,
264 context: *mut uw::_Unwind_Context)
265 -> uw::_Unwind_Reason_Code;
269 unsafe fn find_eh_action(context: *mut uw::_Unwind_Context)
270 -> Result<EHAction, ()>
272 let lsda = uw::_Unwind_GetLanguageSpecificData(context) as *const u8;
273 let mut ip_before_instr: c_int = 0;
274 let ip = uw::_Unwind_GetIPInfo(context, &mut ip_before_instr);
275 let eh_context = EHContext {
276 // The return address points 1 byte past the call instruction,
277 // which could be in the next IP range in LSDA range table.
278 ip: if ip_before_instr != 0 { ip } else { ip - 1 },
279 func_start: uw::_Unwind_GetRegionStart(context),
280 get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
281 get_data_start: &|| uw::_Unwind_GetDataRelBase(context),
283 eh::find_eh_action(lsda, &eh_context)
286 // See docs in the `unwind` module.
287 #[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]
288 #[lang = "eh_unwind_resume"]
290 unsafe extern "C" fn rust_eh_unwind_resume(panic_ctx: *mut u8) -> ! {
291 uw::_Unwind_Resume(panic_ctx as *mut uw::_Unwind_Exception);
294 // Frame unwind info registration
296 // Each module's image contains a frame unwind info section (usually
297 // ".eh_frame"). When a module is loaded/unloaded into the process, the
298 // unwinder must be informed about the location of this section in memory. The
299 // methods of achieving that vary by the platform. On some (e.g., Linux), the
300 // unwinder can discover unwind info sections on its own (by dynamically
301 // enumerating currently loaded modules via the dl_iterate_phdr() API and
302 // finding their ".eh_frame" sections); Others, like Windows, require modules
303 // to actively register their unwind info sections via unwinder API.
305 // This module defines two symbols which are referenced and called from
306 // rsbegin.rs to register our information with the GCC runtime. The
307 // implementation of stack unwinding is (for now) deferred to libgcc_eh, however
308 // Rust crates use these Rust-specific entry points to avoid potential clashes
309 // with any GCC runtime.
310 #[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]
311 pub mod eh_frame_registry {
313 fn __register_frame_info(eh_frame_begin: *const u8, object: *mut u8);
314 fn __deregister_frame_info(eh_frame_begin: *const u8, object: *mut u8);
318 pub unsafe extern "C" fn rust_eh_register_frames(eh_frame_begin: *const u8, object: *mut u8) {
319 __register_frame_info(eh_frame_begin, object);
323 pub unsafe extern "C" fn rust_eh_unregister_frames(eh_frame_begin: *const u8,
325 __deregister_frame_info(eh_frame_begin, object);