library/panic_unwind/src/gcc.rs

   1 //! Implementation of panics backed by libgcc/libunwind (in some form).
   2 //!
   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
  10 //!
  11 //! ## A brief summary
  12 //!
  13 //! Exception handling happens in two phases: a search phase and a cleanup
  14 //! phase.
  15 //!
  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
  19 //! dynamic library).
  20 //!
  21 //! For each stack frame, it invokes the associated "personality routine", whose
  22 //! address is also stored in the unwind info section.
  23 //!
  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
  27 //! begins.
  28 //!
  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.
  35 //!
  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.
  38
  39 use alloc::boxed::Box;
  40 use core::any::Any;
  41
  42 use crate::dwarf::eh::{self, EHAction, EHContext};
  43 use libc::{c_int, uintptr_t};
  44 use unwind as uw;
  45
  46 #[repr(C)]
  47 struct Exception {
  48     _uwe: uw::_Unwind_Exception,
  49     cause: Box<dyn Any + Send>,
  50 }
  51
  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(),
  56             exception_cleanup,
  57             private: [0; uw::unwinder_private_data_size],
  58         },
  59         cause: data,
  60     });
  61     let exception_param = Box::into_raw(exception) as *mut uw::_Unwind_Exception;
  62     return uw::_Unwind_RaiseException(exception_param) as u32;
  63
  64     extern "C" fn exception_cleanup(
  65         _unwind_code: uw::_Unwind_Reason_Code,
  66         exception: *mut uw::_Unwind_Exception,
  67     ) {
  68         unsafe {
  69             let _: Box<Exception> = Box::from_raw(exception as *mut Exception);
  70             super::__rust_drop_panic();
  71         }
  72     }
  73 }
  74
  75 pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
  76     let exception = ptr as *mut uw::_Unwind_Exception;
  77     if (*exception).exception_class != rust_exception_class() {
  78         uw::_Unwind_DeleteException(exception);
  79         super::__rust_foreign_exception();
  80     } else {
  81         let exception = Box::from_raw(exception as *mut Exception);
  82         exception.cause
  83     }
  84 }
  85
  86 // Rust's exception class identifier.  This is used by personality routines to
  87 // determine whether the exception was thrown by their own runtime.
  88 fn rust_exception_class() -> uw::_Unwind_Exception_Class {
  89     // M O Z \0  R U S T -- vendor, language
  90     0x4d4f5a_00_52555354
  91 }
  92
  93 // Register ids were lifted from LLVM's TargetLowering::getExceptionPointerRegister()
  94 // and TargetLowering::getExceptionSelectorRegister() for each architecture,
  95 // then mapped to DWARF register numbers via register definition tables
  96 // (typically <arch>RegisterInfo.td, search for "DwarfRegNum").
  97 // See also http://llvm.org/docs/WritingAnLLVMBackend.html#defining-a-register.
  98
  99 #[cfg(target_arch = "x86")]
 100 const UNWIND_DATA_REG: (i32, i32) = (0, 2); // EAX, EDX
 101
 102 #[cfg(target_arch = "x86_64")]
 103 const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX
 104
 105 #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
 106 const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1 / X0, X1
 107
 108 #[cfg(any(target_arch = "mips", target_arch = "mips64"))]
 109 const UNWIND_DATA_REG: (i32, i32) = (4, 5); // A0, A1
 110
 111 #[cfg(any(target_arch = "powerpc", target_arch = "powerpc64"))]
 112 const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4 / X3, X4
 113
 114 #[cfg(target_arch = "s390x")]
 115 const UNWIND_DATA_REG: (i32, i32) = (6, 7); // R6, R7
 116
 117 #[cfg(any(target_arch = "sparc", target_arch = "sparc64"))]
 118 const UNWIND_DATA_REG: (i32, i32) = (24, 25); // I0, I1
 119
 120 #[cfg(target_arch = "hexagon")]
 121 const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1
 122
 123 #[cfg(any(target_arch = "riscv64", target_arch = "riscv32"))]
 124 const UNWIND_DATA_REG: (i32, i32) = (10, 11); // x10, x11
 125
 126 // The following code is based on GCC's C and C++ personality routines.  For reference, see:
 127 // https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/libsupc++/eh_personality.cc
 128 // https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
 129
 130 cfg_if::cfg_if! {
 131     if #[cfg(all(target_arch = "arm", not(target_os = "ios"), not(target_os = "netbsd")))] {
 132         // ARM EHABI personality routine.
 133         // http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
 134         //
 135         // iOS uses the default routine instead since it uses SjLj unwinding.
 136         #[lang = "eh_personality"]
 137         unsafe extern "C" fn rust_eh_personality(state: uw::_Unwind_State,
 138                                                  exception_object: *mut uw::_Unwind_Exception,
 139                                                  context: *mut uw::_Unwind_Context)
 140                                                  -> uw::_Unwind_Reason_Code {
 141             let state = state as c_int;
 142             let action = state & uw::_US_ACTION_MASK as c_int;
 143             let search_phase = if action == uw::_US_VIRTUAL_UNWIND_FRAME as c_int {
 144                 // Backtraces on ARM will call the personality routine with
 145                 // state == _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND. In those cases
 146                 // we want to continue unwinding the stack, otherwise all our backtraces
 147                 // would end at __rust_try
 148                 if state & uw::_US_FORCE_UNWIND as c_int != 0 {
 149                     return continue_unwind(exception_object, context);
 150                 }
 151                 true
 152             } else if action == uw::_US_UNWIND_FRAME_STARTING as c_int {
 153                 false
 154             } else if action == uw::_US_UNWIND_FRAME_RESUME as c_int {
 155                 return continue_unwind(exception_object, context);
 156             } else {
 157                 return uw::_URC_FAILURE;
 158             };
 159
 160             // The DWARF unwinder assumes that _Unwind_Context holds things like the function
 161             // and LSDA pointers, however ARM EHABI places them into the exception object.
 162             // To preserve signatures of functions like _Unwind_GetLanguageSpecificData(), which
 163             // take only the context pointer, GCC personality routines stash a pointer to
 164             // exception_object in the context, using location reserved for ARM's
 165             // "scratch register" (r12).
 166             uw::_Unwind_SetGR(context,
 167                               uw::UNWIND_POINTER_REG,
 168                               exception_object as uw::_Unwind_Ptr);
 169             // ...A more principled approach would be to provide the full definition of ARM's
 170             // _Unwind_Context in our libunwind bindings and fetch the required data from there
 171             // directly, bypassing DWARF compatibility functions.
 172
 173             let eh_action = match find_eh_action(context) {
 174                 Ok(action) => action,
 175                 Err(_) => return uw::_URC_FAILURE,
 176             };
 177             if search_phase {
 178                 match eh_action {
 179                     EHAction::None |
 180                     EHAction::Cleanup(_) => return continue_unwind(exception_object, context),
 181                     EHAction::Catch(_) => {
 182                         // EHABI requires the personality routine to update the
 183                         // SP value in the barrier cache of the exception object.
 184                         (*exception_object).private[5] =
 185                             uw::_Unwind_GetGR(context, uw::UNWIND_SP_REG);
 186                         return uw::_URC_HANDLER_FOUND;
 187                     }
 188                     EHAction::Terminate => return uw::_URC_FAILURE,
 189                 }
 190             } else {
 191                 match eh_action {
 192                     EHAction::None => return continue_unwind(exception_object, context),
 193                     EHAction::Cleanup(lpad) |
 194                     EHAction::Catch(lpad) => {
 195                         uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0,
 196                                           exception_object as uintptr_t);
 197                         uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
 198                         uw::_Unwind_SetIP(context, lpad);
 199                         return uw::_URC_INSTALL_CONTEXT;
 200                     }
 201                     EHAction::Terminate => return uw::_URC_FAILURE,
 202                 }
 203             }
 204
 205             // On ARM EHABI the personality routine is responsible for actually
 206             // unwinding a single stack frame before returning (ARM EHABI Sec. 6.1).
 207             unsafe fn continue_unwind(exception_object: *mut uw::_Unwind_Exception,
 208                                       context: *mut uw::_Unwind_Context)
 209                                       -> uw::_Unwind_Reason_Code {
 210                 if __gnu_unwind_frame(exception_object, context) == uw::_URC_NO_REASON {
 211                     uw::_URC_CONTINUE_UNWIND
 212                 } else {
 213                     uw::_URC_FAILURE
 214                 }
 215             }
 216             // defined in libgcc
 217             extern "C" {
 218                 fn __gnu_unwind_frame(exception_object: *mut uw::_Unwind_Exception,
 219                                       context: *mut uw::_Unwind_Context)
 220                                       -> uw::_Unwind_Reason_Code;
 221             }
 222         }
 223     } else {
 224         // Default personality routine, which is used directly on most targets
 225         // and indirectly on Windows x86_64 via SEH.
 226         unsafe extern "C" fn rust_eh_personality_impl(version: c_int,
 227                                                       actions: uw::_Unwind_Action,
 228                                                       _exception_class: uw::_Unwind_Exception_Class,
 229                                                       exception_object: *mut uw::_Unwind_Exception,
 230                                                       context: *mut uw::_Unwind_Context)
 231                                                       -> uw::_Unwind_Reason_Code {
 232             if version != 1 {
 233                 return uw::_URC_FATAL_PHASE1_ERROR;
 234             }
 235             let eh_action = match find_eh_action(context) {
 236                 Ok(action) => action,
 237                 Err(_) => return uw::_URC_FATAL_PHASE1_ERROR,
 238             };
 239             if actions as i32 & uw::_UA_SEARCH_PHASE as i32 != 0 {
 240                 match eh_action {
 241                     EHAction::None |
 242                     EHAction::Cleanup(_) => uw::_URC_CONTINUE_UNWIND,
 243                     EHAction::Catch(_) => uw::_URC_HANDLER_FOUND,
 244                     EHAction::Terminate => uw::_URC_FATAL_PHASE1_ERROR,
 245                 }
 246             } else {
 247                 match eh_action {
 248                     EHAction::None => uw::_URC_CONTINUE_UNWIND,
 249                     EHAction::Cleanup(lpad) |
 250                     EHAction::Catch(lpad) => {
 251                         uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0,
 252                             exception_object as uintptr_t);
 253                         uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
 254                         uw::_Unwind_SetIP(context, lpad);
 255                         uw::_URC_INSTALL_CONTEXT
 256                     }
 257                     EHAction::Terminate => uw::_URC_FATAL_PHASE2_ERROR,
 258                 }
 259             }
 260         }
 261
 262         cfg_if::cfg_if! {
 263             if #[cfg(all(windows, target_arch = "x86_64", target_env = "gnu"))] {
 264                 // On x86_64 MinGW targets, the unwinding mechanism is SEH however the unwind
 265                 // handler data (aka LSDA) uses GCC-compatible encoding.
 266                 #[lang = "eh_personality"]
 267                 #[allow(nonstandard_style)]
 268                 unsafe extern "C" fn rust_eh_personality(exceptionRecord: *mut uw::EXCEPTION_RECORD,
 269                         establisherFrame: uw::LPVOID,
 270                         contextRecord: *mut uw::CONTEXT,
 271                         dispatcherContext: *mut uw::DISPATCHER_CONTEXT)
 272                         -> uw::EXCEPTION_DISPOSITION {
 273                     uw::_GCC_specific_handler(exceptionRecord,
 274                                              establisherFrame,
 275                                              contextRecord,
 276                                              dispatcherContext,
 277                                              rust_eh_personality_impl)
 278                 }
 279             } else {
 280                 // The personality routine for most of our targets.
 281                 #[lang = "eh_personality"]
 282                 unsafe extern "C" fn rust_eh_personality(version: c_int,
 283                         actions: uw::_Unwind_Action,
 284                         exception_class: uw::_Unwind_Exception_Class,
 285                         exception_object: *mut uw::_Unwind_Exception,
 286                         context: *mut uw::_Unwind_Context)
 287                         -> uw::_Unwind_Reason_Code {
 288                     rust_eh_personality_impl(version,
 289                                              actions,
 290                                              exception_class,
 291                                              exception_object,
 292                                              context)
 293                 }
 294             }
 295         }
 296     }
 297 }
 298
 299 unsafe fn find_eh_action(context: *mut uw::_Unwind_Context) -> 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),
 310     };
 311     eh::find_eh_action(lsda, &eh_context)
 312 }
 313
 314 // Frame unwind info registration
 315 //
 316 // Each module's image contains a frame unwind info section (usually
 317 // ".eh_frame").  When a module is loaded/unloaded into the process, the
 318 // unwinder must be informed about the location of this section in memory. The
 319 // methods of achieving that vary by the platform.  On some (e.g., Linux), the
 320 // unwinder can discover unwind info sections on its own (by dynamically
 321 // enumerating currently loaded modules via the dl_iterate_phdr() API and
 322 // finding their ".eh_frame" sections); Others, like Windows, require modules
 323 // to actively register their unwind info sections via unwinder API.
 324 //
 325 // This module defines two symbols which are referenced and called from
 326 // rsbegin.rs to register our information with the GCC runtime. The
 327 // implementation of stack unwinding is (for now) deferred to libgcc_eh, however
 328 // Rust crates use these Rust-specific entry points to avoid potential clashes
 329 // with any GCC runtime.
 330 #[cfg(all(target_os = "windows", target_arch = "x86", target_env = "gnu"))]
 331 pub mod eh_frame_registry {
 332     extern "C" {
 333         fn __register_frame_info(eh_frame_begin: *const u8, object: *mut u8);
 334         fn __deregister_frame_info(eh_frame_begin: *const u8, object: *mut u8);
 335     }
 336
 337     #[rustc_std_internal_symbol]
 338     pub unsafe extern "C" fn rust_eh_register_frames(eh_frame_begin: *const u8, object: *mut u8) {
 339         __register_frame_info(eh_frame_begin, object);
 340     }
 341
 342     #[rustc_std_internal_symbol]
 343     pub unsafe extern "C" fn rust_eh_unregister_frames(eh_frame_begin: *const u8, object: *mut u8) {
 344         __deregister_frame_info(eh_frame_begin, object);
 345     }
 346 }