src/libpanic_unwind/gcc.rs

   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.
   4 //
   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.
  10
  11 //! Implementation of panics backed by libgcc/libunwind (in some form)
  12 //!
  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
  20 //!
  21 //! ## A brief summary
  22 //!
  23 //! Exception handling happens in two phases: a search phase and a cleanup
  24 //! phase.
  25 //!
  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
  29 //! dynamic library).
  30 //!
  31 //! For each stack frame, it invokes the associated "personality routine", whose
  32 //! address is also stored in the unwind info section.
  33 //!
  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
  37 //! begins.
  38 //!
  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.
  45 //!
  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.
  48 //!
  49 //! ## `eh_personality` and `eh_unwind_resume`
  50 //!
  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.
  56
  57 #![allow(private_no_mangle_fns)]
  58
  59 use core::any::Any;
  60 use core::ptr;
  61 use alloc::boxed::Box;
  62
  63 use unwind as uw;
  64 use libc::{c_int, uintptr_t};
  65 use dwarf::eh::{self, EHContext, EHAction};
  66
  67 #[repr(C)]
  68 struct Exception {
  69     _uwe: uw::_Unwind_Exception,
  70     cause: Option<Box<Any + Send>>,
  71 }
  72
  73 pub unsafe fn panic(data: Box<Any + Send>) -> u32 {
  74     let exception = Box::new(Exception {
  75         _uwe: uw::_Unwind_Exception {
  76             exception_class: rust_exception_class(),
  77             exception_cleanup: exception_cleanup,
  78             private: [0; uw::unwinder_private_data_size],
  79         },
  80         cause: Some(data),
  81     });
  82     let exception_param = Box::into_raw(exception) as *mut uw::_Unwind_Exception;
  83     return uw::_Unwind_RaiseException(exception_param) as u32;
  84
  85     extern "C" fn exception_cleanup(_unwind_code: uw::_Unwind_Reason_Code,
  86                                     exception: *mut uw::_Unwind_Exception) {
  87         unsafe {
  88             let _: Box<Exception> = Box::from_raw(exception as *mut Exception);
  89         }
  90     }
  91 }
  92
  93 pub fn payload() -> *mut u8 {
  94     ptr::null_mut()
  95 }
  96
  97 pub unsafe fn cleanup(ptr: *mut u8) -> Box<Any + Send> {
  98     let my_ep = ptr as *mut Exception;
  99     let cause = (*my_ep).cause.take();
 100     uw::_Unwind_DeleteException(ptr as *mut _);
 101     cause.unwrap()
 102 }
 103
 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
 108     0x4d4f5a_00_52555354
 109 }
 110
 111
 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.
 117
 118 #[cfg(target_arch = "x86")]
 119 const UNWIND_DATA_REG: (i32, i32) = (0, 2); // EAX, EDX
 120
 121 #[cfg(target_arch = "x86_64")]
 122 const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX
 123
 124 #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
 125 const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1 / X0, X1
 126
 127 #[cfg(any(target_arch = "mips", target_arch = "mipsel"))]
 128 const UNWIND_DATA_REG: (i32, i32) = (4, 5); // A0, A1
 129
 130 #[cfg(any(target_arch = "powerpc", target_arch = "powerpc64"))]
 131 const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4 / X3, X4
 132
 133 // The following code is based on GCC's C and C++ personality routines.  For reference, see:
 134 // https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/libsupc++/eh_personality.cc
 135 // https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
 136
 137 // The personality routine for most of our targets, except ARM, which has a slightly different ABI
 138 // (however, iOS goes here as it uses SjLj unwinding).  Also, the 64-bit Windows implementation
 139 // lives in seh64_gnu.rs
 140 #[cfg(all(any(target_os = "ios", not(target_arch = "arm"))))]
 141 #[lang = "eh_personality"]
 142 #[no_mangle]
 143 #[allow(unused)]
 144 unsafe extern "C" fn rust_eh_personality(version: c_int,
 145                                          actions: uw::_Unwind_Action,
 146                                          exception_class: uw::_Unwind_Exception_Class,
 147                                          exception_object: *mut uw::_Unwind_Exception,
 148                                          context: *mut uw::_Unwind_Context)
 149                                          -> uw::_Unwind_Reason_Code {
 150     if version != 1 {
 151         return uw::_URC_FATAL_PHASE1_ERROR;
 152     }
 153     let eh_action = find_eh_action(context);
 154     if actions as i32 & uw::_UA_SEARCH_PHASE as i32 != 0 {
 155         match eh_action {
 156             EHAction::None | EHAction::Cleanup(_) => return uw::_URC_CONTINUE_UNWIND,
 157             EHAction::Catch(_) => return uw::_URC_HANDLER_FOUND,
 158             EHAction::Terminate => return uw::_URC_FATAL_PHASE1_ERROR,
 159         }
 160     } else {
 161         match eh_action {
 162             EHAction::None => return uw::_URC_CONTINUE_UNWIND,
 163             EHAction::Cleanup(lpad) | EHAction::Catch(lpad) => {
 164                 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0, exception_object as uintptr_t);
 165                 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
 166                 uw::_Unwind_SetIP(context, lpad);
 167                 return uw::_URC_INSTALL_CONTEXT;
 168             }
 169             EHAction::Terminate => return uw::_URC_FATAL_PHASE2_ERROR,
 170         }
 171     }
 172 }
 173
 174 // ARM EHABI personality routine.
 175 // http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
 176 #[cfg(all(target_arch = "arm", not(target_os = "ios")))]
 177 #[lang = "eh_personality"]
 178 #[no_mangle]
 179 unsafe extern "C" fn rust_eh_personality(state: uw::_Unwind_State,
 180                                          exception_object: *mut uw::_Unwind_Exception,
 181                                          context: *mut uw::_Unwind_Context)
 182                                         -> uw::_Unwind_Reason_Code {
 183     let state = state as c_int;
 184     let action = state & uw::_US_ACTION_MASK as c_int;
 185     let search_phase = if action == uw::_US_VIRTUAL_UNWIND_FRAME as c_int {
 186         // Backtraces on ARM will call the personality routine with
 187         // state == _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND. In those cases
 188         // we want to continue unwinding the stack, otherwise all our backtraces
 189         // would end at __rust_try
 190         if state & uw::_US_FORCE_UNWIND as c_int != 0 {
 191             return continue_unwind(exception_object, context)
 192         }
 193         true
 194     } else if action == uw::_US_UNWIND_FRAME_STARTING as c_int {
 195         false
 196     } else if action == uw::_US_UNWIND_FRAME_RESUME as c_int {
 197         return continue_unwind(exception_object, context);
 198     } else {
 199         return uw::_URC_FAILURE;
 200     };
 201
 202     // The DWARF unwinder assumes that _Unwind_Context holds things like the function
 203     // and LSDA pointers, however ARM EHABI places them into the exception object.
 204     // To preserve signatures of functions like _Unwind_GetLanguageSpecificData(), which
 205     // take only the context pointer, GCC personality routines stash a pointer to exception_object
 206     // in the context, using location reserved for ARM's "scratch register" (r12).
 207     uw::_Unwind_SetGR(context, uw::UNWIND_POINTER_REG, exception_object as uw::_Unwind_Ptr);
 208     // ...A more principled approach would be to provide the full definition of ARM's
 209     // _Unwind_Context in our libunwind bindings and fetch the required data from there directly,
 210     // bypassing DWARF compatibility functions.
 211
 212     let eh_action = find_eh_action(context);
 213     if search_phase {
 214         match eh_action {
 215             EHAction::None |
 216             EHAction::Cleanup(_) => return continue_unwind(exception_object, context),
 217             EHAction::Catch(_) => return uw::_URC_HANDLER_FOUND,
 218             EHAction::Terminate => return uw::_URC_FAILURE,
 219         }
 220     } else {
 221         match eh_action {
 222             EHAction::None => return continue_unwind(exception_object, context),
 223             EHAction::Cleanup(lpad) | EHAction::Catch(lpad) => {
 224                 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.0, exception_object as uintptr_t);
 225                 uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
 226                 uw::_Unwind_SetIP(context, lpad);
 227                 return uw::_URC_INSTALL_CONTEXT;
 228             }
 229             EHAction::Terminate => return uw::_URC_FAILURE,
 230         }
 231     }
 232
 233     // On ARM EHABI the personality routine is responsible for actually
 234     // unwinding a single stack frame before returning (ARM EHABI Sec. 6.1).
 235     unsafe fn continue_unwind(exception_object: *mut uw::_Unwind_Exception,
 236                               context: *mut uw::_Unwind_Context)
 237                               -> uw::_Unwind_Reason_Code {
 238         if __gnu_unwind_frame(exception_object, context) == uw::_URC_NO_REASON {
 239             uw::_URC_CONTINUE_UNWIND
 240         } else {
 241             uw::_URC_FAILURE
 242         }
 243     }
 244     // defined in libgcc
 245     extern "C" {
 246         fn __gnu_unwind_frame(exception_object: *mut uw::_Unwind_Exception,
 247                                 context: *mut uw::_Unwind_Context)
 248                                 -> uw::_Unwind_Reason_Code;
 249     }
 250 }
 251
 252 unsafe fn find_eh_action(context: *mut uw::_Unwind_Context) -> EHAction {
 253     let lsda = uw::_Unwind_GetLanguageSpecificData(context) as *const u8;
 254     let mut ip_before_instr: c_int = 0;
 255     let ip = uw::_Unwind_GetIPInfo(context, &mut ip_before_instr);
 256     let eh_context = EHContext {
 257         // The return address points 1 byte past the call instruction,
 258         // which could be in the next IP range in LSDA range table.
 259         ip: if ip_before_instr != 0 { ip } else { ip - 1 },
 260         func_start: uw::_Unwind_GetRegionStart(context),
 261         get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
 262         get_data_start: &|| uw::_Unwind_GetDataRelBase(context),
 263     };
 264     eh::find_eh_action(lsda, &eh_context)
 265 }
 266
 267 // *** Delete after a new snapshot ***
 268 #[cfg(all(stage0, any(target_os = "ios", not(target_arch = "arm"))))]
 269 #[lang = "eh_personality_catch"]
 270 #[no_mangle]
 271 pub unsafe extern "C" fn rust_eh_personality_catch(version: c_int,
 272                                                     actions: uw::_Unwind_Action,
 273                                                     exception_class: uw::_Unwind_Exception_Class,
 274                                                     ue_header: *mut uw::_Unwind_Exception,
 275                                                     context: *mut uw::_Unwind_Context)
 276                                                     -> uw::_Unwind_Reason_Code {
 277     rust_eh_personality(version, actions, exception_class, ue_header, context)
 278 }
 279
 280 // *** Delete after a new snapshot ***
 281 #[cfg(all(stage0, target_arch = "arm", not(target_os = "ios")))]
 282 #[lang = "eh_personality_catch"]
 283 #[no_mangle]
 284 pub unsafe extern "C" fn rust_eh_personality_catch(state: uw::_Unwind_State,
 285                                                     ue_header: *mut uw::_Unwind_Exception,
 286                                                     context: *mut uw::_Unwind_Context)
 287                                                     -> uw::_Unwind_Reason_Code {
 288     rust_eh_personality(state, ue_header, context)
 289 }
 290
 291 // See docs in the `unwind` module.
 292 #[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]
 293 #[lang = "eh_unwind_resume"]
 294 #[unwind]
 295 unsafe extern "C" fn rust_eh_unwind_resume(panic_ctx: *mut u8) -> ! {
 296     uw::_Unwind_Resume(panic_ctx as *mut uw::_Unwind_Exception);
 297 }
 298
 299 // Frame unwind info registration
 300 //
 301 // Each module's image contains a frame unwind info section (usually
 302 // ".eh_frame").  When a module is loaded/unloaded into the process, the
 303 // unwinder must be informed about the location of this section in memory. The
 304 // methods of achieving that vary by the platform.  On some (e.g. Linux), the
 305 // unwinder can discover unwind info sections on its own (by dynamically
 306 // enumerating currently loaded modules via the dl_iterate_phdr() API and
 307 // finding their ".eh_frame" sections); Others, like Windows, require modules
 308 // to actively register their unwind info sections via unwinder API.
 309 //
 310 // This module defines two symbols which are referenced and called from
 311 // rsbegin.rs to reigster our information with the GCC runtime. The
 312 // implementation of stack unwinding is (for now) deferred to libgcc_eh, however
 313 // Rust crates use these Rust-specific entry points to avoid potential clashes
 314 // with any GCC runtime.
 315 #[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]
 316 pub mod eh_frame_registry {
 317     #[link(name = "gcc_eh")]
 318     #[cfg(not(cargobuild))]
 319     extern "C" {}
 320
 321     extern "C" {
 322         fn __register_frame_info(eh_frame_begin: *const u8, object: *mut u8);
 323         fn __deregister_frame_info(eh_frame_begin: *const u8, object: *mut u8);
 324     }
 325
 326     #[no_mangle]
 327     pub unsafe extern "C" fn rust_eh_register_frames(eh_frame_begin: *const u8, object: *mut u8) {
 328         __register_frame_info(eh_frame_begin, object);
 329     }
 330
 331     #[no_mangle]
 332     pub unsafe extern "C" fn rust_eh_unregister_frames(eh_frame_begin: *const u8,
 333                                                        object: *mut u8) {
 334         __deregister_frame_info(eh_frame_begin, object);
 335     }
 336 }