#
std/sys/personality/
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//!  * <https://nicolasbrailo.github.io/blog/projects_texts/13exceptionsunderthehood.html>
    9//!  * <https://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#![forbid(unsafe_op_in_unsafe_fn)]
    39
    40use unwind as uw;
    41
    42use super::dwarf::eh::{self, EHAction, EHContext};
    43use crate::ffi::c_int;
    44
    45// Register ids were lifted from LLVM's TargetLowering::getExceptionPointerRegister()
    46// and TargetLowering::getExceptionSelectorRegister() for each architecture,
    47// then mapped to DWARF register numbers via register definition tables
    48// (typically <arch>RegisterInfo.td, search for "DwarfRegNum").
    49// See also https://llvm.org/docs/WritingAnLLVMBackend.html#defining-a-register.
    50
    51#[cfg(target_arch = "x86")]
    52const UNWIND_DATA_REG: (i32, i32) = (0, 2); // EAX, EDX
    53
    54#[cfg(target_arch = "x86_64")]
    55const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX
    56
    57#[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
    58const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1 / X0, X1
    59
    60#[cfg(target_arch = "m68k")]
    61const UNWIND_DATA_REG: (i32, i32) = (0, 1); // D0, D1
    62
    63#[cfg(any(
    64    target_arch = "mips",
    65    target_arch = "mips32r6",
    66    target_arch = "mips64",
    67    target_arch = "mips64r6"
    68))]
    69const UNWIND_DATA_REG: (i32, i32) = (4, 5); // A0, A1
    70
    71#[cfg(target_arch = "csky")]
    72const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1
    73
    74#[cfg(any(target_arch = "powerpc", target_arch = "powerpc64"))]
    75const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4 / X3, X4
    76
    77#[cfg(target_arch = "s390x")]
    78const UNWIND_DATA_REG: (i32, i32) = (6, 7); // R6, R7
    79
    80#[cfg(any(target_arch = "sparc", target_arch = "sparc64"))]
    81const UNWIND_DATA_REG: (i32, i32) = (24, 25); // I0, I1
    82
    83#[cfg(target_arch = "hexagon")]
    84const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1
    85
    86#[cfg(any(target_arch = "riscv64", target_arch = "riscv32"))]
    87const UNWIND_DATA_REG: (i32, i32) = (10, 11); // x10, x11
    88
    89#[cfg(any(target_arch = "loongarch32", target_arch = "loongarch64"))]
    90const UNWIND_DATA_REG: (i32, i32) = (4, 5); // a0, a1
    91
    92// The following code is based on GCC's C and C++ personality routines.  For reference, see:
    93// https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/libsupc++/eh_personality.cc
    94// https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
    95
    96cfg_if::cfg_if! {
    97    if #[cfg(all(
    98        target_arch = "arm",
    99        not(target_vendor = "apple"),
    100        not(target_os = "netbsd"),
    101    ))] {
    102        /// personality fn called by [ARM EHABI][armeabi-eh]
    103        ///
    104        /// 32-bit ARM on iOS/tvOS/watchOS does not use ARM EHABI, it uses
    105        /// either "setjmp-longjmp" unwinding or DWARF CFI unwinding, which is
    106        /// handled by the default routine.
    107        ///
    108        /// [armeabi-eh]: https://web.archive.org/web/20190728160938/https://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
    109        #[lang = "eh_personality"]
    110        unsafe extern "C" fn rust_eh_personality(
    111            state: uw::_Unwind_State,
    112            exception_object: *mut uw::_Unwind_Exception,
    113            context: *mut uw::_Unwind_Context,
    114        ) -> uw::_Unwind_Reason_Code {
    115            unsafe {
    116                let state = state as c_int;
    117                let action = state & uw::_US_ACTION_MASK as c_int;
    118                let search_phase = if action == uw::_US_VIRTUAL_UNWIND_FRAME as c_int {
    119                    // Backtraces on ARM will call the personality routine with
    120                    // state == _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND. In those cases
    121                    // we want to continue unwinding the stack, otherwise all our backtraces
    122                    // would end at __rust_try
    123                    if state & uw::_US_FORCE_UNWIND as c_int != 0 {
    124                        return continue_unwind(exception_object, context);
    125                    }
    126                    true
    127                } else if action == uw::_US_UNWIND_FRAME_STARTING as c_int {
    128                    false
    129                } else if action == uw::_US_UNWIND_FRAME_RESUME as c_int {
    130                    return continue_unwind(exception_object, context);
    131                } else {
    132                    return uw::_URC_FAILURE;
    133                };
    134
    135                // The DWARF unwinder assumes that _Unwind_Context holds things like the function
    136                // and LSDA pointers, however ARM EHABI places them into the exception object.
    137                // To preserve signatures of functions like _Unwind_GetLanguageSpecificData(), which
    138                // take only the context pointer, GCC personality routines stash a pointer to
    139                // exception_object in the context, using location reserved for ARM's
    140                // "scratch register" (r12).
    141                uw::_Unwind_SetGR(context, uw::UNWIND_POINTER_REG, exception_object as uw::_Unwind_Ptr);
    142                // ...A more principled approach would be to provide the full definition of ARM's
    143                // _Unwind_Context in our libunwind bindings and fetch the required data from there
    144                // directly, bypassing DWARF compatibility functions.
    145
    146                let eh_action = match find_eh_action(context) {
    147                    Ok(action) => action,
    148                    Err(_) => return uw::_URC_FAILURE,
    149                };
    150                if search_phase {
    151                    match eh_action {
    152                        EHAction::None | EHAction::Cleanup(_) => {
    153                            return continue_unwind(exception_object, context);
    154                        }
    155                        EHAction::Catch(_) | EHAction::Filter(_) => {
    156                            // EHABI requires the personality routine to update the
    157                            // SP value in the barrier cache of the exception object.
    158                            (*exception_object).private[5] =
    159                                uw::_Unwind_GetGR(context, uw::UNWIND_SP_REG);
    160                            return uw::_URC_HANDLER_FOUND;
    161                        }
    162                        EHAction::Terminate => return uw::_URC_FAILURE,
    163                    }
    164                } else {
    165                    match eh_action {
    166                        EHAction::None => return continue_unwind(exception_object, context),
    167                        EHAction::Filter(_) if state & uw::_US_FORCE_UNWIND as c_int != 0 => return continue_unwind(exception_object, context),
    168                        EHAction::Cleanup(lpad) | EHAction::Catch(lpad) | EHAction::Filter(lpad) => {
    169                            uw::_Unwind_SetGR(
    170                                context,
    171                                UNWIND_DATA_REG.0,
    172                                exception_object as uw::_Unwind_Ptr,
    173                            );
    174                            uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, core::ptr::null());
    175                            uw::_Unwind_SetIP(context, lpad);
    176                            return uw::_URC_INSTALL_CONTEXT;
    177                        }
    178                        EHAction::Terminate => return uw::_URC_FAILURE,
    179                    }
    180                }
    181
    182                // On ARM EHABI the personality routine is responsible for actually
    183                // unwinding a single stack frame before returning (ARM EHABI Sec. 6.1).
    184                unsafe fn continue_unwind(
    185                    exception_object: *mut uw::_Unwind_Exception,
    186                    context: *mut uw::_Unwind_Context,
    187                ) -> uw::_Unwind_Reason_Code {
    188                    unsafe {
    189                        if __gnu_unwind_frame(exception_object, context) == uw::_URC_NO_REASON {
    190                            uw::_URC_CONTINUE_UNWIND
    191                        } else {
    192                            uw::_URC_FAILURE
    193                        }
    194                    }
    195                }
    196                // defined in libgcc
    197                unsafe extern "C" {
    198                    fn __gnu_unwind_frame(
    199                        exception_object: *mut uw::_Unwind_Exception,
    200                        context: *mut uw::_Unwind_Context,
    201                    ) -> uw::_Unwind_Reason_Code;
    202                }
    203            }
    204        }
    205    } else {
    206        /// Default personality routine, which is used directly on most targets
    207        /// and indirectly on Windows x86_64 and AArch64 via SEH.
    208        unsafe extern "C" fn rust_eh_personality_impl(
    209            version: c_int,
    210            actions: uw::_Unwind_Action,
    211            _exception_class: uw::_Unwind_Exception_Class,
    212            exception_object: *mut uw::_Unwind_Exception,
    213            context: *mut uw::_Unwind_Context,
    214        ) -> uw::_Unwind_Reason_Code {
    215            unsafe {
    216                if version != 1 {
    217                    return uw::_URC_FATAL_PHASE1_ERROR;
    218                }
    219                let eh_action = match find_eh_action(context) {
    220                    Ok(action) => action,
    221                    Err(_) => return uw::_URC_FATAL_PHASE1_ERROR,
    222                };
    223                if actions & uw::_UA_SEARCH_PHASE != 0 {
    224                    match eh_action {
    225                        EHAction::None | EHAction::Cleanup(_) => uw::_URC_CONTINUE_UNWIND,
    226                        EHAction::Catch(_) | EHAction::Filter(_) => uw::_URC_HANDLER_FOUND,
    227                        EHAction::Terminate => uw::_URC_FATAL_PHASE1_ERROR,
    228                    }
    229                } else {
    230                    match eh_action {
    231                        EHAction::None => uw::_URC_CONTINUE_UNWIND,
    232                        // Forced unwinding hits a terminate action.
    233                        EHAction::Filter(_) if actions & uw::_UA_FORCE_UNWIND != 0 => uw::_URC_CONTINUE_UNWIND,
    234                        EHAction::Cleanup(lpad) | EHAction::Catch(lpad) | EHAction::Filter(lpad) => {
    235                            uw::_Unwind_SetGR(
    236                                context,
    237                                UNWIND_DATA_REG.0,
    238                                exception_object.cast(),
    239                            );
    240                            uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, core::ptr::null());
    241                            uw::_Unwind_SetIP(context, lpad);
    242                            uw::_URC_INSTALL_CONTEXT
    243                        }
    244                        EHAction::Terminate => uw::_URC_FATAL_PHASE2_ERROR,
    245                    }
    246                }
    247            }
    248        }
    249
    250        cfg_if::cfg_if! {
    251            if #[cfg(any(
    252                    all(windows, any(target_arch = "aarch64", target_arch = "x86_64"), target_env = "gnu"),
    253                    target_os = "cygwin",
    254                ))] {
    255                /// personality fn called by [Windows Structured Exception Handling][windows-eh]
    256                ///
    257                /// On x86_64 and AArch64 MinGW targets, the unwinding mechanism is SEH,
    258                /// however the unwind handler data (aka LSDA) uses GCC-compatible encoding
    259                ///
    260                /// [windows-eh]: https://learn.microsoft.com/en-us/cpp/cpp/structured-exception-handling-c-cpp?view=msvc-170
    261                #[lang = "eh_personality"]
    262                #[allow(nonstandard_style)]
    263                unsafe extern "C" fn rust_eh_personality(
    264                    exceptionRecord: *mut uw::EXCEPTION_RECORD,
    265                    establisherFrame: uw::LPVOID,
    266                    contextRecord: *mut uw::CONTEXT,
    267                    dispatcherContext: *mut uw::DISPATCHER_CONTEXT,
    268                ) -> uw::EXCEPTION_DISPOSITION {
    269                    // SAFETY: the cfg is still target_os = "windows" and target_env = "gnu",
    270                    // which means that this is the correct function to call, passing our impl fn
    271                    // as the callback which gets actually used
    272                    unsafe {
    273                        uw::_GCC_specific_handler(
    274                            exceptionRecord,
    275                            establisherFrame,
    276                            contextRecord,
    277                            dispatcherContext,
    278                            rust_eh_personality_impl,
    279                        )
    280                    }
    281                }
    282            } else {
    283                /// personality fn called by [Itanium C++ ABI Exception Handling][itanium-eh]
    284                ///
    285                /// The personality routine for most non-Windows targets. This will be called by
    286                /// the unwinding library:
    287                /// - "In the search phase, the framework repeatedly calls the personality routine,
    288                ///   with the _UA_SEARCH_PHASE flag as described below, first for the current PC
    289                ///   and register state, and then unwinding a frame to a new PC at each step..."
    290                /// - "If the search phase reports success, the framework restarts in the cleanup
    291                ///    phase. Again, it repeatedly calls the personality routine, with the
    292                ///   _UA_CLEANUP_PHASE flag as described below, first for the current PC and
    293                ///   register state, and then unwinding a frame to a new PC at each step..."i
    294                ///
    295                /// [itanium-eh]: https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html
    296                #[lang = "eh_personality"]
    297                unsafe extern "C" fn rust_eh_personality(
    298                    version: c_int,
    299                    actions: uw::_Unwind_Action,
    300                    exception_class: uw::_Unwind_Exception_Class,
    301                    exception_object: *mut uw::_Unwind_Exception,
    302                    context: *mut uw::_Unwind_Context,
    303                ) -> uw::_Unwind_Reason_Code {
    304                    // SAFETY: the platform support must modify the cfg for the inner fn
    305                    // if it needs something different than what is currently invoked.
    306                    unsafe {
    307                        rust_eh_personality_impl(
    308                            version,
    309                            actions,
    310                            exception_class,
    311                            exception_object,
    312                            context,
    313                        )
    314                    }
    315                }
    316            }
    317        }
    318    }
    319}
    320
    321unsafe fn find_eh_action(context: *mut uw::_Unwind_Context) -> Result<EHAction, ()> {
    322    unsafe {
    323        let lsda = uw::_Unwind_GetLanguageSpecificData(context) as *const u8;
    324        let mut ip_before_instr: c_int = 0;
    325        let ip = uw::_Unwind_GetIPInfo(context, &mut ip_before_instr);
    326        let eh_context = EHContext {
    327            // The return address points 1 byte past the call instruction,
    328            // which could be in the next IP range in LSDA range table.
    329            //
    330            // `ip = -1` has special meaning, so use wrapping sub to allow for that
    331            ip: if ip_before_instr != 0 { ip } else { ip.wrapping_sub(1) },
    332            func_start: uw::_Unwind_GetRegionStart(context),
    333            get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
    334            get_data_start: &|| uw::_Unwind_GetDataRelBase(context),
    335        };
    336        eh::find_eh_action(lsda, &eh_context)
    337    }
    338}