llvm-project/libcxxabi/src/cxa_personality.cpp

//===------------------------- cxa_exception.cpp --------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//  
//  This file implements the "Exception Handling APIs"
//  http://www.codesourcery.com/public/cxx-abi/abi-eh.html
//  http://www.intel.com/design/itanium/downloads/245358.htm
//  
//===----------------------------------------------------------------------===//

#include "unwind.h"
#include "cxa_exception.hpp"
#include "cxa_handlers.hpp"
#include "private_typeinfo.h"
#include <typeinfo>
#include <stdlib.h>
#include <assert.h>

/*
    Exception Header Layout:

+---------------------------+-----------------------------+---------------+
| __cxa_exception           | _Unwind_Exception CLNGC++\0 | thrown object |
+---------------------------+-----------------------------+---------------+
                                                          ^
                                                          |
  +-------------------------------------------------------+
  |
+---------------------------+-----------------------------+
| __cxa_dependent_exception | _Unwind_Exception CLNGC++\1 |
+---------------------------+-----------------------------+

    Exception Handling Table Layout:

+-----------------+--------+
| lpStartEncoding | (char) |
+---------+-------+--------+---------------+-----------------------+
| lpStart | (encoded wtih lpStartEncoding) | defaults to funcStart |
+---------+-----+--------+-----------------+---------------+-------+
| ttypeEncoding | (char) | Encoding of the type_info table |
+---------------+-+------+----+----------------------------+----------------+
| classInfoOffset | (ULEB128) | Offset to type_info table, defaults to null |
+-----------------++--------+-+----------------------------+----------------+
| callSiteEncoding | (char) | Encoding for Call Site Table |
+------------------+--+-----+-----+------------------------+--------------------------+
| callSiteTableLength | (ULEB128) | Call Site Table length, used to find Action table |
+---------------------+-----------+------------------------------------------------+--+
| Beginning of Call Site Table            If the current ip lies within the        |
| ...                                     (start, length) range of one of these    |
|                                         call sites, there may be action needed.  |
| +-------------+---------------------------------+------------------------------+ |
| | start       | (encoded with callSiteEncoding) | offset relative to funcStart | |
| | length      | (encoded with callSiteEncoding) | lenght of code fragment      | |
| | landingPad  | (encoded with callSiteEncoding) | offset relative to lpStart   | |
| | actionEntry | (ULEB128)                       | Action Table Index 1-based   | |
| |             |                                 | actionEntry == 0 -> cleanup  | |
| +-------------+---------------------------------+------------------------------+ |
| ...                                                                              |
+---------------------------------------------------------------------+------------+
| Beginning of Action Table       ttypeIndex == 0 : cleanup           |
| ...                             ttypeIndex  > 0 : catch             |
|                                 ttypeIndex  < 0 : exception spec    |
| +--------------+-----------+--------------------------------------+ |
| | ttypeIndex   | (SLEB128) | Index into type_info Table (1-based) | |
| | actionOffset | (SLEB128) | Offset into next Action Table entry  | |
| +--------------+-----------+--------------------------------------+ |
| ...                                                                 |
+---------------------------------------------------------------------+-----------------+
| type_info Table, but classInfoOffset does *not* point here!                           |
| +----------------+------------------------------------------------+-----------------+ |
| | Nth type_info* | Encoded with ttypeEncoding, 0 means catch(...) | ttypeIndex == N | |
| +----------------+------------------------------------------------+-----------------+ |
| ...                                                                                   |
| +----------------+------------------------------------------------+-----------------+ |
| | 1st type_info* | Encoded with ttypeEncoding, 0 means catch(...) | ttypeIndex == 1 | |
| +----------------+------------------------------------------------+-----------------+ |
| +---------------------------------------+-----------+------------------------------+  |
| | 1st ttypeIndex for 1st exception spec | (ULEB128) | classInfoOffset points here! |  |
| | ...                                   | (ULEB128) |                              |  |
| | Mth ttypeIndex for 1st exception spec | (ULEB128) |                              |  |
| | 0                                     | (ULEB128) |                              |  |
| +---------------------------------------+------------------------------------------+  |
| ...                                                                                   |
| +---------------------------------------+------------------------------------------+  |
| | 0                                     | (ULEB128) | throw()                      |  |
| +---------------------------------------+------------------------------------------+  |
| ...                                                                                   |
| +---------------------------------------+------------------------------------------+  |
| | 1st ttypeIndex for Nth exception spec | (ULEB128) |                              |  |
| | ...                                   | (ULEB128) |                              |  |
| | Mth ttypeIndex for Nth exception spec | (ULEB128) |                              |  |
| | 0                                     | (ULEB128) |                              |  |
| +---------------------------------------+------------------------------------------+  |
+---------------------------------------------------------------------------------------+

Notes:

*  ttypeIndex in the Action Table, and in the exception spec table, is an index,
     not a byte count, if positive.  It is a negative index offset of
     classInfoOffset and the sizeof entry depends on ttypeEncoding.
   But if ttypeIndex is negative, it is a positive 1-based byte offset into the
     type_info Table.
   And if ttypeIndex is zero, it refers to a catch (...).

*  landingPad can be 0, this implies there is nothing to be done.

*  landingPad != 0 and actionEntry == 0 implies a cleanup needs to be done
     @landingPad.

*  A cleanup can also be found under landingPad != 0 and actionEntry != 0 in
     the Action Table with ttypeIndex == 0.
*/

namespace __cxxabiv1
{

extern "C"
{

// private API

// Heavily borrowed from llvm/examples/ExceptionDemo/ExceptionDemo.cpp

// DWARF Constants
enum
{
    DW_EH_PE_absptr   = 0x00,
    DW_EH_PE_uleb128  = 0x01,
    DW_EH_PE_udata2   = 0x02,
    DW_EH_PE_udata4   = 0x03,
    DW_EH_PE_udata8   = 0x04,
    DW_EH_PE_sleb128  = 0x09,
    DW_EH_PE_sdata2   = 0x0A,
    DW_EH_PE_sdata4   = 0x0B,
    DW_EH_PE_sdata8   = 0x0C,
    DW_EH_PE_pcrel    = 0x10,
    DW_EH_PE_textrel  = 0x20,
    DW_EH_PE_datarel  = 0x30,
    DW_EH_PE_funcrel  = 0x40,
    DW_EH_PE_aligned  = 0x50,
    DW_EH_PE_indirect = 0x80,
    DW_EH_PE_omit     = 0xFF
};

/// Read a uleb128 encoded value and advance pointer 
/// See Variable Length Data Appendix C in: 
/// @link http://dwarfstd.org/Dwarf4.pdf @unlink
/// @param data reference variable holding memory pointer to decode from
/// @returns decoded value
static
uintptr_t
readULEB128(const uint8_t** data)
{
    uintptr_t result = 0;
    uintptr_t shift = 0;
    unsigned char byte;
    const uint8_t *p = *data;
    do
    {
        byte = *p++;
        result |= static_cast<uintptr_t>(byte & 0x7F) << shift;
        shift += 7;
    } while (byte & 0x80);
    *data = p;
    return result;
}

/// Read a sleb128 encoded value and advance pointer 
/// See Variable Length Data Applendix C in: 
/// @link http://dwarfstd.org/Dwarf4.pdf @unlink
/// @param data reference variable holding memory pointer to decode from
/// @returns decoded value
static
uintptr_t
readSLEB128(const uint8_t** data)
{
    uintptr_t result = 0;
    uintptr_t shift = 0;
    unsigned char byte;
    const uint8_t *p = *data;
    do
    {
        byte = *p++;
        result |= static_cast<uintptr_t>(byte & 0x7F) << shift;
        shift += 7;
    } while (byte & 0x80);
    *data = p;
    if ((byte & 0x40) && (shift < (sizeof(result) << 3)))
        result |= static_cast<uintptr_t>(~0) << shift;
    return result;
}

/// Read a pointer encoded value and advance pointer 
/// See Variable Length Data in: 
/// @link http://dwarfstd.org/Dwarf3.pdf @unlink
/// @param data reference variable holding memory pointer to decode from
/// @param encoding dwarf encoding type
/// @returns decoded value
static
uintptr_t
readEncodedPointer(const uint8_t** data, uint8_t encoding)
{
    uintptr_t result = 0;
    if (encoding == DW_EH_PE_omit) 
        return result;
    const uint8_t* p = *data;
    // first get value 
    switch (encoding & 0x0F)
    {
    case DW_EH_PE_absptr:
        result = *((uintptr_t*)p);
        p += sizeof(uintptr_t);
        break;
    case DW_EH_PE_uleb128:
        result = readULEB128(&p);
        break;
    case DW_EH_PE_sleb128:
        result = readSLEB128(&p);
        break;
    case DW_EH_PE_udata2:
        result = *((uint16_t*)p);
        p += sizeof(uint16_t);
        break;
    case DW_EH_PE_udata4:
        result = *((uint32_t*)p);
        p += sizeof(uint32_t);
        break;
    case DW_EH_PE_udata8:
        result = *((uint64_t*)p);
        p += sizeof(uint64_t);
        break;
    case DW_EH_PE_sdata2:
        result = *((int16_t*)p);
        p += sizeof(int16_t);
        break;
    case DW_EH_PE_sdata4:
        result = *((int32_t*)p);
        p += sizeof(int32_t);
        break;
    case DW_EH_PE_sdata8:
        result = *((int64_t*)p);
        p += sizeof(int64_t);
        break;
    default:
        // not supported 
        abort();
        break;
    }
    // then add relative offset 
    switch (encoding & 0x70)
    {
    case DW_EH_PE_absptr:
        // do nothing 
        break;
    case DW_EH_PE_pcrel:
        if (result)
            result += (uintptr_t)(*data);
        break;
    case DW_EH_PE_textrel:
    case DW_EH_PE_datarel:
    case DW_EH_PE_funcrel:
    case DW_EH_PE_aligned:
    default:
        // not supported 
        abort();
        break;
    }
    // then apply indirection 
    if (result && (encoding & DW_EH_PE_indirect))
        result = *((uintptr_t*)result);
    *data = p;
    return result;
}

static
void
call_terminate(bool native_exception, _Unwind_Exception* unwind_exception)
{
    __cxa_begin_catch(unwind_exception);
    if (native_exception)
    {
        // Use the stored terminate_handler if possible
        __cxa_exception* exception_header = (__cxa_exception*)(unwind_exception+1) - 1;
        std::__terminate(exception_header->terminateHandler);
    }
    std::terminate();
}

static
const __shim_type_info*
get_shim_type_info(int64_t ttypeIndex, const uint8_t* classInfo,
                   uint8_t ttypeEncoding, bool native_exception,
                   _Unwind_Exception* unwind_exception)
{
    // TODO:  Move this check sooner
    if (classInfo == 0)
    {
        // this should not happen
        call_terminate(native_exception, unwind_exception);
    }
    switch (ttypeEncoding & 0x0F)
    {
    case DW_EH_PE_absptr:
        ttypeIndex *= sizeof(void*);
        break;
    case DW_EH_PE_udata2:
    case DW_EH_PE_sdata2:
        ttypeIndex *= 2;
        break;
    case DW_EH_PE_udata4:
    case DW_EH_PE_sdata4:
        ttypeIndex *= 4;
        break;
    case DW_EH_PE_udata8:
    case DW_EH_PE_sdata8:
        ttypeIndex *= 8;
        break;
    default:
        // TODO:  Move this check sooner
        // this should not happen
        call_terminate(native_exception, unwind_exception);
    }
    classInfo -= ttypeIndex;
    return (const __shim_type_info*)readEncodedPointer(&classInfo, ttypeEncoding);
}

static
bool
exception_spec_can_catch(int64_t specIndex, const uint8_t* classInfo,
                         uint8_t ttypeEncoding, const __shim_type_info* excpType,
                         void* adjustedPtr, _Unwind_Exception* unwind_exception)
{
    // TODO:  Move this check sooner
    if (classInfo == 0)
    {
        // this should not happen
        call_terminate(false, unwind_exception);
    }
    // specIndex is negative of 1-based byte offset into classInfo;
    specIndex = -specIndex;
    --specIndex;
    const uint8_t* temp = classInfo + specIndex;
    // If any type in the spec list can catch excpType, return false, else return true
    //    adjustments to adjustedPtr are ignored.
    while (true)
    {
        uint64_t ttypeIndex = readULEB128(&temp);
        if (ttypeIndex == 0)
            break;
        const __shim_type_info* catchType = get_shim_type_info(ttypeIndex,
                                                               classInfo,
                                                               ttypeEncoding,
                                                               true,
                                                               unwind_exception);
        void* tempPtr = adjustedPtr;
        if (catchType->can_catch(excpType, tempPtr))
            return false;
    }
    return true;
}

static
void*
get_thrown_object_ptr(_Unwind_Exception* unwind_exception)
{
    // Even for foreign exceptions, the exception object is *probably* at unwind_exception + 1
    //    Regardless, this library is prohibited from touching a foreign exception
    void* adjustedPtr = unwind_exception + 1;
    if (unwind_exception->exception_class == kOurDependentExceptionClass)
        adjustedPtr = ((__cxa_dependent_exception*)adjustedPtr - 1)->primaryException;
    return adjustedPtr;
}

/*
    There are 3 types of scans needed:

    1.  Scan for handler with native or foreign exception.  If handler found,
        save state and return _URC_HANDLER_FOUND, else return _URC_CONTINUE_UNWIND.
        May also report an error on invalid input.
        May terminate for invalid exception table.
        _UA_SEARCH_PHASE

    2.  Scan for handler with foreign exception.  Must return _URC_HANDLER_FOUND,
        or call terminate.
        _UA_CLEANUP_PHASE && _UA_HANDLER_FRAME && !native_exception

    3.  Scan for cleanups.  If a handler is found and this isn't forced unwind,
        then terminate, otherwise ignore the handler and keep looking for cleanup.
        If a cleanup is found, return _URC_HANDLER_FOUND, else return _URC_CONTINUE_UNWIND.
        May also report an error on invalid input.
        May terminate for invalid exception table.
        _UA_CLEANUP_PHASE && !_UA_HANDLER_FRAME
*/

namespace
{

struct scan_results
{
    int64_t        ttypeIndex;   // > 0 catch handler, < 0 exception spec handler, == 0 a cleanup
    const uint8_t* actionRecord;         // Currently unused.  TODO: Remove?
    const uint8_t* languageSpecificData;  // Needed only for __cxa_call_unexpected
    uintptr_t      landingPad;   // null -> nothing found, else something found
    void*          adjustedPtr;  // Used in cxa_exception.cpp
    _Unwind_Reason_Code reason;  // One of _URC_FATAL_PHASE1_ERROR,
                                 //        _URC_FATAL_PHASE2_ERROR,
                                 //        _URC_CONTINUE_UNWIND,
                                 //        _URC_HANDLER_FOUND
};

}  // unnamed namespace

static
void
scan_eh_tab(scan_results& results, _Unwind_Action actions, bool native_exception,
            _Unwind_Exception* unwind_exception, _Unwind_Context* context)
{
    // Initialize results to found nothing but an error
    results.ttypeIndex = 0;
    results.actionRecord = 0;
    results.languageSpecificData = 0;
    results.landingPad = 0;
    results.adjustedPtr = 0;
    results.reason = _URC_FATAL_PHASE1_ERROR;
    // Check for consistent actions
    if (actions & _UA_SEARCH_PHASE)
    {
        // Do Phase 1
        if (actions & (_UA_CLEANUP_PHASE | _UA_HANDLER_FRAME | _UA_FORCE_UNWIND))
        {
            // None of these flags should be set during Phase 1
            //   Client error
            results.reason = _URC_FATAL_PHASE1_ERROR;
            return;
        }
    }
    else if (actions & _UA_CLEANUP_PHASE)
    {
        if ((actions & _UA_HANDLER_FRAME) && (actions & _UA_FORCE_UNWIND))
        {
            // _UA_HANDLER_FRAME should only be set if phase 1 found a handler.
            // If _UA_FORCE_UNWIND is set, phase 1 shouldn't have happened.
            //    Client error
            results.reason = _URC_FATAL_PHASE2_ERROR;
            return;
        }
    }
    else // Niether _UA_SEARCH_PHASE nor _UA_CLEANUP_PHASE is set
    {
        // One of these should be set.
        //   Client error
        results.reason = _URC_FATAL_PHASE1_ERROR;
        return;
    }
    // Start scan by getting exception table address
    const uint8_t* lsda = (const uint8_t*)_Unwind_GetLanguageSpecificData(context);
    if (lsda == 0)
    {
        // There is no exception table
        results.reason = _URC_CONTINUE_UNWIND;
        return;
    }
    results.languageSpecificData = lsda;
    // Get the current instruction pointer and offset it before next
    // instruction in the current frame which threw the exception.
    uintptr_t ip = _Unwind_GetIP(context) - 1;
    // Get beginning current frame's code (as defined by the 
    // emitted dwarf code)
    uintptr_t funcStart = _Unwind_GetRegionStart(context);
    uintptr_t ipOffset = ip - funcStart;
    const uint8_t* classInfo = NULL;
    // Note: See JITDwarfEmitter::EmitExceptionTable(...) for corresponding
    //       dwarf emission
    // Parse LSDA header.
    uint8_t lpStartEncoding = *lsda++;
    const uint8_t* lpStart = (const uint8_t*)readEncodedPointer(&lsda, lpStartEncoding);
    if (lpStart == 0)
        lpStart = (const uint8_t*)funcStart;
    uint8_t ttypeEncoding = *lsda++;
    if (ttypeEncoding != DW_EH_PE_omit)
    {
        // Calculate type info locations in emitted dwarf code which
        // were flagged by type info arguments to llvm.eh.selector
        // intrinsic
        uintptr_t classInfoOffset = readULEB128(&lsda);
        classInfo = lsda + classInfoOffset;
    }
    // Walk call-site table looking for range that 
    // includes current PC. 
    uint8_t callSiteEncoding = *lsda++;
    uint32_t callSiteTableLength = readULEB128(&lsda);
    const uint8_t* callSiteTableStart = lsda;
    const uint8_t* callSiteTableEnd = callSiteTableStart + callSiteTableLength;
    const uint8_t* actionTableStart = callSiteTableEnd;
    const uint8_t* callSitePtr = callSiteTableStart;
    while (true)
    {
        // There is one entry per call site.
        // The call sites are non-overlapping in [start, start+length)
        // The call sites are ordered in increasing value of start
        uintptr_t start = readEncodedPointer(&callSitePtr, callSiteEncoding);
        uintptr_t length = readEncodedPointer(&callSitePtr, callSiteEncoding);
        uintptr_t landingPad = readEncodedPointer(&callSitePtr, callSiteEncoding);
        uintptr_t actionEntry = readULEB128(&callSitePtr);
        if ((start <= ipOffset) && (ipOffset < (start + length)))
        {
            // Found the call site containing ip.
            if (landingPad == 0)
            {
                // No handler here
                results.reason = _URC_CONTINUE_UNWIND;
                return;
            }
            landingPad = (uintptr_t)lpStart + landingPad;
            if (actionEntry == 0)
            {
                // Found a cleanup
                // If this is a type 1 or type 2 search, there are no handlers
                // If this is a type 3 search, you want to install the cleanup.
                if ((actions & _UA_CLEANUP_PHASE) && !(actions & _UA_HANDLER_FRAME))
                {
                    results.ttypeIndex = 0;  // Redundant but clarifying
                    results.landingPad = landingPad;
                    results.reason = _URC_HANDLER_FOUND;
                    return;
                }
                // No handler here
                results.reason = _URC_CONTINUE_UNWIND;
                return;
            }
            // Convert 1-based byte offset into
            const uint8_t* action = actionTableStart + (actionEntry - 1);
            // Scan action entries until you find a matching handler, cleanup, or the end of action list
            while (true)
            {
                const uint8_t* actionRecord = action;
                int64_t ttypeIndex = readSLEB128(&action);
                if (ttypeIndex > 0)
                {
                    // Found a catch, does it actually catch?
                    // First check for catch (...)
                    const __shim_type_info* catchType =
                        get_shim_type_info(ttypeIndex, classInfo,
                                           ttypeEncoding, native_exception,
                                           unwind_exception);
                    if (catchType == 0)
                    {
                        // Found catch (...) catches everything, including foreign exceptions
                        // If this is a type 1 search save state and return _URC_HANDLER_FOUND
                        // If this is a type 2 search save state and return _URC_HANDLER_FOUND
                        // If this is a type 3 search !_UA_FORCE_UNWIND, we should have found this in phase 1!
                        // If this is a type 3 search _UA_FORCE_UNWIND, ignore handler and continue scan
                        if ((actions & _UA_SEARCH_PHASE) || (actions & _UA_HANDLER_FRAME))
                        {
                            // Save state and return _URC_HANDLER_FOUND
                            results.ttypeIndex = ttypeIndex;
                            results.actionRecord = actionRecord;
                            results.landingPad = landingPad;
                            results.adjustedPtr = get_thrown_object_ptr(unwind_exception);
                            results.reason = _URC_HANDLER_FOUND;
                            return;
                        }
                        else if (!(actions & _UA_FORCE_UNWIND))
                        {
                            // It looks like the exception table has changed
                            //    on us.  Likely stack corruption!
                            call_terminate(native_exception, unwind_exception);
                        }
                    }
                    // Else this is a catch (T) clause and will never
                    //    catch a foreign exception
                    else if (native_exception)
                    {
                        __cxa_exception* exception_header = (__cxa_exception*)(unwind_exception+1) - 1;
                        void* adjustedPtr = get_thrown_object_ptr(unwind_exception);
                        const __shim_type_info* excpType =
                            static_cast<const __shim_type_info*>(exception_header->exceptionType);
                        if (adjustedPtr == 0 || excpType == 0)
                        {
                            // Something very bad happened
                            call_terminate(native_exception, unwind_exception);
                        }
                        if (catchType->can_catch(excpType, adjustedPtr))
                        {
                            // Found a matching handler
                            // If this is a type 1 search save state and return _URC_HANDLER_FOUND
                            // If this is a type 3 search and !_UA_FORCE_UNWIND, we should have found this in phase 1!
                            // If this is a type 3 search and _UA_FORCE_UNWIND, ignore handler and continue scan
                            if (actions & _UA_SEARCH_PHASE)
                            {
                                // Save state and return _URC_HANDLER_FOUND
                                results.ttypeIndex = ttypeIndex;
                                results.actionRecord = actionRecord;
                                results.landingPad = landingPad;
                                results.adjustedPtr = adjustedPtr;
                                results.reason = _URC_HANDLER_FOUND;
                                return;
                            }
                            else if (!(actions & _UA_FORCE_UNWIND))
                            {
                                // It looks like the exception table has changed
                                //    on us.  Likely stack corruption!
                                call_terminate(native_exception, unwind_exception);
                            }
                        }
                    }
                    // Scan next action ...
                }
                else if (ttypeIndex < 0)
                {
                    // Found an exception spec.  If this is a foreign exception,
                    //   it is always caught.
                    if (native_exception)
                    {
                        // Does the exception spec catch this native exception?
                        __cxa_exception* exception_header = (__cxa_exception*)(unwind_exception+1) - 1;
                        void* adjustedPtr = get_thrown_object_ptr(unwind_exception);
                        const __shim_type_info* excpType =
                            static_cast<const __shim_type_info*>(exception_header->exceptionType);
                        if (adjustedPtr == 0 || excpType == 0)
                        {
                            // Something very bad happened
                            call_terminate(native_exception, unwind_exception);
                        }
                        if (exception_spec_can_catch(ttypeIndex, classInfo,
                                                     ttypeEncoding, excpType,
                                                     adjustedPtr, unwind_exception))
                        {
                            // native exception caught by exception spec
                            // If this is a type 1 search, save state and return _URC_HANDLER_FOUND
                            // If this is a type 3 search !_UA_FORCE_UNWIND, we should have found this in phase 1!
                            // If this is a type 3 search _UA_FORCE_UNWIND, ignore handler and continue scan
                            if (actions & _UA_SEARCH_PHASE)
                            {
                                // Save state and return _URC_HANDLER_FOUND
                                results.ttypeIndex = ttypeIndex;
                                results.actionRecord = actionRecord;
                                results.landingPad = landingPad;
                                results.adjustedPtr = adjustedPtr;
                                results.reason = _URC_HANDLER_FOUND;
                                return;
                            }
                            else if (!(actions & _UA_FORCE_UNWIND))
                            {
                                // It looks like the exception table has changed
                                //    on us.  Likely stack corruption!
                                call_terminate(native_exception, unwind_exception);
                            }
                        }
                    }
                    else
                    {
                        // foreign exception caught by exception spec
                        // If this is a type 1 search, save state and return _URC_HANDLER_FOUND
                        // If this is a type 2 search, save state and return _URC_HANDLER_FOUND
                        // If this is a type 3 search !_UA_FORCE_UNWIND, we should have found this in phase 1!
                        // If this is a type 3 search _UA_FORCE_UNWIND, ignore handler and continue scan
                        if ((actions & _UA_SEARCH_PHASE) || (actions & _UA_HANDLER_FRAME))
                        {
                            // Save state and return _URC_HANDLER_FOUND
                            results.ttypeIndex = ttypeIndex;
                            results.actionRecord = actionRecord;
                            results.landingPad = landingPad;
                            results.adjustedPtr = get_thrown_object_ptr(unwind_exception);
                            results.reason = _URC_HANDLER_FOUND;
                            return;
                        }
                        else if (!(actions & _UA_FORCE_UNWIND))
                        {
                            // It looks like the exception table has changed
                            //    on us.  Likely stack corruption!
                            call_terminate(native_exception, unwind_exception);
                        }
                    }
                    // Scan next action ...
                }
                else  // ttypeIndex == 0
                {
                    // Found a cleanup
                    // If this is a type 1 search, ignore it and continue scan
                    // If this is a type 2 search, ignore it and continue scan
                    // If this is a type 3 search, save state and return _URC_HANDLER_FOUND
                    if ((actions & _UA_CLEANUP_PHASE) && !(actions & _UA_HANDLER_FRAME))
                    {
                        // Save state and return _URC_HANDLER_FOUND
                        results.ttypeIndex = ttypeIndex;
                        results.actionRecord = actionRecord;
                        results.landingPad = landingPad;
                        results.adjustedPtr = get_thrown_object_ptr(unwind_exception);
                        results.reason = _URC_HANDLER_FOUND;
                        return;
                    }
                }
                const uint8_t* temp = action;
                int64_t actionOffset = readSLEB128(&temp);
                if (actionOffset == 0)
                {
                    // End of action list, no matching handler or cleanup found
                    // If this is a type 2 search, phase 1 told us we would find
                    //   a handler and we didn't.  Something has gone terribly wrong.
                    // Searches type 1 and 3 should return _URC_CONTINUE_UNWIND
                    if (actions & _UA_HANDLER_FRAME)
                        call_terminate(native_exception, unwind_exception);
                    results.reason = _URC_CONTINUE_UNWIND;
                    return;
                }
                // Go to next action
                action += actionOffset;
            }  // there is no break out of this loop, only return
        }
        else if (ipOffset < start)
        {
            // There is no call site for this ip
            // Something bad has happened.  We should never get here.
            // Possible stack corruption.
            call_terminate(native_exception, unwind_exception);
        }
    }  // there is no break out of this loop, only return
}

// public API

/*
A foreign exception is defined by by one with an exceptionClass that doesn't
have 'C++' in the 3 low order bytes 3 - 1:

  big end  |   | ... | C | + | + |1/0|  little end

The lowest order byte may be 0 or 1.

The personality function branches on actions like so:

_UA_SEARCH_PHASE

    If _UA_CLEANUP_PHASE or _UA_HANDLER_FRAME or _UA_FORCE_UNWIND there's
      an error from above, return _URC_FATAL_PHASE1_ERROR.

    Scan for anything that could stop unwinding:

       1.  A catch clause that will catch this exception
           (will never catch foreign).
       2.  A catch (...) (will always catch foreign).
       3.  An exception spec that will catch this exception
           (will always catch foreign).
    If a handler is found
        If not foreign
            Save state in header
        return _URC_HANDLER_FOUND
    Else a handler not found
        return _URC_CONTINUE_UNWIND

_UA_CLEANUP_PHASE

    If _UA_HANDLER_FRAME
        If _UA_FORCE_UNWIND
            How did this happen?  return _URC_FATAL_PHASE2_ERROR
        If foreign
            Do _UA_SEARCH_PHASE to recover state
        else
            Recover state from header
        Transfer control to landing pad.  return _URC_INSTALL_CONTEXT
    
    Else
    
        Scan for anything that can not stop unwinding:
    
            1.  A cleanup.
        
        If a cleanup is found
            transfer control to it. return _URC_INSTALL_CONTEXT
        Else a cleanup is not found: return _URC_CONTINUE_UNWIND
*/

_Unwind_Reason_Code
__gxx_personality_v0(int version, _Unwind_Action actions, uint64_t exceptionClass,
                     _Unwind_Exception* unwind_exception, _Unwind_Context* context)
{
    if (version != 1 || unwind_exception == 0 || context == 0)
        return _URC_FATAL_PHASE1_ERROR;
    bool native_exception = (exceptionClass     & get_language) ==
                            (kOurExceptionClass & get_language);
    scan_results results;
    if (actions & _UA_SEARCH_PHASE)
    {
        scan_eh_tab(results, actions, native_exception, unwind_exception, context);
        if (results.reason == _URC_HANDLER_FOUND)
        {
            if (native_exception)
            {
                __cxa_exception* exception_header = (__cxa_exception*)(unwind_exception+1) - 1;
                exception_header->handlerSwitchValue = static_cast<int>(results.ttypeIndex);
                exception_header->actionRecord = results.actionRecord;
                exception_header->languageSpecificData = results.languageSpecificData;
                exception_header->catchTemp = reinterpret_cast<void*>(results.landingPad);
                exception_header->adjustedPtr = results.adjustedPtr;
            }
            return _URC_HANDLER_FOUND;
        }
        return results.reason;
    }
    if (actions & _UA_CLEANUP_PHASE)
    {
        if (actions & _UA_HANDLER_FRAME)
        {
            if (native_exception)
            {
                __cxa_exception* exception_header = (__cxa_exception*)(unwind_exception+1) - 1;
                results.ttypeIndex = exception_header->handlerSwitchValue;
                results.actionRecord = exception_header->actionRecord;
                results.languageSpecificData = exception_header->languageSpecificData;
                results.landingPad = reinterpret_cast<uintptr_t>(exception_header->catchTemp);
                results.adjustedPtr = exception_header->adjustedPtr;
            }
            else
            {
                scan_eh_tab(results, actions, native_exception, unwind_exception, context);
            }
            _Unwind_SetGR(context, __builtin_eh_return_data_regno(0), (uintptr_t)unwind_exception);
            _Unwind_SetGR(context, __builtin_eh_return_data_regno(1), results.ttypeIndex);
            _Unwind_SetIP(context, results.landingPad);
            return _URC_INSTALL_CONTEXT;
        }
        scan_eh_tab(results, actions, native_exception, unwind_exception, context);
        if (results.reason == _URC_HANDLER_FOUND)
        {
            _Unwind_SetGR(context, __builtin_eh_return_data_regno(0), (uintptr_t)unwind_exception);
            _Unwind_SetGR(context, __builtin_eh_return_data_regno(1), results.ttypeIndex);
            _Unwind_SetIP(context, results.landingPad);
            return _URC_INSTALL_CONTEXT;
        }
        return results.reason;
    }
    // Neither _UA_SEARCH_PHASE nor _UA_CLEANUP_PHASE
    return _URC_FATAL_PHASE1_ERROR;
}

__attribute__((noreturn))
void
__cxa_call_unexpected(void* arg)
{
    _Unwind_Exception* unwind_exception = static_cast<_Unwind_Exception*>(arg);
    if (unwind_exception == 0)
        call_terminate(false, unwind_exception);
    __cxa_begin_catch(unwind_exception);
    bool native_old_exception = (unwind_exception->exception_class & get_language) ==
                                (kOurExceptionClass                & get_language);
    std::unexpected_handler u_handler;
    std::terminate_handler t_handler;
    __cxa_exception* old_exception_header = 0;
    if (native_old_exception)
    {
        old_exception_header = (__cxa_exception*)(unwind_exception+1) - 1;
        t_handler = old_exception_header->terminateHandler;
        u_handler = old_exception_header->unexpectedHandler;
    }
    else
    {
        t_handler = std::get_terminate();
        u_handler = std::get_unexpected();
    }
    try
    {
        std::__unexpected(u_handler);
    }
    catch (...)
    {
        // If the old exception is foreign, then all we can do is terminate.
        //   We have no way to recover the needed old exception spec.  There's
        //   no way to pass that information here.  And the personality routine
        //   can't call us directly and do anything but terminate() if we throw
        //   from here.
        if (native_old_exception)
        {
            int64_t ttypeIndex = old_exception_header->handlerSwitchValue;
            // Have:
            //   old_exception_header->languageSpecificData
            //   old_exception_header->actionRecord
            // Need
            //   const uint8_t* classInfo
            //   uint8_t ttypeEncoding
            const uint8_t* lsda = old_exception_header->languageSpecificData;
            uint8_t lpStartEncoding = *lsda++;
            const uint8_t* lpStart = (const uint8_t*)readEncodedPointer(&lsda, lpStartEncoding);
            uint8_t ttypeEncoding = *lsda++;
            if (ttypeEncoding == DW_EH_PE_omit)
                std::__terminate(t_handler);
            uintptr_t classInfoOffset = readULEB128(&lsda);
            const uint8_t* classInfo = lsda + classInfoOffset;
            // Is this new exception catchable by the exception spec at ttypeIndex?
            // The answer is obviously yes if the new and old exceptions are the same exception
            // If no
            //    throw;
            __cxa_eh_globals* globals = __cxa_get_globals_fast();
            __cxa_exception* new_exception_header = globals->caughtExceptions;
            if (new_exception_header == 0)
                // This shouldn't be able to happen!
                std::__terminate(t_handler);
            bool native_new_exception =
                (new_exception_header->unwindHeader.exception_class & get_language) ==
                                                (kOurExceptionClass & get_language);
            void* adjustedPtr;
            if (native_new_exception && new_exception_header != old_exception_header)
            {
                const __shim_type_info* excpType =
                    static_cast<const __shim_type_info*>(new_exception_header->exceptionType);
                adjustedPtr =
                    new_exception_header->unwindHeader.exception_class == kOurDependentExceptionClass ?
                        ((__cxa_dependent_exception*)new_exception_header)->primaryException :
                        new_exception_header + 1;
                if (!exception_spec_can_catch(ttypeIndex, classInfo, ttypeEncoding,
                                              excpType, adjustedPtr, unwind_exception))
                {
                    // We need to __cxa_end_catch, but for the old exception,
                    //   not the new one.  This is a little tricky ...
                    // Disguise new_exception_header as a rethrown exception, but
                    //   don't actually rethrow it.  This means you can temporarily
                    //   end the catch clause enclosing new_exception_header without
                    //   __cxa_end_catch destroying new_exception_header.
                    new_exception_header->handlerCount = -new_exception_header->handlerCount;
                    globals->uncaughtExceptions += 1;
                    // Call __cxa_end_catch for new_exception_header
                    __cxa_end_catch();
                    // Call __cxa_end_catch for old_exception_header
                    __cxa_end_catch();
                    // Renter this catch clause with new_exception_header
                    __cxa_begin_catch(&new_exception_header->unwindHeader);
                    // Rethrow new_exception_header
                    throw;
                }
            }
            // Will a std::bad_exception be catchable by the exception spec at
            //   ttypeIndex?
            // If no
            //    throw std::bad_exception();
            const __shim_type_info* excpType =
                static_cast<const __shim_type_info*>(&typeid(std::bad_exception));
            std::bad_exception be;
            adjustedPtr = &be;
            if (!exception_spec_can_catch(ttypeIndex, classInfo, ttypeEncoding,
                                          excpType, adjustedPtr, unwind_exception))
            {
                // We need to __cxa_end_catch for both the old exception and the
                //   new exception.  Technically we should do it in that order.
                //   But it is expedent to do it in the opposite order:
                // Call __cxa_end_catch for new_exception_header
                __cxa_end_catch();
                // Throw std::bad_exception will __cxa_end_catch for
                //   old_exception_header
                throw be;
            }
        }
    }
    std::__terminate(t_handler);
}

}  // extern "C"

}  // __cxxabiv1