unwind-cxx.h

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// -*- C++ -*- Exception handling and frame unwind runtime interface routines.
// Copyright (C) 2001 Free Software Foundation, Inc.
//
// This file is part of GCC.
//
// GCC is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2, or (at your option)
// any later version.
//
// GCC is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with GCC; see the file COPYING.  If not, write to
// the Free Software Foundation, 51 Franklin Street, Fifth Floor,
// Boston, MA 02110-1301, USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

// This is derived from the C++ ABI for IA-64.  Where we diverge
// for cross-architecture compatibility are noted with "@@@".

#ifndef _UNWIND_CXX_H
#define _UNWIND_CXX_H 1

// Level 2: C++ ABI

#include <typeinfo>
#include <exception>

#include <stddef.h>
#include "unwind.h"


typedef unsigned _Unwind_Word __attribute__((__mode__(__word__)));
typedef signed   _Unwind_Sword __attribute__((__mode__(__word__)));
typedef unsigned _Unwind_Word __attribute__((__mode__(__word__)));
typedef unsigned _Unwind_Ptr __attribute__((__mode__(__pointer__)));
typedef unsigned _Unwind_Exception_Class __attribute__((__mode__(__DI__)));
typedef unsigned _Unwind_Internal_Ptr __attribute__((__mode__(__pointer__)));

#pragma GCC visibility push(default)

namespace __cxxabiv1
{

// A C++ exception object consists of a header, which is a wrapper around
// an unwind object header with additional C++ specific information,
// followed by the exception object itself.

struct __cxa_exception
{
#if __LP64__
#if 0
    // This is a new field added with LLVM 10
    // <https://github.com/llvm/llvm-project/commit/674ec1eb16678b8addc02a4b0534ab383d22fa77>
    // "[libcxxabi] Insert padding in __cxa_exception struct for compatibility".  The HACK in
    // fillUnoException (bridges/source/cpp_uno/gcc3_macosx_x86-64/except.cxx) tries to find out at
    // runtime whether a __cxa_exception has this member.  Once we can be sure that we only run
    // against new libcxxabi that has this member, we can drop the "#if 0" here and drop the hack
    // in fillUnoException.

    // Now _Unwind_Exception is marked with __attribute__((aligned)),
    // which implies __cxa_exception is also aligned. Insert padding
    // in the beginning of the struct, rather than before unwindHeader.
    void *reserve;
#endif

    // This is a new field to support C++ 0x exception_ptr.
    // For binary compatibility it is at the start of this
    // struct which is prepended to the object thrown in
    // __cxa_allocate_exception.
  size_t referenceCount;
#endif
  // Manage the exception object itself.
  std::type_info *exceptionType;
  void (*exceptionDestructor)(void *); 

  // The C++ standard has entertaining rules wrt calling set_terminate
  // and set_unexpected in the middle of the exception cleanup process.
  void (*unexpectedHandler)(); // std::unexpected_handler dropped from C++17
  std::terminate_handler terminateHandler;

  // The caught exception stack threads through here.
  __cxa_exception *nextException;

  // How many nested handlers have caught this exception.  A negated
  // value is a signal that this object has been rethrown.
  int handlerCount;

#ifdef __ARM_EABI_UNWINDER__
  // Stack of exceptions in cleanups.
  __cxa_exception* nextPropagatingException;

  // The number of active cleanup handlers for this exception.
  int propagationCount;
#else
  // Cache parsed handler data from the personality routine Phase 1
  // for Phase 2 and __cxa_call_unexpected.
  int handlerSwitchValue;
  const unsigned char *actionRecord;
  const unsigned char *languageSpecificData;
  _Unwind_Ptr catchTemp;
  void *adjustedPtr;
#endif
#if !__LP64__
    // This is a new field to support C++ 0x exception_ptr.
    // For binary compatibility it is placed where the compiler
    // previously adding padded to 64-bit align unwindHeader.
  size_t referenceCount;
#endif

  // The generic exception header.  Must be last.
  _Unwind_Exception unwindHeader;
};

// Each thread in a C++ program has access to a __cxa_eh_globals object.
struct __cxa_eh_globals
{
  __cxa_exception *caughtExceptions;
  unsigned int uncaughtExceptions;
#ifdef __ARM_EABI_UNWINDER__
  __cxa_exception* propagatingExceptions;
#endif
};


// The __cxa_eh_globals for the current thread can be obtained by using
// either of the following functions.  The "fast" version assumes at least
// one prior call of __cxa_get_globals has been made from the current
// thread, so no initialization is necessary.
extern "C" __cxa_eh_globals *__cxa_get_globals () throw();
extern "C" __cxa_eh_globals *__cxa_get_globals_fast () throw();

// Allocate memory for the exception plus the thrown object.
extern "C" void *__cxa_allocate_exception(size_t thrown_size) throw();

// Free the space allocated for the exception.
extern "C" void __cxa_free_exception(void *thrown_exception) throw();

#pragma GCC visibility push(hidden)
extern "C" void *__cxa_allocate_dependent_exception() throw();
extern "C" void __cxa_free_dependent_exception(void *thrown_exception) throw();
#pragma GCC visibility pop

// Throw the exception.
extern "C" void __cxa_throw (void *thrown_exception,
                             std::type_info *tinfo,
                             void (*dest) (void *))
     __attribute__((noreturn));

// Used to implement exception handlers.
extern "C" void *__cxa_get_exception_ptr (void *) throw();
extern "C" void *__cxa_begin_catch (void *) throw();
extern "C" void __cxa_end_catch ();
extern "C" void __cxa_rethrow () __attribute__((noreturn));

// These facilitate code generation for recurring situations.
extern "C" void __cxa_bad_cast ();
extern "C" void __cxa_bad_typeid ();

// @@@ These are not directly specified by the IA-64 C++ ABI.

// Handles re-checking the exception specification if unexpectedHandler
// throws, and if bad_exception needs to be thrown.  Called from the
// compiler.
extern "C" void __cxa_call_unexpected (void *) __attribute__((noreturn));
extern "C" void __cxa_call_terminate (void*) __attribute__((noreturn));

#ifdef __ARM_EABI_UNWINDER__
// Arm EABI specified routines.
typedef enum {
  ctm_failed = 0,
  ctm_succeeded = 1,
  ctm_succeeded_with_ptr_to_base = 2
} __cxa_type_match_result;
extern "C" bool __cxa_type_match(_Unwind_Exception*, const std::type_info*,
                 bool, void**);
extern "C" void __cxa_begin_cleanup (_Unwind_Exception*);
extern "C" void __cxa_end_cleanup (void);
#endif

// These are explicitly GNU C++ specific.

// Acquire the C++ exception header from the C++ object.
static inline __cxa_exception *
__get_exception_header_from_obj (void *ptr)
{
  return reinterpret_cast<__cxa_exception *>(ptr) - 1;
}

// Acquire the C++ exception header from the generic exception header.
static inline __cxa_exception *
__get_exception_header_from_ue (_Unwind_Exception *exc)
{
  return reinterpret_cast<__cxa_exception *>(exc + 1) - 1;
}

#ifdef __ARM_EABI_UNWINDER__
static inline bool
__is_gxx_exception_class(_Unwind_Exception_Class c)
{
  // TODO: Take advantage of the fact that c will always be word aligned.
  return c[0] == 'G'
     && c[1] == 'N'
     && c[2] == 'U'
     && c[3] == 'C'
     && c[4] == 'C'
     && c[5] == '+'
     && c[6] == '+';
}

static inline void
__GXX_INIT_EXCEPTION_CLASS(_Unwind_Exception_Class c)
{
  c[0] = 'G';
  c[1] = 'N';
  c[2] = 'U';
  c[3] = 'C';
  c[4] = 'C';
  c[5] = '+';
  c[6] = '+';
  c[7] = '\0';
}

static inline void*
__gxx_caught_object(_Unwind_Exception* eo)
{
  return (void*)eo->barrier_cache.bitpattern[0];
}
#else // !__ARM_EABI_UNWINDER__
// This is the exception class we report -- "GNUCC++\0".
const _Unwind_Exception_Class __gxx_exception_class
= ((((((((_Unwind_Exception_Class) 'G' 
     << 8 | (_Unwind_Exception_Class) 'N')
    << 8 | (_Unwind_Exception_Class) 'U')
       << 8 | (_Unwind_Exception_Class) 'C')
      << 8 | (_Unwind_Exception_Class) 'C')
     << 8 | (_Unwind_Exception_Class) '+')
    << 8 | (_Unwind_Exception_Class) '+')
   << 8 | (_Unwind_Exception_Class) '\0');

static inline bool
__is_gxx_exception_class(_Unwind_Exception_Class c)
{
  return (c & ((_Unwind_Exception_Class)~0 << 8)) == __gxx_exception_class;
}

#define __GXX_INIT_EXCEPTION_CLASS(c) c = __gxx_exception_class

// GNU C++ personality routine, Version 0.
extern "C" _Unwind_Reason_Code __gxx_personality_v0
     (int, _Unwind_Action, _Unwind_Exception_Class,
      struct _Unwind_Exception *, struct _Unwind_Context *);

// GNU C++ sjlj personality routine, Version 0.
extern "C" _Unwind_Reason_Code __gxx_personality_sj0
     (int, _Unwind_Action, _Unwind_Exception_Class,
      struct _Unwind_Exception *, struct _Unwind_Context *);

static inline void*
__gxx_caught_object(_Unwind_Exception* eo)
{
  __cxa_exception* header = __get_exception_header_from_ue (eo);
  return header->adjustedPtr;
}
#endif // !__ARM_EABI_UNWINDER__

} /* namespace __cxxabiv1 */

#pragma GCC visibility pop

#endif // _UNWIND_CXX_H