@ -1,16 +1,60 @@
typedef struct objc_object * id ;
# include <atomic>
# include <stdlib.h>
# include <stdio.h>
# include "dwarf_eh.h"
# include "objcxx_eh.h"
# include <atomic>
# include "visibility.h"
# include "objc/runtime.h"
/**
* Helper function that has a custom personality function .
* This calls ` cxx_throw ` and has a destructor that must be run . We intercept
* the personality function calls and inspect the in - flight C + + exception .
*/
int eh_trampoline ( ) ;
uint64_t cxx_exception_class ;
extern " C " void * __cxa_allocate_exception ( size_t ) noexcept ;
/**
* Our own definitions of C + + ABI functions and types . These are provided
* because this file must not include cxxabi . h . We need to handle subtly
* different variations of the ABI and including one specific implementation
* would make that very difficult .
*/
namespace __cxxabiv1
{
/**
* Type info for classes . Forward declared because the GNU ABI provides a
* method on all type_info objects that the dynamic the dynamic cast header
* needs .
*/
struct __class_type_info ;
/**
* The C + + in - flight exception object . We will derive the offset of fields
* in this , so we do not ever actually see a concrete definition of it .
*/
struct __cxa_exception ;
/**
* The public ABI structure for current exception state .
*/
struct __cxa_eh_globals
{
/**
* The current exception that has been caught .
*/
__cxa_exception * caughtExceptions ;
/**
* The number of uncaught exceptions still in flight .
*/
unsigned int uncaughtExceptions ;
} ;
/**
* Retrieve the above structure .
*/
extern " C " __cxa_eh_globals * __cxa_get_globals ( ) ;
}
namespace std
@ -18,13 +62,6 @@ namespace std
struct type_info ;
}
extern " C "
void __cxa_throw ( void * thrown_exception , std : : type_info * tinfo ,
void ( * dest ) ( void * ) ) ;
extern " C "
void * __cxa_current_primary_exception ( ) ;
using namespace __cxxabiv1 ;
// Define some C++ ABI types here, rather than including them. This prevents
@ -69,10 +106,103 @@ namespace std
} ;
}
using namespace std ;
namespace
{
/**
* Helper needed by the unwind helper headers .
*/
inline _Unwind_Reason_Code continueUnwinding ( struct _Unwind_Exception * ex ,
struct _Unwind_Context * context )
{
# if defined(__arm__) && !defined(__ARM_DWARF_EH__)
if ( __gnu_unwind_frame ( ex , context ) ! = _URC_OK ) { return _URC_FAILURE ; }
# endif
return _URC_CONTINUE_UNWIND ;
}
/**
* Flag indicating that we ' ve already inspected a C + + exception and found all
* of the offsets .
*/
std : : atomic < bool > done_setup ;
/**
* The offset of the C + + type_info object in a thrown exception from the unwind
* header in a ` __cxa_exception ` .
*/
std : : atomic < ptrdiff_t > type_info_offset ;
/**
* The offset of the reference count in a
*/
std : : atomic < ptrdiff_t > refcount_offset ;
/**
* The size of the ` _Unwind_Exception ` ( including padding ) in a
* ` __cxa_exception ` .
*/
std : : atomic < size_t > exception_struct_size ;
/**
* Helper function to find a particular value scanning backwards in a
* structure .
*/
template < typename T >
ptrdiff_t find_backwards ( void * addr , T val )
{
T * ptr = reinterpret_cast < T * > ( addr ) ;
for ( ptrdiff_t disp = - 1 ; ( disp * sizeof ( T ) > - 128 ) ; disp - - )
{
if ( ptr [ disp ] = = val )
{
return disp * sizeof ( T ) ;
}
}
fprintf ( stderr , " Unable to find field in C++ exception structure \n " ) ;
abort ( ) ;
}
static std : : atomic < ptrdiff_t > exception_object_offset ;
static std : : atomic < ptrdiff_t > exception_type_offset ;
/**
* Helper function to find a particular value scanning forwards in a
* structure .
*/
template < typename T >
ptrdiff_t find_forwards ( void * addr , T val )
{
T * ptr = reinterpret_cast < T * > ( addr ) ;
for ( ptrdiff_t disp = 0 ; ( disp * sizeof ( T ) < 256 ) ; disp + + )
{
if ( ptr [ disp ] = = val )
{
return disp * sizeof ( T ) ;
}
}
fprintf ( stderr , " Unable to find field in C++ exception structure \n " ) ;
abort ( ) ;
}
template < typename T >
T * pointer_add ( void * ptr , ptrdiff_t offset )
{
return reinterpret_cast < T * > ( reinterpret_cast < char * > ( ptr ) + offset ) ;
}
/**
* Exception cleanup function for C + + exceptions that wrap Objective - C
* exceptions .
*/
void exception_cleanup ( _Unwind_Reason_Code reason ,
struct _Unwind_Exception * ex )
{
// __cxa_exception takes a pointer to the end of the __cxa_exception
// structure, and so we find that by adding the size of the generic
// exception structure + padding to the pointer to the generic exception
// structure field of the enclosing structure.
auto * cxxEx = pointer_add < __cxa_exception > ( ex , exception_struct_size ) ;
__cxa_free_exception ( cxxEx ) ;
}
}
using namespace std ;
static BOOL isKindOfClass ( Class thrown , Class type )
@ -189,58 +319,28 @@ gnustep::libobjc::__objc_id_type_info __objc_id_type_info;
struct _Unwind_Exception * objc_init_cxx_exception ( id obj )
{
void * cxxexception = nullptr ;
try
{
id * exception_object = static_cast < id * > ( __cxa_allocate_exception ( sizeof ( id ) ) ) ;
* exception_object = obj ;
__cxa_throw ( exception_object , & __objc_id_type_info , nullptr ) ;
}
catch ( . . . )
{
cxxexception = __cxa_current_primary_exception ( ) ;
}
assert ( cxxexception ) ;
uint64_t * ehcls = reinterpret_cast < uint64_t * > ( cxxexception ) ;
ehcls - - ;
int count = 1 ;
while ( * ehcls ! = cxx_exception_class )
{
ehcls - - ;
count + + ;
assert ( ( count < 8 ) & & " Exception structure appears to be corrupt " ) ;
}
ptrdiff_t displacement = reinterpret_cast < const char * > ( cxxexception ) - reinterpret_cast < const char * > ( ehcls ) ;
assert ( ( exception_object_offset = = 0 ) | | ( exception_object_offset = = displacement ) ) ;
exception_object_offset = displacement ;
std : : type_info * * ehtype = reinterpret_cast < std : : type_info * * > ( ehcls ) ;
ehtype - - ;
count = 1 ;
while ( * ehtype ! = & __objc_id_type_info )
{
ehtype - - ;
count + + ;
assert ( ( count < 32 ) & & " Exception structure appears to be corrupt " ) ;
}
displacement = reinterpret_cast < const char * > ( ehtype ) - reinterpret_cast < const char * > ( ehcls ) ;
assert ( ( exception_type_offset = = 0 ) | | ( exception_type_offset = = displacement ) ) ;
exception_type_offset = displacement ;
return reinterpret_cast < _Unwind_Exception * > ( ehcls ) ;
id * newEx = static_cast < id * > ( __cxa_allocate_exception ( sizeof ( id ) ) ) ;
* newEx = obj ;
_Unwind_Exception * ex = pointer_add < _Unwind_Exception > ( newEx , - exception_struct_size ) ;
* pointer_add < std : : type_info * > ( ex , type_info_offset ) = & __objc_id_type_info ;
ex - > exception_class = cxx_exception_class ;
ex - > exception_cleanup = exception_cleanup ;
__cxa_get_globals ( ) - > uncaughtExceptions + + ;
return ex ;
}
void * objc_object_for_cxx_exception ( void * thrown_exception , int * isValid )
{
ptrdiff_t type_offset = exception_ type_offset;
ptrdiff_t type_offset = type_info_offset ;
if ( type_offset = = 0 )
{
* isValid = 0 ;
return nullptr ;
}
const std : : type_info * thrownType =
* reinterpret_cast < const std : : type_info * * > ( reinterpret_cast < char * > ( thrown_exception ) + type_offset ) ;
* pointer_add < const std : : type_info * > ( thrown_exception , type_offset ) ;
if ( ! dynamic_cast < const gnustep : : libobjc : : __objc_id_type_info * > ( thrownType ) & &
! dynamic_cast < const gnustep : : libobjc : : __objc_class_type_info * > ( thrownType ) )
{
@ -248,18 +348,113 @@ void* objc_object_for_cxx_exception(void *thrown_exception, int *isValid)
return 0 ;
}
* isValid = 1 ;
return * reinterpret_cast < id * > ( reinterpret_cast < char * > ( thrown_exception ) + exception_object_offset ) ;
return * pointer_add < id > ( thrown_exception , exception_struct_size ) ;
}
/*
void print_type_info ( void * thrown_exception )
} // extern "C"
/**
* C + + structure that is thrown through a frame with the ` test_eh_personality `
* personality function . This contains a well - known value that we can search
* for after the unwind header .
*/
struct
PRIVATE
MagicValueHolder
{
__cxa_exception * ex = ( __cxa_exception * ) ( ( char * ) thrown_exception -
offsetof ( struct __cxa_exception , unwindHeader ) ) ;
fprintf ( stderr , " Type info: %s \n " , ex - > exceptionType - > name ( ) ) ;
fprintf ( stderr , " offset is: %d \n " , offsetof ( struct __cxa_exception , unwindHeader ) ) ;
/**
* The constant that we will search for to identify this object .
*/
static constexpr uint32_t magic = 0x01020304 ;
/**
* The single field in this structure .
*/
uint32_t magic_value ;
/**
* Constructor . Initialises the field with the magic constant .
*/
MagicValueHolder ( ) { magic_value = magic ; }
} ;
/**
* Function that simply throws an instance of ` MagicValueHolder ` .
*/
PRIVATE void cxx_throw ( )
{
MagicValueHolder x ;
throw x ;
}
/**
* Personality function that wraps the C + + personality and inspects the C + +
* exception structure on the way past . This should be used only for the
* ` eh_trampoline ` function .
*/
extern " C "
PRIVATE
BEGIN_PERSONALITY_FUNCTION ( test_eh_personality )
// Don't bother with a mutex here. It doesn't matter if two threads set
// these values at the same time.
if ( ! done_setup )
{
uint64_t cls = __builtin_bswap64 ( exceptionClass ) ;
type_info_offset = find_backwards ( exceptionObject , & typeid ( MagicValueHolder ) ) ;
# ifdef __LP64__
// On 64-bit platforms, the refcount is added to the front of the
// structure.
ptrdiff_t refcount_backwards_offset = type_info_offset - sizeof ( uintptr_t ) ;
# else
// On 32-bit platforms, this should be immediately before the
// _Unwind_Exception in some spare padding, but libsupc++ puts it in
// the same place as for 64-bit. Try the one that's definitely in the
// object first and then fall back to the other...
ptrdiff_t refcount_backwards_offset = - sizeof ( uint32_t ) ;
auto read_offset = [ ] ( void * obj , ptrdiff_t offset )
{
char * addr = reinterpret_cast < char * > ( obj ) + offset ;
uintptr_t v = * reinterpret_cast < uintptr_t * > ( addr ) ;
return v ;
} ;
if ( read_offset ( exceptionObject , refcount_backwards_offset ) ! = 1 )
{
refcount_backwards_offset = type_info_offset - sizeof ( uintptr_t ) ;
}
if ( read_offset ( exceptionObject , refcount_backwards_offset ) ! = 1 )
{
fprintf ( stderr , " Unable to find refcount field \n " ) ;
abort ( ) ;
}
# endif
exception_struct_size = find_forwards ( exceptionObject , MagicValueHolder : : magic ) ;
cxx_exception_class = exceptionClass ;
done_setup = true ;
}
return CALL_PERSONALITY_FUNCTION ( __gxx_personality_v0 ) ;
}
} // extern "C"
/**
* Probe the C + + exception handling implementation . This throws a C + +
* exception through a function that uses ` test_eh_personality ` as its
* personality function , allowing us to inspect a C + + exception that is in a
* known state .
*/
extern " C " void test_cxx_eh_implementation ( )
{
if ( done_setup )
{
return ;
}
bool caught = false ;
try
{
eh_trampoline ( ) ;
}
catch ( MagicValueHolder )
{
caught = true ;
}
assert ( caught ) ;
}
David Chisnall
6 years ago