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Diffstat (limited to 'src/cxa_exception.cpp')
| -rw-r--r-- | src/cxa_exception.cpp | 622 |
1 files changed, 622 insertions, 0 deletions
diff --git a/src/cxa_exception.cpp b/src/cxa_exception.cpp new file mode 100644 index 0000000..744dddd --- /dev/null +++ b/src/cxa_exception.cpp @@ -0,0 +1,622 @@ +//===------------------------- 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://mentorembedded.github.io/cxx-abi/abi-eh.html +// +//===----------------------------------------------------------------------===// + +#include "cxxabi.h" + +#include <exception> // for std::terminate +#include <cstdlib> // for malloc, free +#include <cstring> // for memset +#include <pthread.h> + +#include "cxa_exception.hpp" +#include "cxa_handlers.hpp" + +// +---------------------------+-----------------------------+---------------+ +// | __cxa_exception | _Unwind_Exception CLNGC++\0 | thrown object | +// +---------------------------+-----------------------------+---------------+ +// ^ +// | +// +-------------------------------------------------------+ +// | +// +---------------------------+-----------------------------+ +// | __cxa_dependent_exception | _Unwind_Exception CLNGC++\1 | +// +---------------------------+-----------------------------+ + +namespace __cxxabiv1 { + +#pragma GCC visibility push(default) + +// Utility routines +static +inline +__cxa_exception* +cxa_exception_from_thrown_object(void* thrown_object) +{ + return static_cast<__cxa_exception*>(thrown_object) - 1; +} + +// Note: This is never called when exception_header is masquerading as a +// __cxa_dependent_exception. +static +inline +void* +thrown_object_from_cxa_exception(__cxa_exception* exception_header) +{ + return static_cast<void*>(exception_header + 1); +} + +// Get the exception object from the unwind pointer. +// Relies on the structure layout, where the unwind pointer is right in +// front of the user's exception object +static +inline +__cxa_exception* +cxa_exception_from_exception_unwind_exception(_Unwind_Exception* unwind_exception) +{ + return cxa_exception_from_thrown_object(unwind_exception + 1 ); +} + +static +inline +size_t +cxa_exception_size_from_exception_thrown_size(size_t size) +{ + return size + sizeof (__cxa_exception); +} + +static void setExceptionClass(_Unwind_Exception* unwind_exception) { + unwind_exception->exception_class = kOurExceptionClass; +} + +static void setDependentExceptionClass(_Unwind_Exception* unwind_exception) { + unwind_exception->exception_class = kOurDependentExceptionClass; +} + +// Is it one of ours? +static bool isOurExceptionClass(const _Unwind_Exception* unwind_exception) { + return (unwind_exception->exception_class & get_vendor_and_language) == + (kOurExceptionClass & get_vendor_and_language); +} + +static bool isDependentException(_Unwind_Exception* unwind_exception) { + return (unwind_exception->exception_class & 0xFF) == 0x01; +} + +// This does not need to be atomic +static inline int incrementHandlerCount(__cxa_exception *exception) { + return ++exception->handlerCount; +} + +// This does not need to be atomic +static inline int decrementHandlerCount(__cxa_exception *exception) { + return --exception->handlerCount; +} + +#include "fallback_malloc.ipp" + +// Allocate some memory from _somewhere_ +static void *do_malloc(size_t size) { + void *ptr = std::malloc(size); + if (NULL == ptr) // if malloc fails, fall back to emergency stash + ptr = fallback_malloc(size); + return ptr; +} + +static void do_free(void *ptr) { + is_fallback_ptr(ptr) ? fallback_free(ptr) : std::free(ptr); +} + +/* + If reason isn't _URC_FOREIGN_EXCEPTION_CAUGHT, then the terminateHandler + stored in exc is called. Otherwise the exceptionDestructor stored in + exc is called, and then the memory for the exception is deallocated. + + This is never called for a __cxa_dependent_exception. +*/ +static +void +exception_cleanup_func(_Unwind_Reason_Code reason, _Unwind_Exception* unwind_exception) +{ + __cxa_exception* exception_header = cxa_exception_from_exception_unwind_exception(unwind_exception); + if (_URC_FOREIGN_EXCEPTION_CAUGHT != reason) + std::__terminate(exception_header->terminateHandler); + // Just in case there exists a dependent exception that is pointing to this, + // check the reference count and only destroy this if that count goes to zero. + __cxa_decrement_exception_refcount(unwind_exception + 1); +} + +static LIBCXXABI_NORETURN void failed_throw(__cxa_exception* exception_header) { +// Section 2.5.3 says: +// * For purposes of this ABI, several things are considered exception handlers: +// ** A terminate() call due to a throw. +// and +// * Upon entry, Following initialization of the catch parameter, +// a handler must call: +// * void *__cxa_begin_catch(void *exceptionObject ); + (void) __cxa_begin_catch(&exception_header->unwindHeader); + std::__terminate(exception_header->terminateHandler); +} + +extern "C" { + +// Allocate a __cxa_exception object, and zero-fill it. +// Reserve "thrown_size" bytes on the end for the user's exception +// object. Zero-fill the object. If memory can't be allocated, call +// std::terminate. Return a pointer to the memory to be used for the +// user's exception object. +void * __cxa_allocate_exception (size_t thrown_size) throw() { + size_t actual_size = cxa_exception_size_from_exception_thrown_size(thrown_size); + __cxa_exception* exception_header = static_cast<__cxa_exception*>(do_malloc(actual_size)); + if (NULL == exception_header) + std::terminate(); + std::memset(exception_header, 0, actual_size); + return thrown_object_from_cxa_exception(exception_header); +} + + +// Free a __cxa_exception object allocated with __cxa_allocate_exception. +void __cxa_free_exception (void * thrown_object) throw() { + do_free(cxa_exception_from_thrown_object(thrown_object)); +} + + +// This function shall allocate a __cxa_dependent_exception and +// return a pointer to it. (Really to the object, not past its' end). +// Otherwise, it will work like __cxa_allocate_exception. +void * __cxa_allocate_dependent_exception () { + size_t actual_size = sizeof(__cxa_dependent_exception); + void *ptr = do_malloc(actual_size); + if (NULL == ptr) + std::terminate(); + std::memset(ptr, 0, actual_size); + return ptr; +} + + +// This function shall free a dependent_exception. +// It does not affect the reference count of the primary exception. +void __cxa_free_dependent_exception (void * dependent_exception) { + do_free(dependent_exception); +} + + +// 2.4.3 Throwing the Exception Object +/* +After constructing the exception object with the throw argument value, +the generated code calls the __cxa_throw runtime library routine. This +routine never returns. + +The __cxa_throw routine will do the following: + +* Obtain the __cxa_exception header from the thrown exception object address, +which can be computed as follows: + __cxa_exception *header = ((__cxa_exception *) thrown_exception - 1); +* Save the current unexpected_handler and terminate_handler in the __cxa_exception header. +* Save the tinfo and dest arguments in the __cxa_exception header. +* Set the exception_class field in the unwind header. This is a 64-bit value +representing the ASCII string "XXXXC++\0", where "XXXX" is a +vendor-dependent string. That is, for implementations conforming to this +ABI, the low-order 4 bytes of this 64-bit value will be "C++\0". +* Increment the uncaught_exception flag. +* Call _Unwind_RaiseException in the system unwind library, Its argument is the +pointer to the thrown exception, which __cxa_throw itself received as an argument. +__Unwind_RaiseException begins the process of stack unwinding, described +in Section 2.5. In special cases, such as an inability to find a +handler, _Unwind_RaiseException may return. In that case, __cxa_throw +will call terminate, assuming that there was no handler for the +exception. +*/ +LIBCXXABI_NORETURN +void +__cxa_throw(void* thrown_object, std::type_info* tinfo, void (*dest)(void*)) +{ + __cxa_eh_globals *globals = __cxa_get_globals(); + __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object); + + exception_header->unexpectedHandler = std::get_unexpected(); + exception_header->terminateHandler = std::get_terminate(); + exception_header->exceptionType = tinfo; + exception_header->exceptionDestructor = dest; + setExceptionClass(&exception_header->unwindHeader); + exception_header->referenceCount = 1; // This is a newly allocated exception, no need for thread safety. + globals->uncaughtExceptions += 1; // Not atomically, since globals are thread-local + + exception_header->unwindHeader.exception_cleanup = exception_cleanup_func; +#if __arm__ + _Unwind_SjLj_RaiseException(&exception_header->unwindHeader); +#else + _Unwind_RaiseException(&exception_header->unwindHeader); +#endif + // This only happens when there is no handler, or some unexpected unwinding + // error happens. + failed_throw(exception_header); +} + + +// 2.5.3 Exception Handlers +/* +The adjusted pointer is computed by the personality routine during phase 1 + and saved in the exception header (either __cxa_exception or + __cxa_dependent_exception). + + Requires: exception is native +*/ +void* +__cxa_get_exception_ptr(void* unwind_exception) throw() +{ + return cxa_exception_from_exception_unwind_exception + ( + static_cast<_Unwind_Exception*>(unwind_exception) + )->adjustedPtr; +} + +/* +This routine can catch foreign or native exceptions. If native, the exception +can be a primary or dependent variety. This routine may remain blissfully +ignorant of whether the native exception is primary or dependent. + +If the exception is native: +* Increment's the exception's handler count. +* Push the exception on the stack of currently-caught exceptions if it is not + already there (from a rethrow). +* Decrements the uncaught_exception count. +* Returns the adjusted pointer to the exception object, which is stored in + the __cxa_exception by the personality routine. + +If the exception is foreign, this means it did not originate from one of throw +routines. The foreign exception does not necessarily have a __cxa_exception +header. However we can catch it here with a catch (...), or with a call +to terminate or unexpected during unwinding. +* Do not try to increment the exception's handler count, we don't know where + it is. +* Push the exception on the stack of currently-caught exceptions only if the + stack is empty. The foreign exception has no way to link to the current + top of stack. If the stack is not empty, call terminate. Even with an + empty stack, this is hacked in by pushing a pointer to an imaginary + __cxa_exception block in front of the foreign exception. It would be better + if the __cxa_eh_globals structure had a stack of _Unwind_Exception, but it + doesn't. It has a stack of __cxa_exception (which has a next* in it). +* Do not decrement the uncaught_exception count because we didn't increment it + in __cxa_throw (or one of our rethrow functions). +* If we haven't terminated, assume the exception object is just past the + _Unwind_Exception and return a pointer to that. +*/ +void* +__cxa_begin_catch(void* unwind_arg) throw() +{ + _Unwind_Exception* unwind_exception = static_cast<_Unwind_Exception*>(unwind_arg); + bool native_exception = isOurExceptionClass(unwind_exception); + __cxa_eh_globals* globals = __cxa_get_globals(); + // exception_header is a hackish offset from a foreign exception, but it + // works as long as we're careful not to try to access any __cxa_exception + // parts. + __cxa_exception* exception_header = + cxa_exception_from_exception_unwind_exception + ( + static_cast<_Unwind_Exception*>(unwind_exception) + ); + if (native_exception) + { + // Increment the handler count, removing the flag about being rethrown + exception_header->handlerCount = exception_header->handlerCount < 0 ? + -exception_header->handlerCount + 1 : exception_header->handlerCount + 1; + // place the exception on the top of the stack if it's not already + // there by a previous rethrow + if (exception_header != globals->caughtExceptions) + { + exception_header->nextException = globals->caughtExceptions; + globals->caughtExceptions = exception_header; + } + globals->uncaughtExceptions -= 1; // Not atomically, since globals are thread-local + return exception_header->adjustedPtr; + } + // Else this is a foreign exception + // If the caughtExceptions stack is not empty, terminate + if (globals->caughtExceptions != 0) + std::terminate(); + // Push the foreign exception on to the stack + globals->caughtExceptions = exception_header; + return unwind_exception + 1; +} + + +/* +Upon exit for any reason, a handler must call: + void __cxa_end_catch (); + +This routine can be called for either a native or foreign exception. +For a native exception: +* Locates the most recently caught exception and decrements its handler count. +* Removes the exception from the caught exception stack, if the handler count goes to zero. +* If the handler count goes down to zero, and the exception was not re-thrown + by throw, it locates the primary exception (which may be the same as the one + it's handling) and decrements its reference count. If that reference count + goes to zero, the function destroys the exception. In any case, if the current + exception is a dependent exception, it destroys that. + +For a foreign exception: +* If it has been rethrown, there is nothing to do. +* Otherwise delete the exception and pop the catch stack to empty. +*/ +void __cxa_end_catch() +{ + static_assert(sizeof(__cxa_exception) == sizeof(__cxa_dependent_exception), + "sizeof(__cxa_exception) must be equal to sizeof(__cxa_dependent_exception)"); + __cxa_eh_globals* globals = __cxa_get_globals_fast(); // __cxa_get_globals called in __cxa_begin_catch + __cxa_exception* exception_header = globals->caughtExceptions; + // If we've rethrown a foreign exception, then globals->caughtExceptions + // will have been made an empty stack by __cxa_rethrow() and there is + // nothing more to be done. Do nothing! + if (NULL != exception_header) + { + bool native_exception = isOurExceptionClass(&exception_header->unwindHeader); + if (native_exception) + { + // This is a native exception + if (exception_header->handlerCount < 0) + { + // The exception has been rethrown by __cxa_rethrow, so don't delete it + if (0 == incrementHandlerCount(exception_header)) + { + // Remove from the chain of uncaught exceptions + globals->caughtExceptions = exception_header->nextException; + // but don't destroy + } + // Keep handlerCount negative in case there are nested catch's + // that need to be told that this exception is rethrown. Don't + // erase this rethrow flag until the exception is recaught. + } + else + { + // The native exception has not been rethrown + if (0 == decrementHandlerCount(exception_header)) + { + // Remove from the chain of uncaught exceptions + globals->caughtExceptions = exception_header->nextException; + // Destroy this exception, being careful to distinguish + // between dependent and primary exceptions + if (isDependentException(&exception_header->unwindHeader)) + { + // Reset exception_header to primaryException and deallocate the dependent exception + __cxa_dependent_exception* dep_exception_header = + reinterpret_cast<__cxa_dependent_exception*>(exception_header); + exception_header = + cxa_exception_from_thrown_object(dep_exception_header->primaryException); + __cxa_free_dependent_exception(dep_exception_header); + } + // Destroy the primary exception only if its referenceCount goes to 0 + // (this decrement must be atomic) + __cxa_decrement_exception_refcount(thrown_object_from_cxa_exception(exception_header)); + } + } + } + else + { + // The foreign exception has not been rethrown. Pop the stack + // and delete it. If there are nested catch's and they try + // to touch a foreign exception in any way, that is undefined + // behavior. They likely can't since the only way to catch + // a foreign exception is with catch (...)! + _Unwind_DeleteException(&globals->caughtExceptions->unwindHeader); + globals->caughtExceptions = 0; + } + } +} + +// Note: exception_header may be masquerading as a __cxa_dependent_exception +// and that's ok. exceptionType is there too. +// However watch out for foreign exceptions. Return null for them. +std::type_info * __cxa_current_exception_type() { +// get the current exception + __cxa_eh_globals *globals = __cxa_get_globals_fast(); + if (NULL == globals) + return NULL; // If there have never been any exceptions, there are none now. + __cxa_exception *exception_header = globals->caughtExceptions; + if (NULL == exception_header) + return NULL; // No current exception + if (!isOurExceptionClass(&exception_header->unwindHeader)) + return NULL; + return exception_header->exceptionType; +} + +// 2.5.4 Rethrowing Exceptions +/* This routine can rethrow native or foreign exceptions. +If the exception is native: +* marks the exception object on top of the caughtExceptions stack + (in an implementation-defined way) as being rethrown. +* If the caughtExceptions stack is empty, it calls terminate() + (see [C++FDIS] [except.throw], 15.1.8). +* It then calls _Unwind_RaiseException which should not return + (terminate if it does). + Note: exception_header may be masquerading as a __cxa_dependent_exception + and that's ok. +*/ +LIBCXXABI_NORETURN +void +__cxa_rethrow() +{ + __cxa_eh_globals* globals = __cxa_get_globals(); + __cxa_exception* exception_header = globals->caughtExceptions; + if (NULL == exception_header) + std::terminate(); // throw; called outside of a exception handler + bool native_exception = isOurExceptionClass(&exception_header->unwindHeader); + if (native_exception) + { + // Mark the exception as being rethrown (reverse the effects of __cxa_begin_catch) + exception_header->handlerCount = -exception_header->handlerCount; + globals->uncaughtExceptions += 1; + // __cxa_end_catch will remove this exception from the caughtExceptions stack if necessary + } + else // this is a foreign exception + { + // The only way to communicate to __cxa_end_catch that we've rethrown + // a foreign exception, so don't delete us, is to pop the stack here + // which must be empty afterwards. Then __cxa_end_catch will do + // nothing + globals->caughtExceptions = 0; + } +#if __arm__ + _Unwind_SjLj_RaiseException(&exception_header->unwindHeader); +#else + _Unwind_RaiseException(&exception_header->unwindHeader); +#endif + + // If we get here, some kind of unwinding error has occurred. + // There is some weird code generation bug happening with + // Apple clang version 4.0 (tags/Apple/clang-418.0.2) (based on LLVM 3.1svn) + // If we call failed_throw here. Turns up with -O2 or higher, and -Os. + __cxa_begin_catch(&exception_header->unwindHeader); + if (native_exception) + std::__terminate(exception_header->terminateHandler); + // Foreign exception: can't get exception_header->terminateHandler + std::terminate(); +} + +/* + If thrown_object is not null, atomically increment the referenceCount field + of the __cxa_exception header associated with the thrown object referred to + by thrown_object. + + Requires: If thrown_object is not NULL, it is a native exception. +*/ +void +__cxa_increment_exception_refcount(void* thrown_object) throw() +{ + if (thrown_object != NULL ) + { + __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object); + __sync_add_and_fetch(&exception_header->referenceCount, 1); + } +} + +/* + If thrown_object is not null, atomically decrement the referenceCount field + of the __cxa_exception header associated with the thrown object referred to + by thrown_object. If the referenceCount drops to zero, destroy and + deallocate the exception. + + Requires: If thrown_object is not NULL, it is a native exception. +*/ +void +__cxa_decrement_exception_refcount(void* thrown_object) throw() +{ + if (thrown_object != NULL ) + { + __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object); + if (__sync_sub_and_fetch(&exception_header->referenceCount, size_t(1)) == 0) + { + if (NULL != exception_header->exceptionDestructor) + exception_header->exceptionDestructor(thrown_object); + __cxa_free_exception(thrown_object); + } + } +} + +/* + Returns a pointer to the thrown object (if any) at the top of the + caughtExceptions stack. Atomically increment the exception's referenceCount. + If there is no such thrown object or if the thrown object is foreign, + returns null. + + We can use __cxa_get_globals_fast here to get the globals because if there have + been no exceptions thrown, ever, on this thread, we can return NULL without + the need to allocate the exception-handling globals. +*/ +void* +__cxa_current_primary_exception() throw() +{ +// get the current exception + __cxa_eh_globals* globals = __cxa_get_globals_fast(); + if (NULL == globals) + return NULL; // If there are no globals, there is no exception + __cxa_exception* exception_header = globals->caughtExceptions; + if (NULL == exception_header) + return NULL; // No current exception + if (!isOurExceptionClass(&exception_header->unwindHeader)) + return NULL; // Can't capture a foreign exception (no way to refcount it) + if (isDependentException(&exception_header->unwindHeader)) { + __cxa_dependent_exception* dep_exception_header = + reinterpret_cast<__cxa_dependent_exception*>(exception_header); + exception_header = cxa_exception_from_thrown_object(dep_exception_header->primaryException); + } + void* thrown_object = thrown_object_from_cxa_exception(exception_header); + __cxa_increment_exception_refcount(thrown_object); + return thrown_object; +} + +/* + If reason isn't _URC_FOREIGN_EXCEPTION_CAUGHT, then the terminateHandler + stored in exc is called. Otherwise the referenceCount stored in the + primary exception is decremented, destroying the primary if necessary. + Finally the dependent exception is destroyed. +*/ +static +void +dependent_exception_cleanup(_Unwind_Reason_Code reason, _Unwind_Exception* unwind_exception) +{ + __cxa_dependent_exception* dep_exception_header = + reinterpret_cast<__cxa_dependent_exception*>(unwind_exception + 1) - 1; + if (_URC_FOREIGN_EXCEPTION_CAUGHT != reason) + std::__terminate(dep_exception_header->terminateHandler); + __cxa_decrement_exception_refcount(dep_exception_header->primaryException); + __cxa_free_dependent_exception(dep_exception_header); +} + +/* + If thrown_object is not null, allocate, initialize and throw a dependent + exception. +*/ +void +__cxa_rethrow_primary_exception(void* thrown_object) +{ + if ( thrown_object != NULL ) + { + // thrown_object guaranteed to be native because + // __cxa_current_primary_exception returns NULL for foreign exceptions + __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object); + __cxa_dependent_exception* dep_exception_header = + static_cast<__cxa_dependent_exception*>(__cxa_allocate_dependent_exception()); + dep_exception_header->primaryException = thrown_object; + __cxa_increment_exception_refcount(thrown_object); + dep_exception_header->exceptionType = exception_header->exceptionType; + dep_exception_header->unexpectedHandler = std::get_unexpected(); + dep_exception_header->terminateHandler = std::get_terminate(); + setDependentExceptionClass(&dep_exception_header->unwindHeader); + __cxa_get_globals()->uncaughtExceptions += 1; + dep_exception_header->unwindHeader.exception_cleanup = dependent_exception_cleanup; +#if __arm__ + _Unwind_SjLj_RaiseException(&dep_exception_header->unwindHeader); +#else + _Unwind_RaiseException(&dep_exception_header->unwindHeader); +#endif + // Some sort of unwinding error. Note that terminate is a handler. + __cxa_begin_catch(&dep_exception_header->unwindHeader); + } + // If we return client will call terminate() +} + +bool +__cxa_uncaught_exception() throw() +{ + // This does not report foreign exceptions in flight + __cxa_eh_globals* globals = __cxa_get_globals_fast(); + if (globals == 0) + return false; + return globals->uncaughtExceptions != 0; +} + +} // extern "C" + +#pragma GCC visibility pop + +} // abi |