exception.cc revision 227973
1#include <stdlib.h> 2#include <dlfcn.h> 3#include <stdio.h> 4#include <string.h> 5#include <stdint.h> 6#include <pthread.h> 7#include "typeinfo.h" 8#include "dwarf_eh.h" 9#include "cxxabi.h" 10 11using namespace ABI_NAMESPACE; 12 13/** 14 * Saves the result of the landing pad that we have found. For ARM, this is 15 * stored in the generic unwind structure, while on other platforms it is 16 * stored in the C++ exception. 17 */ 18static void saveLandingPad(struct _Unwind_Context *context, 19 struct _Unwind_Exception *ucb, 20 struct __cxa_exception *ex, 21 int selector, 22 dw_eh_ptr_t landingPad) 23{ 24#ifdef __arm__ 25 // On ARM, we store the saved exception in the generic part of the structure 26 ucb->barrier_cache.sp = _Unwind_GetGR(context, 13); 27 ucb->barrier_cache.bitpattern[1] = (uint32_t)selector; 28 ucb->barrier_cache.bitpattern[3] = (uint32_t)landingPad; 29#endif 30 // Cache the results for the phase 2 unwind, if we found a handler 31 // and this is not a foreign exception. 32 if (ex) 33 { 34 ex->handlerSwitchValue = selector; 35 ex->catchTemp = landingPad; 36 } 37} 38 39/** 40 * Loads the saved landing pad. Returns 1 on success, 0 on failure. 41 */ 42static int loadLandingPad(struct _Unwind_Context *context, 43 struct _Unwind_Exception *ucb, 44 struct __cxa_exception *ex, 45 unsigned long *selector, 46 dw_eh_ptr_t *landingPad) 47{ 48#ifdef __arm__ 49 *selector = ucb->barrier_cache.bitpattern[1]; 50 *landingPad = (dw_eh_ptr_t)ucb->barrier_cache.bitpattern[3]; 51 return 1; 52#else 53 if (ex) 54 { 55 *selector = ex->handlerSwitchValue; 56 *landingPad = (dw_eh_ptr_t)ex->catchTemp; 57 return 0; 58 } 59 return 0; 60#endif 61} 62 63static inline _Unwind_Reason_Code continueUnwinding(struct _Unwind_Exception *ex, 64 struct _Unwind_Context *context) 65{ 66#ifdef __arm__ 67 if (__gnu_unwind_frame(ex, context) != _URC_OK) { return _URC_FAILURE; } 68#endif 69 return _URC_CONTINUE_UNWIND; 70} 71 72 73extern "C" void __cxa_free_exception(void *thrown_exception); 74extern "C" void __cxa_free_dependent_exception(void *thrown_exception); 75extern "C" void* __dynamic_cast(const void *sub, 76 const __class_type_info *src, 77 const __class_type_info *dst, 78 ptrdiff_t src2dst_offset); 79 80/** 81 * The type of a handler that has been found. 82 */ 83typedef enum 84{ 85 /** No handler. */ 86 handler_none, 87 /** 88 * A cleanup - the exception will propagate through this frame, but code 89 * must be run when this happens. 90 */ 91 handler_cleanup, 92 /** 93 * A catch statement. The exception will not propagate past this frame 94 * (without an explicit rethrow). 95 */ 96 handler_catch 97} handler_type; 98 99/** 100 * Per-thread info required by the runtime. We store a single structure 101 * pointer in thread-local storage, because this tends to be a scarce resource 102 * and it's impolite to steal all of it and not leave any for the rest of the 103 * program. 104 * 105 * Instances of this structure are allocated lazily - at most one per thread - 106 * and are destroyed on thread termination. 107 */ 108struct __cxa_thread_info 109{ 110 /** The termination handler for this thread. */ 111 terminate_handler terminateHandler; 112 /** The unexpected exception handler for this thread. */ 113 unexpected_handler unexpectedHandler; 114 /** 115 * The number of emergency buffers held by this thread. This is 0 in 116 * normal operation - the emergency buffers are only used when malloc() 117 * fails to return memory for allocating an exception. Threads are not 118 * permitted to hold more than 4 emergency buffers (as per recommendation 119 * in ABI spec [3.3.1]). 120 */ 121 int emergencyBuffersHeld; 122 /** 123 * The exception currently running in a cleanup. 124 */ 125 _Unwind_Exception *currentCleanup; 126 /** 127 * The public part of this structure, accessible from outside of this 128 * module. 129 */ 130 __cxa_eh_globals globals; 131}; 132/** 133 * Dependent exception. This 134 */ 135struct __cxa_dependent_exception 136{ 137#if __LP64__ 138 void *primaryException; 139#endif 140 std::type_info *exceptionType; 141 void (*exceptionDestructor) (void *); 142 unexpected_handler unexpectedHandler; 143 terminate_handler terminateHandler; 144 __cxa_exception *nextException; 145 int handlerCount; 146#ifdef __arm__ 147 _Unwind_Exception *nextCleanup; 148 int cleanupCount; 149#endif 150 int handlerSwitchValue; 151 const char *actionRecord; 152 const char *languageSpecificData; 153 void *catchTemp; 154 void *adjustedPtr; 155#if !__LP64__ 156 void *primaryException; 157#endif 158 _Unwind_Exception unwindHeader; 159}; 160 161 162namespace std 163{ 164 void unexpected(); 165 class exception 166 { 167 public: 168 virtual ~exception() throw(); 169 virtual const char* what() const throw(); 170 }; 171 172} 173 174extern "C" std::type_info *__cxa_current_exception_type(); 175 176/** 177 * Class of exceptions to distinguish between this and other exception types. 178 * 179 * The first four characters are the vendor ID. Currently, we use GNUC, 180 * because we aim for ABI-compatibility with the GNU implementation, and 181 * various checks may test for equality of the class, which is incorrect. 182 */ 183static const uint64_t exception_class = 184 EXCEPTION_CLASS('G', 'N', 'U', 'C', 'C', '+', '+', '\0'); 185/** 186 * Class used for dependent exceptions. 187 */ 188static const uint64_t dependent_exception_class = 189 EXCEPTION_CLASS('G', 'N', 'U', 'C', 'C', '+', '+', '\x01'); 190/** 191 * The low four bytes of the exception class, indicating that we conform to the 192 * Itanium C++ ABI. This is currently unused, but should be used in the future 193 * if we change our exception class, to allow this library and libsupc++ to be 194 * linked to the same executable and both to interoperate. 195 */ 196static const uint32_t abi_exception_class = 197 GENERIC_EXCEPTION_CLASS('C', '+', '+', '\0'); 198 199static bool isCXXException(uint64_t cls) 200{ 201 return (cls == exception_class) || (cls == dependent_exception_class); 202} 203 204static bool isDependentException(uint64_t cls) 205{ 206 return cls == dependent_exception_class; 207} 208 209static __cxa_exception *exceptionFromPointer(void *ex) 210{ 211 return (__cxa_exception*)((char*)ex - 212 offsetof(struct __cxa_exception, unwindHeader)); 213} 214static __cxa_exception *realExceptionFromException(__cxa_exception *ex) 215{ 216 if (!isDependentException(ex->unwindHeader.exception_class)) { return ex; } 217 return ((__cxa_exception*)(((__cxa_dependent_exception*)ex)->primaryException))-1; 218} 219 220 221namespace std 222{ 223 // Forward declaration of standard library terminate() function used to 224 // abort execution. 225 void terminate(void); 226} 227 228using namespace ABI_NAMESPACE; 229 230 231 232/** The global termination handler. */ 233static terminate_handler terminateHandler = abort; 234/** The global unexpected exception handler. */ 235static unexpected_handler unexpectedHandler = std::terminate; 236 237/** Key used for thread-local data. */ 238static pthread_key_t eh_key; 239 240 241/** 242 * Cleanup function, allowing foreign exception handlers to correctly destroy 243 * this exception if they catch it. 244 */ 245static void exception_cleanup(_Unwind_Reason_Code reason, 246 struct _Unwind_Exception *ex) 247{ 248 __cxa_free_exception((void*)ex); 249} 250static void dependent_exception_cleanup(_Unwind_Reason_Code reason, 251 struct _Unwind_Exception *ex) 252{ 253 254 __cxa_free_dependent_exception((void*)ex); 255} 256 257/** 258 * Recursively walk a list of exceptions and delete them all in post-order. 259 */ 260static void free_exception_list(__cxa_exception *ex) 261{ 262 if (0 != ex->nextException) 263 { 264 free_exception_list(ex->nextException); 265 } 266 // __cxa_free_exception() expects to be passed the thrown object, which 267 // immediately follows the exception, not the exception itself 268 __cxa_free_exception(ex+1); 269} 270 271/** 272 * Cleanup function called when a thread exists to make certain that all of the 273 * per-thread data is deleted. 274 */ 275static void thread_cleanup(void* thread_info) 276{ 277 __cxa_thread_info *info = (__cxa_thread_info*)thread_info; 278 if (info->globals.caughtExceptions) 279 { 280 free_exception_list(info->globals.caughtExceptions); 281 } 282 free(thread_info); 283} 284 285 286/** 287 * Once control used to protect the key creation. 288 */ 289static pthread_once_t once_control = PTHREAD_ONCE_INIT; 290 291/** 292 * Initialise eh_key. 293 */ 294static void init_key(void) 295{ 296 pthread_key_create(&eh_key, thread_cleanup); 297} 298 299/** 300 * Returns the thread info structure, creating it if it is not already created. 301 */ 302static __cxa_thread_info *thread_info() 303{ 304 pthread_once(&once_control, init_key); 305 __cxa_thread_info *info = (__cxa_thread_info*)pthread_getspecific(eh_key); 306 if (0 == info) 307 { 308 info = (__cxa_thread_info*)calloc(1, sizeof(__cxa_thread_info)); 309 pthread_setspecific(eh_key, info); 310 } 311 return info; 312} 313/** 314 * Fast version of thread_info(). May fail if thread_info() is not called on 315 * this thread at least once already. 316 */ 317static __cxa_thread_info *thread_info_fast() 318{ 319 return (__cxa_thread_info*)pthread_getspecific(eh_key); 320} 321/** 322 * ABI function returning the __cxa_eh_globals structure. 323 */ 324extern "C" __cxa_eh_globals *ABI_NAMESPACE::__cxa_get_globals(void) 325{ 326 return &(thread_info()->globals); 327} 328/** 329 * Version of __cxa_get_globals() assuming that __cxa_get_globals() has already 330 * been called at least once by this thread. 331 */ 332extern "C" __cxa_eh_globals *ABI_NAMESPACE::__cxa_get_globals_fast(void) 333{ 334 return &(thread_info_fast()->globals); 335} 336 337/** 338 * An emergency allocation reserved for when malloc fails. This is treated as 339 * 16 buffers of 1KB each. 340 */ 341static char emergency_buffer[16384]; 342/** 343 * Flag indicating whether each buffer is allocated. 344 */ 345static bool buffer_allocated[16]; 346/** 347 * Lock used to protect emergency allocation. 348 */ 349static pthread_mutex_t emergency_malloc_lock = PTHREAD_MUTEX_INITIALIZER; 350/** 351 * Condition variable used to wait when two threads are both trying to use the 352 * emergency malloc() buffer at once. 353 */ 354static pthread_cond_t emergency_malloc_wait = PTHREAD_COND_INITIALIZER; 355 356/** 357 * Allocates size bytes from the emergency allocation mechanism, if possible. 358 * This function will fail if size is over 1KB or if this thread already has 4 359 * emergency buffers. If all emergency buffers are allocated, it will sleep 360 * until one becomes available. 361 */ 362static char *emergency_malloc(size_t size) 363{ 364 if (size > 1024) { return 0; } 365 366 __cxa_thread_info *info = thread_info(); 367 // Only 4 emergency buffers allowed per thread! 368 if (info->emergencyBuffersHeld > 3) { return 0; } 369 370 pthread_mutex_lock(&emergency_malloc_lock); 371 int buffer = -1; 372 while (buffer < 0) 373 { 374 // While we were sleeping on the lock, another thread might have free'd 375 // enough memory for us to use, so try the allocation again - no point 376 // using the emergency buffer if there is some real memory that we can 377 // use... 378 void *m = calloc(1, size); 379 if (0 != m) 380 { 381 pthread_mutex_unlock(&emergency_malloc_lock); 382 return (char*)m; 383 } 384 for (int i=0 ; i<16 ; i++) 385 { 386 if (!buffer_allocated[i]) 387 { 388 buffer = i; 389 buffer_allocated[i] = true; 390 break; 391 } 392 } 393 // If there still isn't a buffer available, then sleep on the condition 394 // variable. This will be signalled when another thread releases one 395 // of the emergency buffers. 396 if (buffer < 0) 397 { 398 pthread_cond_wait(&emergency_malloc_wait, &emergency_malloc_lock); 399 } 400 } 401 pthread_mutex_unlock(&emergency_malloc_lock); 402 info->emergencyBuffersHeld++; 403 return emergency_buffer + (1024 * buffer); 404} 405 406/** 407 * Frees a buffer returned by emergency_malloc(). 408 * 409 * Note: Neither this nor emergency_malloc() is particularly efficient. This 410 * should not matter, because neither will be called in normal operation - they 411 * are only used when the program runs out of memory, which should not happen 412 * often. 413 */ 414static void emergency_malloc_free(char *ptr) 415{ 416 int buffer = -1; 417 // Find the buffer corresponding to this pointer. 418 for (int i=0 ; i<16 ; i++) 419 { 420 if (ptr == (void*)(emergency_buffer + (1024 * i))) 421 { 422 buffer = i; 423 break; 424 } 425 } 426 assert(buffer > 0 && 427 "Trying to free something that is not an emergency buffer!"); 428 // emergency_malloc() is expected to return 0-initialized data. We don't 429 // zero the buffer when allocating it, because the static buffers will 430 // begin life containing 0 values. 431 memset((void*)ptr, 0, 1024); 432 // Signal the condition variable to wake up any threads that are blocking 433 // waiting for some space in the emergency buffer 434 pthread_mutex_lock(&emergency_malloc_lock); 435 // In theory, we don't need to do this with the lock held. In practice, 436 // our array of bools will probably be updated using 32-bit or 64-bit 437 // memory operations, so this update may clobber adjacent values. 438 buffer_allocated[buffer] = false; 439 pthread_cond_signal(&emergency_malloc_wait); 440 pthread_mutex_unlock(&emergency_malloc_lock); 441} 442 443static char *alloc_or_die(size_t size) 444{ 445 char *buffer = (char*)calloc(1, size); 446 447 // If calloc() doesn't want to give us any memory, try using an emergency 448 // buffer. 449 if (0 == buffer) 450 { 451 buffer = emergency_malloc(size); 452 // This is only reached if the allocation is greater than 1KB, and 453 // anyone throwing objects that big really should know better. 454 if (0 == buffer) 455 { 456 fprintf(stderr, "Out of memory attempting to allocate exception\n"); 457 std::terminate(); 458 } 459 } 460 return buffer; 461} 462static void free_exception(char *e) 463{ 464 // If this allocation is within the address range of the emergency buffer, 465 // don't call free() because it was not allocated with malloc() 466 if ((e > emergency_buffer) && 467 (e < (emergency_buffer + sizeof(emergency_buffer)))) 468 { 469 emergency_malloc_free(e); 470 } 471 else 472 { 473 free(e); 474 } 475} 476 477/** 478 * Allocates an exception structure. Returns a pointer to the space that can 479 * be used to store an object of thrown_size bytes. This function will use an 480 * emergency buffer if malloc() fails, and may block if there are no such 481 * buffers available. 482 */ 483extern "C" void *__cxa_allocate_exception(size_t thrown_size) 484{ 485 size_t size = thrown_size + sizeof(__cxa_exception); 486 char *buffer = alloc_or_die(size); 487 return buffer+sizeof(__cxa_exception); 488} 489 490extern "C" void *__cxa_allocate_dependent_exception(void) 491{ 492 size_t size = sizeof(__cxa_dependent_exception); 493 char *buffer = alloc_or_die(size); 494 return buffer+sizeof(__cxa_dependent_exception); 495} 496 497/** 498 * __cxa_free_exception() is called when an exception was thrown in between 499 * calling __cxa_allocate_exception() and actually throwing the exception. 500 * This happens when the object's copy constructor throws an exception. 501 * 502 * In this implementation, it is also called by __cxa_end_catch() and during 503 * thread cleanup. 504 */ 505extern "C" void __cxa_free_exception(void *thrown_exception) 506{ 507 __cxa_exception *ex = ((__cxa_exception*)thrown_exception) - 1; 508 // Free the object that was thrown, calling its destructor 509 if (0 != ex->exceptionDestructor) 510 { 511 try 512 { 513 ex->exceptionDestructor(thrown_exception); 514 } 515 catch(...) 516 { 517 // FIXME: Check that this is really what the spec says to do. 518 std::terminate(); 519 } 520 } 521 522 free_exception((char*)ex); 523} 524 525static void releaseException(__cxa_exception *exception) 526{ 527 if (isDependentException(exception->unwindHeader.exception_class)) 528 { 529 __cxa_free_dependent_exception(exception+1); 530 return; 531 } 532 if (__sync_sub_and_fetch(&exception->referenceCount, 1) == 0) 533 { 534 // __cxa_free_exception() expects to be passed the thrown object, 535 // which immediately follows the exception, not the exception 536 // itself 537 __cxa_free_exception(exception+1); 538 } 539} 540 541void __cxa_free_dependent_exception(void *thrown_exception) 542{ 543 __cxa_dependent_exception *ex = ((__cxa_dependent_exception*)thrown_exception) - 1; 544 assert(isDependentException(ex->unwindHeader.exception_class)); 545 if (ex->primaryException) 546 { 547 releaseException(realExceptionFromException((__cxa_exception*)ex)); 548 } 549 free_exception((char*)ex); 550} 551 552/** 553 * Callback function used with _Unwind_Backtrace(). 554 * 555 * Prints a stack trace. Used only for debugging help. 556 * 557 * Note: As of FreeBSD 8.1, dladd() still doesn't work properly, so this only 558 * correctly prints function names from public, relocatable, symbols. 559 */ 560static _Unwind_Reason_Code trace(struct _Unwind_Context *context, void *c) 561{ 562 Dl_info myinfo; 563 int mylookup = 564 dladdr((void*)(uintptr_t)__cxa_current_exception_type, &myinfo); 565 void *ip = (void*)_Unwind_GetIP(context); 566 Dl_info info; 567 if (dladdr(ip, &info) != 0) 568 { 569 if (mylookup == 0 || strcmp(info.dli_fname, myinfo.dli_fname) != 0) 570 { 571 printf("%p:%s() in %s\n", ip, info.dli_sname, info.dli_fname); 572 } 573 } 574 return _URC_CONTINUE_UNWIND; 575} 576 577/** 578 * Report a failure that occurred when attempting to throw an exception. 579 * 580 * If the failure happened by falling off the end of the stack without finding 581 * a handler, prints a back trace before aborting. 582 */ 583static void report_failure(_Unwind_Reason_Code err, __cxa_exception *thrown_exception) 584{ 585 switch (err) 586 { 587 default: break; 588 case _URC_FATAL_PHASE1_ERROR: 589 fprintf(stderr, "Fatal error during phase 1 unwinding\n"); 590 break; 591#ifndef __arm__ 592 case _URC_FATAL_PHASE2_ERROR: 593 fprintf(stderr, "Fatal error during phase 2 unwinding\n"); 594 break; 595#endif 596 case _URC_END_OF_STACK: 597 fprintf(stderr, "Terminating due to uncaught exception %p", 598 (void*)thrown_exception); 599 thrown_exception = realExceptionFromException(thrown_exception); 600 static const __class_type_info *e_ti = 601 static_cast<const __class_type_info*>(&typeid(std::exception)); 602 const __class_type_info *throw_ti = 603 dynamic_cast<const __class_type_info*>(thrown_exception->exceptionType); 604 if (throw_ti) 605 { 606 std::exception *e = 607 (std::exception*)e_ti->cast_to((void*)(thrown_exception+1), 608 throw_ti); 609 if (e) 610 { 611 fprintf(stderr, " '%s'", e->what()); 612 } 613 } 614 615 size_t bufferSize = 128; 616 char *demangled = (char*)malloc(bufferSize); 617 const char *mangled = thrown_exception->exceptionType->name(); 618 int status; 619 demangled = __cxa_demangle(mangled, demangled, &bufferSize, &status); 620 fprintf(stderr, " of type %s\n", 621 status == 0 ? (const char*)demangled : mangled); 622 if (status == 0) { free(demangled); } 623 // Print a back trace if no handler is found. 624 // TODO: Make this optional 625 _Unwind_Backtrace(trace, 0); 626 break; 627 } 628 std::terminate(); 629} 630 631static void throw_exception(__cxa_exception *ex) 632{ 633 __cxa_thread_info *info = thread_info(); 634 ex->unexpectedHandler = info->unexpectedHandler; 635 if (0 == ex->unexpectedHandler) 636 { 637 ex->unexpectedHandler = unexpectedHandler; 638 } 639 ex->terminateHandler = info->terminateHandler; 640 if (0 == ex->terminateHandler) 641 { 642 ex->terminateHandler = terminateHandler; 643 } 644 info->globals.uncaughtExceptions++; 645 646 _Unwind_Reason_Code err = _Unwind_RaiseException(&ex->unwindHeader); 647 // The _Unwind_RaiseException() function should not return, it should 648 // unwind the stack past this function. If it does return, then something 649 // has gone wrong. 650 report_failure(err, ex); 651} 652 653 654/** 655 * ABI function for throwing an exception. Takes the object to be thrown (the 656 * pointer returned by __cxa_allocate_exception()), the type info for the 657 * pointee, and the destructor (if there is one) as arguments. 658 */ 659extern "C" void __cxa_throw(void *thrown_exception, 660 std::type_info *tinfo, 661 void(*dest)(void*)) 662{ 663 __cxa_exception *ex = ((__cxa_exception*)thrown_exception) - 1; 664 665 ex->referenceCount = 1; 666 ex->exceptionType = tinfo; 667 668 ex->exceptionDestructor = dest; 669 670 ex->unwindHeader.exception_class = exception_class; 671 ex->unwindHeader.exception_cleanup = exception_cleanup; 672 673 throw_exception(ex); 674} 675 676extern "C" void __cxa_rethrow_primary_exception(void* thrown_exception) 677{ 678 if (NULL == thrown_exception) { return; } 679 680 __cxa_exception *original = exceptionFromPointer(thrown_exception); 681 __cxa_dependent_exception *ex = ((__cxa_dependent_exception*)__cxa_allocate_dependent_exception())-1; 682 683 ex->primaryException = thrown_exception; 684 __cxa_increment_exception_refcount(thrown_exception); 685 686 ex->exceptionType = original->exceptionType; 687 ex->unwindHeader.exception_class = dependent_exception_class; 688 ex->unwindHeader.exception_cleanup = dependent_exception_cleanup; 689 690 throw_exception((__cxa_exception*)ex); 691} 692 693extern "C" void *__cxa_current_primary_exception(void) 694{ 695 __cxa_eh_globals* globals = __cxa_get_globals(); 696 __cxa_exception *ex = globals->caughtExceptions; 697 698 if (0 == ex) { return NULL; } 699 ex = realExceptionFromException(ex); 700 __sync_fetch_and_add(&ex->referenceCount, 1); 701 return ex + 1; 702} 703 704extern "C" void __cxa_increment_exception_refcount(void* thrown_exception) 705{ 706 if (NULL == thrown_exception) { return; } 707 __cxa_exception *ex = ((__cxa_exception*)thrown_exception) - 1; 708 if (isDependentException(ex->unwindHeader.exception_class)) { return; } 709 __sync_fetch_and_add(&ex->referenceCount, 1); 710} 711extern "C" void __cxa_decrement_exception_refcount(void* thrown_exception) 712{ 713 if (NULL == thrown_exception) { return; } 714 __cxa_exception *ex = ((__cxa_exception*)thrown_exception) - 1; 715 releaseException(ex); 716} 717 718/** 719 * ABI function. Rethrows the current exception. Does not remove the 720 * exception from the stack or decrement its handler count - the compiler is 721 * expected to set the landing pad for this function to the end of the catch 722 * block, and then call _Unwind_Resume() to continue unwinding once 723 * __cxa_end_catch() has been called and any cleanup code has been run. 724 */ 725extern "C" void __cxa_rethrow() 726{ 727 __cxa_eh_globals *globals = __cxa_get_globals(); 728 // Note: We don't remove this from the caught list here, because 729 // __cxa_end_catch will be called when we unwind out of the try block. We 730 // could probably make this faster by providing an alternative rethrow 731 // function and ensuring that all cleanup code is run before calling it, so 732 // we can skip the top stack frame when unwinding. 733 __cxa_exception *ex = globals->caughtExceptions; 734 735 if (0 == ex) 736 { 737 fprintf(stderr, 738 "Attempting to rethrow an exception that doesn't exist!\n"); 739 std::terminate(); 740 } 741 742 assert(ex->handlerCount > 0 && "Rethrowing uncaught exception!"); 743 744 // ex->handlerCount will be decremented in __cxa_end_catch in enclosing 745 // catch block 746 747 // Make handler count negative. This will tell __cxa_end_catch that 748 // exception was rethrown and exception object should not be destroyed 749 // when handler count become zero 750 ex->handlerCount = -ex->handlerCount; 751 752 // Continue unwinding the stack with this exception. This should unwind to 753 // the place in the caller where __cxa_end_catch() is called. The caller 754 // will then run cleanup code and bounce the exception back with 755 // _Unwind_Resume(). 756 _Unwind_Reason_Code err = _Unwind_Resume_or_Rethrow(&ex->unwindHeader); 757 report_failure(err, ex); 758} 759 760/** 761 * Returns the type_info object corresponding to the filter. 762 */ 763static std::type_info *get_type_info_entry(_Unwind_Context *context, 764 dwarf_eh_lsda *lsda, 765 int filter) 766{ 767 // Get the address of the record in the table. 768 dw_eh_ptr_t record = lsda->type_table - 769 dwarf_size_of_fixed_size_field(lsda->type_table_encoding)*filter; 770 //record -= 4; 771 dw_eh_ptr_t start = record; 772 // Read the value, but it's probably an indirect reference... 773 int64_t offset = read_value(lsda->type_table_encoding, &record); 774 775 // (If the entry is 0, don't try to dereference it. That would be bad.) 776 if (offset == 0) { return 0; } 777 778 // ...so we need to resolve it 779 return (std::type_info*)resolve_indirect_value(context, 780 lsda->type_table_encoding, offset, start); 781} 782 783 784 785/** 786 * Checks the type signature found in a handler against the type of the thrown 787 * object. If ex is 0 then it is assumed to be a foreign exception and only 788 * matches cleanups. 789 */ 790static bool check_type_signature(__cxa_exception *ex, 791 const std::type_info *type, 792 void *&adjustedPtr) 793{ 794 // TODO: For compatibility with the GNU implementation, we should move this 795 // out into a __do_catch() virtual function in std::type_info 796 void *exception_ptr = (void*)(ex+1); 797 const std::type_info *ex_type = ex->exceptionType; 798 799 const __pointer_type_info *ptr_type = 800 dynamic_cast<const __pointer_type_info*>(ex_type); 801 if (0 != ptr_type) 802 { 803 exception_ptr = *(void**)exception_ptr; 804 } 805 // Always match a catchall, even with a foreign exception 806 // 807 // Note: A 0 here is a catchall, not a cleanup, so we return true to 808 // indicate that we found a catch. 809 // 810 // TODO: Provide a class for matching against foreign exceptions. This is 811 // already done in libobjc2, allowing C++ exceptions to be boxed as 812 // Objective-C objects. We should do something similar, allowing foreign 813 // exceptions to be wrapped in a C++ exception and delivered. 814 if (0 == type) 815 { 816 if (ex) 817 { 818 adjustedPtr = exception_ptr; 819 } 820 return true; 821 } 822 823 if (0 == ex) { return false; } 824 825 const __pointer_type_info *target_ptr_type = 826 dynamic_cast<const __pointer_type_info*>(type); 827 828 if (0 != ptr_type && 0 != target_ptr_type) 829 { 830 if (ptr_type->__flags & ~target_ptr_type->__flags) 831 { 832 // Handler pointer is less qualified 833 return false; 834 } 835 836 // Special case for void* handler. 837 if(*target_ptr_type->__pointee == typeid(void)) 838 { 839 adjustedPtr = exception_ptr; 840 return true; 841 } 842 843 ex_type = ptr_type->__pointee; 844 type = target_ptr_type->__pointee; 845 } 846 847 // If the types are the same, no casting is needed. 848 if (*type == *ex_type) 849 { 850 adjustedPtr = exception_ptr; 851 return true; 852 } 853 854 const __class_type_info *cls_type = 855 dynamic_cast<const __class_type_info*>(ex_type); 856 const __class_type_info *target_cls_type = 857 dynamic_cast<const __class_type_info*>(type); 858 859 if (0 != cls_type && 860 0 != target_cls_type && 861 cls_type->can_cast_to(target_cls_type)) 862 { 863 adjustedPtr = cls_type->cast_to(exception_ptr, target_cls_type); 864 return true; 865 } 866 return false; 867} 868/** 869 * Checks whether the exception matches the type specifiers in this action 870 * record. If the exception only matches cleanups, then this returns false. 871 * If it matches a catch (including a catchall) then it returns true. 872 * 873 * The selector argument is used to return the selector that is passed in the 874 * second exception register when installing the context. 875 */ 876static handler_type check_action_record(_Unwind_Context *context, 877 dwarf_eh_lsda *lsda, 878 dw_eh_ptr_t action_record, 879 __cxa_exception *ex, 880 unsigned long *selector, 881 void *&adjustedPtr) 882{ 883 if (!action_record) { return handler_cleanup; } 884 handler_type found = handler_none; 885 while (action_record) 886 { 887 int filter = read_sleb128(&action_record); 888 dw_eh_ptr_t action_record_offset_base = action_record; 889 int displacement = read_sleb128(&action_record); 890 action_record = displacement ? 891 action_record_offset_base + displacement : 0; 892 // We only check handler types for C++ exceptions - foreign exceptions 893 // are only allowed for cleanup. 894 if (filter > 0 && 0 != ex) 895 { 896 std::type_info *handler_type = get_type_info_entry(context, lsda, filter); 897 if (check_type_signature(ex, handler_type, adjustedPtr)) 898 { 899 *selector = filter; 900 return handler_catch; 901 } 902 } 903 else if (filter < 0 && 0 != ex) 904 { 905 bool matched = false; 906 *selector = filter; 907#ifdef __arm__ 908 filter++; 909 std::type_info *handler_type = get_type_info_entry(context, lsda, filter--); 910 while (handler_type) 911 { 912 if (check_type_signature(ex, handler_type, adjustedPtr)) 913 { 914 matched = true; 915 break; 916 } 917 handler_type = get_type_info_entry(context, lsda, filter--); 918 } 919#else 920 unsigned char *type_index = ((unsigned char*)lsda->type_table - filter - 1); 921 while (*type_index) 922 { 923 std::type_info *handler_type = get_type_info_entry(context, lsda, *(type_index++)); 924 // If the exception spec matches a permitted throw type for 925 // this function, don't report a handler - we are allowed to 926 // propagate this exception out. 927 if (check_type_signature(ex, handler_type, adjustedPtr)) 928 { 929 matched = true; 930 break; 931 } 932 } 933#endif 934 if (matched) { continue; } 935 // If we don't find an allowed exception spec, we need to install 936 // the context for this action. The landing pad will then call the 937 // unexpected exception function. Treat this as a catch 938 return handler_catch; 939 } 940 else if (filter == 0) 941 { 942 *selector = filter; 943 found = handler_cleanup; 944 } 945 } 946 return found; 947} 948 949static void pushCleanupException(_Unwind_Exception *exceptionObject, 950 __cxa_exception *ex) 951{ 952#ifdef __arm__ 953 __cxa_thread_info *info = thread_info_fast(); 954 if (ex) 955 { 956 ex->cleanupCount++; 957 if (ex->cleanupCount > 1) 958 { 959 assert(exceptionObject == info->currentCleanup); 960 return; 961 } 962 ex->nextCleanup = info->currentCleanup; 963 } 964 info->currentCleanup = exceptionObject; 965#endif 966} 967 968/** 969 * The exception personality function. This is referenced in the unwinding 970 * DWARF metadata and is called by the unwind library for each C++ stack frame 971 * containing catch or cleanup code. 972 */ 973extern "C" 974BEGIN_PERSONALITY_FUNCTION(__gxx_personality_v0) 975 // This personality function is for version 1 of the ABI. If you use it 976 // with a future version of the ABI, it won't know what to do, so it 977 // reports a fatal error and give up before it breaks anything. 978 if (1 != version) 979 { 980 return _URC_FATAL_PHASE1_ERROR; 981 } 982 __cxa_exception *ex = 0; 983 __cxa_exception *realEx = 0; 984 985 // If this exception is throw by something else then we can't make any 986 // assumptions about its layout beyond the fields declared in 987 // _Unwind_Exception. 988 bool foreignException = !isCXXException(exceptionClass); 989 990 // If this isn't a foreign exception, then we have a C++ exception structure 991 if (!foreignException) 992 { 993 ex = exceptionFromPointer(exceptionObject); 994 realEx = realExceptionFromException(ex); 995 } 996 997 unsigned char *lsda_addr = 998 (unsigned char*)_Unwind_GetLanguageSpecificData(context); 999 1000 // No LSDA implies no landing pads - try the next frame 1001 if (0 == lsda_addr) { return continueUnwinding(exceptionObject, context); } 1002 1003 // These two variables define how the exception will be handled. 1004 dwarf_eh_action action = {0}; 1005 unsigned long selector = 0; 1006 1007 // During the search phase, we do a complete lookup. If we return 1008 // _URC_HANDLER_FOUND, then the phase 2 unwind will call this function with 1009 // a _UA_HANDLER_FRAME action, telling us to install the handler frame. If 1010 // we return _URC_CONTINUE_UNWIND, we may be called again later with a 1011 // _UA_CLEANUP_PHASE action for this frame. 1012 // 1013 // The point of the two-stage unwind allows us to entirely avoid any stack 1014 // unwinding if there is no handler. If there are just cleanups found, 1015 // then we can just panic call an abort function. 1016 // 1017 // Matching a handler is much more expensive than matching a cleanup, 1018 // because we don't need to bother doing type comparisons (or looking at 1019 // the type table at all) for a cleanup. This means that there is no need 1020 // to cache the result of finding a cleanup, because it's (quite) quick to 1021 // look it up again from the action table. 1022 if (actions & _UA_SEARCH_PHASE) 1023 { 1024 struct dwarf_eh_lsda lsda = parse_lsda(context, lsda_addr); 1025 1026 if (!dwarf_eh_find_callsite(context, &lsda, &action)) 1027 { 1028 // EH range not found. This happens if exception is thrown and not 1029 // caught inside a cleanup (destructor). We should call 1030 // terminate() in this case. The catchTemp (landing pad) field of 1031 // exception object will contain null when personality function is 1032 // called with _UA_HANDLER_FRAME action for phase 2 unwinding. 1033 return _URC_HANDLER_FOUND; 1034 } 1035 1036 handler_type found_handler = check_action_record(context, &lsda, 1037 action.action_record, realEx, &selector, ex->adjustedPtr); 1038 // If there's no action record, we've only found a cleanup, so keep 1039 // searching for something real 1040 if (found_handler == handler_catch) 1041 { 1042 // Cache the results for the phase 2 unwind, if we found a handler 1043 // and this is not a foreign exception. 1044 if (ex) 1045 { 1046 saveLandingPad(context, exceptionObject, ex, selector, action.landing_pad); 1047 ex->languageSpecificData = (const char*)lsda_addr; 1048 ex->actionRecord = (const char*)action.action_record; 1049 // ex->adjustedPtr is set when finding the action record. 1050 } 1051 return _URC_HANDLER_FOUND; 1052 } 1053 return continueUnwinding(exceptionObject, context); 1054 } 1055 1056 1057 // If this is a foreign exception, we didn't have anywhere to cache the 1058 // lookup stuff, so we need to do it again. If this is either a forced 1059 // unwind, a foreign exception, or a cleanup, then we just install the 1060 // context for a cleanup. 1061 if (!(actions & _UA_HANDLER_FRAME)) 1062 { 1063 // cleanup 1064 struct dwarf_eh_lsda lsda = parse_lsda(context, lsda_addr); 1065 dwarf_eh_find_callsite(context, &lsda, &action); 1066 if (0 == action.landing_pad) { return continueUnwinding(exceptionObject, context); } 1067 handler_type found_handler = check_action_record(context, &lsda, 1068 action.action_record, realEx, &selector, ex->adjustedPtr); 1069 // Ignore handlers this time. 1070 if (found_handler != handler_cleanup) { return continueUnwinding(exceptionObject, context); } 1071 pushCleanupException(exceptionObject, ex); 1072 } 1073 else if (foreignException) 1074 { 1075 struct dwarf_eh_lsda lsda = parse_lsda(context, lsda_addr); 1076 dwarf_eh_find_callsite(context, &lsda, &action); 1077 check_action_record(context, &lsda, action.action_record, realEx, 1078 &selector, ex->adjustedPtr); 1079 } 1080 else if (ex->catchTemp == 0) 1081 { 1082 // Uncaught exception in cleanup, calling terminate 1083 std::terminate(); 1084 } 1085 else 1086 { 1087 // Restore the saved info if we saved some last time. 1088 loadLandingPad(context, exceptionObject, ex, &selector, &action.landing_pad); 1089 ex->catchTemp = 0; 1090 ex->handlerSwitchValue = 0; 1091 } 1092 1093 1094 _Unwind_SetIP(context, (unsigned long)action.landing_pad); 1095 _Unwind_SetGR(context, __builtin_eh_return_data_regno(0), 1096 (unsigned long)exceptionObject); 1097 _Unwind_SetGR(context, __builtin_eh_return_data_regno(1), selector); 1098 1099 return _URC_INSTALL_CONTEXT; 1100} 1101 1102/** 1103 * ABI function called when entering a catch statement. The argument is the 1104 * pointer passed out of the personality function. This is always the start of 1105 * the _Unwind_Exception object. The return value for this function is the 1106 * pointer to the caught exception, which is either the adjusted pointer (for 1107 * C++ exceptions) of the unadjusted pointer (for foreign exceptions). 1108 */ 1109#if __GNUC__ > 3 && __GNUC_MINOR__ > 2 1110extern "C" void *__cxa_begin_catch(void *e) throw() 1111#else 1112extern "C" void *__cxa_begin_catch(void *e) 1113#endif 1114{ 1115 // Decrement the uncaught exceptions count 1116 __cxa_eh_globals *globals = __cxa_get_globals(); 1117 globals->uncaughtExceptions--; 1118 _Unwind_Exception *exceptionObject = (_Unwind_Exception*)e; 1119 1120 if (isCXXException(exceptionObject->exception_class)) 1121 { 1122 __cxa_exception *ex = exceptionFromPointer(exceptionObject); 1123 1124 if (ex->handlerCount == 0) 1125 { 1126 // Add this to the front of the list of exceptions being handled 1127 // and increment its handler count so that it won't be deleted 1128 // prematurely. 1129 ex->nextException = globals->caughtExceptions; 1130 globals->caughtExceptions = ex; 1131 } 1132 1133 if (ex->handlerCount < 0) 1134 { 1135 // Rethrown exception is catched before end of catch block. 1136 // Clear the rethrow flag (make value positive) - we are allowed 1137 // to delete this exception at the end of the catch block, as long 1138 // as it isn't thrown again later. 1139 1140 // Code pattern: 1141 // 1142 // try { 1143 // throw x; 1144 // } 1145 // catch() { 1146 // try { 1147 // throw; 1148 // } 1149 // catch() { 1150 // __cxa_begin_catch() <- we are here 1151 // } 1152 // } 1153 ex->handlerCount = -ex->handlerCount + 1; 1154 } 1155 else 1156 { 1157 ex->handlerCount++; 1158 } 1159 1160 return ex->adjustedPtr; 1161 } 1162 // exceptionObject is the pointer to the _Unwind_Exception within the 1163 // __cxa_exception. The throw object is after this 1164 return ((char*)exceptionObject + sizeof(_Unwind_Exception)); 1165} 1166 1167 1168 1169/** 1170 * ABI function called when exiting a catch block. This will free the current 1171 * exception if it is no longer referenced in other catch blocks. 1172 */ 1173extern "C" void __cxa_end_catch() 1174{ 1175 // We can call the fast version here because the slow version is called in 1176 // __cxa_throw(), which must have been called before we end a catch block 1177 __cxa_eh_globals *globals = __cxa_get_globals_fast(); 1178 __cxa_exception *ex = globals->caughtExceptions; 1179 1180 assert(0 != ex && "Ending catch when no exception is on the stack!"); 1181 1182 bool deleteException = true; 1183 1184 if (ex->handlerCount < 0) 1185 { 1186 // exception was rethrown. Exception should not be deleted even if 1187 // handlerCount become zero. 1188 // Code pattern: 1189 // try { 1190 // throw x; 1191 // } 1192 // catch() { 1193 // { 1194 // throw; 1195 // } 1196 // cleanup { 1197 // __cxa_end_catch(); <- we are here 1198 // } 1199 // } 1200 // 1201 1202 ex->handlerCount++; 1203 deleteException = false; 1204 } 1205 else 1206 { 1207 ex->handlerCount--; 1208 } 1209 1210 if (ex->handlerCount == 0) 1211 { 1212 globals->caughtExceptions = ex->nextException; 1213 if (deleteException) 1214 { 1215 releaseException(ex); 1216 } 1217 } 1218} 1219 1220/** 1221 * ABI function. Returns the type of the current exception. 1222 */ 1223extern "C" std::type_info *__cxa_current_exception_type() 1224{ 1225 __cxa_eh_globals *globals = __cxa_get_globals(); 1226 __cxa_exception *ex = globals->caughtExceptions; 1227 return ex ? ex->exceptionType : 0; 1228} 1229 1230/** 1231 * ABI function, called when an exception specification is violated. 1232 * 1233 * This function does not return. 1234 */ 1235extern "C" void __cxa_call_unexpected(void*exception) 1236{ 1237 _Unwind_Exception *exceptionObject = (_Unwind_Exception*)exception; 1238 if (exceptionObject->exception_class == exception_class) 1239 { 1240 __cxa_exception *ex = exceptionFromPointer(exceptionObject); 1241 if (ex->unexpectedHandler) 1242 { 1243 ex->unexpectedHandler(); 1244 // Should not be reached. 1245 abort(); 1246 } 1247 } 1248 std::unexpected(); 1249 // Should not be reached. 1250 abort(); 1251} 1252 1253/** 1254 * ABI function, returns the adjusted pointer to the exception object. 1255 */ 1256extern "C" void *__cxa_get_exception_ptr(void *exceptionObject) 1257{ 1258 return exceptionFromPointer(exceptionObject)->adjustedPtr; 1259} 1260 1261/** 1262 * As an extension, we provide the ability for the unexpected and terminate 1263 * handlers to be thread-local. We default to the standards-compliant 1264 * behaviour where they are global. 1265 */ 1266static bool thread_local_handlers = false; 1267 1268 1269namespace pathscale 1270{ 1271 /** 1272 * Sets whether unexpected and terminate handlers should be thread-local. 1273 */ 1274 void set_use_thread_local_handlers(bool flag) throw() 1275 { 1276 thread_local_handlers = flag; 1277 } 1278 /** 1279 * Sets a thread-local unexpected handler. 1280 */ 1281 unexpected_handler set_unexpected(unexpected_handler f) throw() 1282 { 1283 static __cxa_thread_info *info = thread_info(); 1284 unexpected_handler old = info->unexpectedHandler; 1285 info->unexpectedHandler = f; 1286 return old; 1287 } 1288 /** 1289 * Sets a thread-local terminate handler. 1290 */ 1291 terminate_handler set_terminate(terminate_handler f) throw() 1292 { 1293 static __cxa_thread_info *info = thread_info(); 1294 terminate_handler old = info->terminateHandler; 1295 info->terminateHandler = f; 1296 return old; 1297 } 1298} 1299 1300namespace std 1301{ 1302 /** 1303 * Sets the function that will be called when an exception specification is 1304 * violated. 1305 */ 1306 unexpected_handler set_unexpected(unexpected_handler f) throw() 1307 { 1308 if (thread_local_handlers) { return pathscale::set_unexpected(f); } 1309 1310 return __sync_lock_test_and_set(&unexpectedHandler, f); 1311 } 1312 /** 1313 * Sets the function that is called to terminate the program. 1314 */ 1315 terminate_handler set_terminate(terminate_handler f) throw() 1316 { 1317 if (thread_local_handlers) { return pathscale::set_terminate(f); } 1318 return __sync_lock_test_and_set(&terminateHandler, f); 1319 } 1320 /** 1321 * Terminates the program, calling a custom terminate implementation if 1322 * required. 1323 */ 1324 void terminate() 1325 { 1326 static __cxa_thread_info *info = thread_info_fast(); 1327 if (0 != info && 0 != info->terminateHandler) 1328 { 1329 info->terminateHandler(); 1330 // Should not be reached - a terminate handler is not expected to 1331 // return. 1332 abort(); 1333 } 1334 terminateHandler(); 1335 } 1336 /** 1337 * Called when an unexpected exception is encountered (i.e. an exception 1338 * violates an exception specification). This calls abort() unless a 1339 * custom handler has been set.. 1340 */ 1341 void unexpected() 1342 { 1343 static __cxa_thread_info *info = thread_info_fast(); 1344 if (0 != info && 0 != info->unexpectedHandler) 1345 { 1346 info->unexpectedHandler(); 1347 // Should not be reached - a terminate handler is not expected to 1348 // return. 1349 abort(); 1350 } 1351 unexpectedHandler(); 1352 } 1353 /** 1354 * Returns whether there are any exceptions currently being thrown that 1355 * have not been caught. This can occur inside a nested catch statement. 1356 */ 1357 bool uncaught_exception() throw() 1358 { 1359 __cxa_thread_info *info = thread_info(); 1360 return info->globals.uncaughtExceptions != 0; 1361 } 1362 /** 1363 * Returns the current unexpected handler. 1364 */ 1365 unexpected_handler get_unexpected() throw() 1366 { 1367 __cxa_thread_info *info = thread_info(); 1368 if (info->unexpectedHandler) 1369 { 1370 return info->unexpectedHandler; 1371 } 1372 return unexpectedHandler; 1373 } 1374 /** 1375 * Returns the current terminate handler. 1376 */ 1377 terminate_handler get_terminate() throw() 1378 { 1379 __cxa_thread_info *info = thread_info(); 1380 if (info->terminateHandler) 1381 { 1382 return info->terminateHandler; 1383 } 1384 return terminateHandler; 1385 } 1386} 1387#ifdef __arm__ 1388extern "C" _Unwind_Exception *__cxa_get_cleanup(void) 1389{ 1390 __cxa_thread_info *info = thread_info_fast(); 1391 _Unwind_Exception *exceptionObject = info->currentCleanup; 1392 if (isCXXException(exceptionObject->exception_class)) 1393 { 1394 __cxa_exception *ex = exceptionFromPointer(exceptionObject); 1395 ex->cleanupCount--; 1396 if (ex->cleanupCount == 0) 1397 { 1398 info->currentCleanup = ex->nextCleanup; 1399 ex->nextCleanup = 0; 1400 } 1401 } 1402 else 1403 { 1404 info->currentCleanup = 0; 1405 } 1406 return exceptionObject; 1407} 1408 1409asm ( 1410".pushsection .text.__cxa_end_cleanup \n" 1411".global __cxa_end_cleanup \n" 1412".type __cxa_end_cleanup, \"function\" \n" 1413"__cxa_end_cleanup: \n" 1414" push {r1, r2, r3, r4} \n" 1415" bl __cxa_get_cleanup \n" 1416" push {r1, r2, r3, r4} \n" 1417" b _Unwind_Resume \n" 1418" bl abort \n" 1419".popsection \n" 1420); 1421#endif 1422