util/ios/exception_processor.mm - third_party/crashpad - Git at Google

 // Copyright 2020 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 #include "util/ios/exception_processor.h"

 #import <Foundation/Foundation.h>
 #include <TargetConditionals.h>
 #include <cxxabi.h>
 #include <dlfcn.h>
 #include <libunwind.h>
 #include <mach-o/loader.h>
 #include <objc/message.h>
 #include <objc/objc-exception.h>
 #include <objc/objc.h>
 #include <objc/runtime.h>
 #include <stdint.h>
 #include <string.h>
 #include <sys/types.h>
 #include <unwind.h>

 #include <exception>
 #include <type_traits>
 #include <typeinfo>

 #include "base/bit_cast.h"
 #include "base/logging.h"
 #include "base/strings/sys_string_conversions.h"
 #include "build/build_config.h"

 namespace {

 // From 10.15.0 objc4-779.1/runtime/objc-exception.mm.
 struct objc_typeinfo {
   const void* const* vtable;
   const char* name;
   Class cls_unremapped;
 };
 struct objc_exception {
   id obj;
   objc_typeinfo tinfo;
 };

 // From 10.15.0 objc4-779.1/runtime/objc-abi.h.
 extern "C" const void* const objc_ehtype_vtable[];

 // https://github.com/llvm/llvm-project/blob/09dc884eb2e4/libcxxabi/src/cxa_exception.h
 static const uint64_t kOurExceptionClass = 0x434c4e47432b2b00;
 struct __cxa_exception {
 #if defined(ARCH_CPU_64_BITS)
   void* reserve;
   size_t referenceCount;
 #endif
   std::type_info* exceptionType;
   void (*exceptionDestructor)(void*);
   std::unexpected_handler unexpectedHandler;
   std::terminate_handler terminateHandler;
   __cxa_exception* nextException;
   int handlerCount;
   int handlerSwitchValue;
   const unsigned char* actionRecord;
   const unsigned char* languageSpecificData;
   void* catchTemp;
   void* adjustedPtr;
 #if !defined(ARCH_CPU_64_BITS)
   size_t referenceCount;
 #endif
   _Unwind_Exception unwindHeader;
 };

 objc_exception_preprocessor g_next_preprocessor;
 bool g_exception_preprocessor_installed;

 void TerminatingFromUncaughtNSException(id exception, const char* sinkhole) {
   // TODO(justincohen): This is incomplete, as the signal handler will not have
   // access to the exception name and reason.  Pass that along somehow here.
   NSString* exception_message_ns = [NSString
       stringWithFormat:@"%@: %@", [exception name], [exception reason]];
   std::string exception_message = base::SysNSStringToUTF8(exception_message_ns);
   LOG(INFO) << "Terminating from Objective-C exception: " << exception_message
             << " with sinkhole: " << sinkhole;
   // TODO(justincohen): This is temporary, as crashpad can capture this
   // exception directly instead.
   std::terminate();
 }

 // Returns true if |path| equals |sinkhole| on device. Simulator paths prepend
 // much of Xcode's internal structure, so check that |path| ends with |sinkhole|
 // for simulator.
 bool ModulePathMatchesSinkhole(const char* path, const char* sinkhole) {
 #if TARGET_OS_SIMULATOR
   size_t path_length = strlen(path);
   size_t sinkhole_length = strlen(sinkhole);
   if (sinkhole_length > path_length)
     return false;
   return strncmp(path + path_length - sinkhole_length,
                  sinkhole,
                  sinkhole_length) == 0;
 #else
   return strcmp(path, sinkhole) == 0;
 #endif
 }

 int LoggingUnwStep(unw_cursor_t* cursor) {
   int rv = unw_step(cursor);
   if (rv < 0) {
     LOG(ERROR) << "unw_step: " << rv;
   }
   return rv;
 }

 id ObjcExceptionPreprocessor(id exception) {
   // Unwind the stack looking for any exception handlers. If an exception
   // handler is encountered, test to see if it is a function known to catch-
   // and-rethrow as a "top-level" exception handler. Various routines in
   // Cocoa/UIKit do this, and it obscures the crashing stack, since the original
   // throw location is no longer present on the stack (just the re-throw) when
   // Crashpad captures the crash report.
   unw_context_t context;
   unw_getcontext(&context);

   unw_cursor_t cursor;
   unw_init_local(&cursor, &context);

   static const void* this_base_address = []() -> const void* {
     Dl_info dl_info;
     if (!dladdr(reinterpret_cast<const void*>(&ObjcExceptionPreprocessor),
                 &dl_info)) {
       LOG(ERROR) << "dladdr: " << dlerror();
       return nullptr;
     }
     return dl_info.dli_fbase;
   }();

   // Generate an exception_header for the __personality_routine.
   // From 10.15.0 objc4-779.1/runtime/objc-exception.mm objc_exception_throw.
   objc_exception* exception_objc = reinterpret_cast<objc_exception*>(
       __cxxabiv1::__cxa_allocate_exception(sizeof(objc_exception)));
   exception_objc->obj = exception;
   exception_objc->tinfo.vtable = objc_ehtype_vtable + 2;
   exception_objc->tinfo.name = object_getClassName(exception);
   exception_objc->tinfo.cls_unremapped = object_getClass(exception);

   // https://github.com/llvm/llvm-project/blob/c5d2746fbea7/libcxxabi/src/cxa_exception.cpp
   // __cxa_throw
   __cxa_exception* exception_header =
       reinterpret_cast<__cxa_exception*>(exception_objc) - 1;
   exception_header->unexpectedHandler = std::get_unexpected();
   exception_header->terminateHandler = std::get_terminate();
   exception_header->exceptionType =
       reinterpret_cast<std::type_info*>(&exception_objc->tinfo);
   exception_header->unwindHeader.exception_class = kOurExceptionClass;

   bool handler_found = false;
   while (LoggingUnwStep(&cursor) > 0) {
     unw_proc_info_t frame_info;
     if (unw_get_proc_info(&cursor, &frame_info) != UNW_ESUCCESS) {
       continue;
     }

     if (frame_info.handler == 0) {
       continue;
     }

     // Check to see if the handler is really an exception handler.
     __personality_routine p =
         reinterpret_cast<__personality_routine>(frame_info.handler);

     // From 10.15.0 libunwind-35.4/src/UnwindLevel1.c.
     _Unwind_Reason_Code personalityResult = (*p)(
         1,
         _UA_SEARCH_PHASE,
         exception_header->unwindHeader.exception_class,
         reinterpret_cast<_Unwind_Exception*>(&exception_header->unwindHeader),
         reinterpret_cast<_Unwind_Context*>(&cursor));
     switch (personalityResult) {
       case _URC_HANDLER_FOUND:
         break;
       case _URC_CONTINUE_UNWIND:
         continue;
       default:
         break;
     }

     char proc_name[512];
     unw_word_t offset;
     if (unw_get_proc_name(&cursor, proc_name, sizeof(proc_name), &offset) !=
         UNW_ESUCCESS) {
       // The symbol has no name, so see if it belongs to the same image as
       // this function.
       Dl_info dl_info;
       if (dladdr(reinterpret_cast<const void*>(frame_info.start_ip),
                  &dl_info)) {
         if (dl_info.dli_fbase == this_base_address) {
           // This is a handler in our image, so allow it to run.
           handler_found = true;
           break;
         }
       }

       // This handler does not belong to us, so continue the search.
       continue;
     }

     // Check if the function is one that is known to obscure (by way of
     // catch-and-rethrow) exception stack traces. If it is, sinkhole it
     // by crashing here at the point of throw.
     constexpr const char* kExceptionSymbolNameSinkholes[] = {
         // The two CF symbol names will also be captured by the CoreFoundation
         // library path check below, but for completeness they are listed here,
         // since they appear unredacted.
         "CFRunLoopRunSpecific",
         "_CFXNotificationPost",
         "__NSFireDelayedPerform",
     };
     for (const char* sinkhole : kExceptionSymbolNameSinkholes) {
       if (strcmp(sinkhole, proc_name) == 0) {
         TerminatingFromUncaughtNSException(exception, sinkhole);
       }
     }

     // On iOS, function names are often reported as "<redacted>", although they
     // do appear when attached to the debugger.  When this happens, use the path
     // of the image to determine if the handler is an exception sinkhole.
     constexpr const char* kExceptionLibraryPathSinkholes[] = {
         // Everything in this library is a sinkhole, specifically
         // _dispatch_client_callout.  Both are needed here depending on whether
         // the debugger is attached (introspection only appears when a simulator
         // is attached to a debugger).
         "/usr/lib/system/introspection/libdispatch.dylib",
         "/usr/lib/system/libdispatch.dylib",

         // __CFRunLoopDoTimers and __CFRunLoopRun are sinkholes. Consider also
         // checking that a few frames up is CFRunLoopRunSpecific().
         "/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation",
     };

     Dl_info dl_info;
     if (dladdr(reinterpret_cast<const void*>(frame_info.start_ip), &dl_info) !=
         0) {
       for (const char* sinkhole : kExceptionLibraryPathSinkholes) {
         if (ModulePathMatchesSinkhole(dl_info.dli_fname, sinkhole)) {
           TerminatingFromUncaughtNSException(exception, sinkhole);
         }
       }
     }

     // Some <redacted> sinkholes are harder to find. _UIGestureEnvironmentUpdate
     // in UIKitCore is an example. UIKitCore can't be added to
     // kExceptionLibraryPathSinkholes because it uses Objective-C exceptions
     // internally and also has has non-sinkhole handlers. Since
     // _UIGestureEnvironmentUpdate is always called from
     // -[UIGestureEnvironment _deliverEvent:toGestureRecognizers:usingBlock:],
     // inspect the caller frame info to match the sinkhole.
     constexpr const char* kUIKitCorePath =
         "/System/Library/PrivateFrameworks/UIKitCore.framework/UIKitCore";
     if (ModulePathMatchesSinkhole(dl_info.dli_fname, kUIKitCorePath)) {
       unw_proc_info_t caller_frame_info;
       if (LoggingUnwStep(&cursor) > 0 &&
           unw_get_proc_info(&cursor, &caller_frame_info) == UNW_ESUCCESS) {
         static IMP uigesture_deliver_event_imp = [] {
           IMP imp = class_getMethodImplementation(
               NSClassFromString(@"UIGestureEnvironment"),
               NSSelectorFromString(
                   @"_deliverEvent:toGestureRecognizers:usingBlock:"));

           // From 10.15.0 objc4-779.1/runtime/objc-class.mm
           // class_getMethodImplementation returns nil or _objc_msgForward on
           // failure.
           if (!imp || imp == _objc_msgForward) {
             LOG(WARNING) << "Unable to find -[UIGestureEnvironment "
                             "_deliverEvent:toGestureRecognizers:usingBlock:]";
             return bit_cast<IMP>(nullptr);  // IMP is a function pointer type.
           }
           return imp;
         }();

         if (uigesture_deliver_event_imp ==
             reinterpret_cast<IMP>(caller_frame_info.start_ip)) {
           TerminatingFromUncaughtNSException(exception,
                                              "_UIGestureEnvironmentUpdate");
         }
       }
     }

     handler_found = true;

     break;
   }

   // If no handler is found, __cxa_throw would call failed_throw and terminate.
   // See:
   // https://github.com/llvm/llvm-project/blob/c5d2746fbea7/libcxxabi/src/cxa_exception.cpp
   // __cxa_throw. Instead, terminate via TerminatingFromUncaughtNSException so
   // the exception name and reason are properly recorded.
   if (!handler_found) {
     TerminatingFromUncaughtNSException(exception, "__cxa_throw");
   }

   // Forward to the next preprocessor.
   if (g_next_preprocessor)
     return g_next_preprocessor(exception);

   return exception;
 }

 }  // namespace

 namespace crashpad {

 void InstallObjcExceptionPreprocessor() {
   DCHECK(!g_exception_preprocessor_installed);

   g_next_preprocessor =
       objc_setExceptionPreprocessor(&ObjcExceptionPreprocessor);
   g_exception_preprocessor_installed = true;
 }

 void UninstallObjcExceptionPreprocessor() {
   DCHECK(g_exception_preprocessor_installed);

   objc_setExceptionPreprocessor(g_next_preprocessor);
   g_next_preprocessor = nullptr;
   g_exception_preprocessor_installed = false;
 }

 }  // namespace crashpad
	// Copyright 2020 The Crashpad Authors. All rights reserved.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	#include "util/ios/exception_processor.h"

	#import <Foundation/Foundation.h>
	#include <TargetConditionals.h>
	#include <cxxabi.h>
	#include <dlfcn.h>
	#include <libunwind.h>
	#include <mach-o/loader.h>
	#include <objc/message.h>
	#include <objc/objc-exception.h>
	#include <objc/objc.h>
	#include <objc/runtime.h>
	#include <stdint.h>
	#include <string.h>
	#include <sys/types.h>
	#include <unwind.h>

	#include <exception>
	#include <type_traits>
	#include <typeinfo>

	#include "base/bit_cast.h"
	#include "base/logging.h"
	#include "base/strings/sys_string_conversions.h"
	#include "build/build_config.h"

	namespace {

	// From 10.15.0 objc4-779.1/runtime/objc-exception.mm.
	struct objc_typeinfo {
	const void* const* vtable;
	const char* name;
	Class cls_unremapped;
	};
	struct objc_exception {
	id obj;
	objc_typeinfo tinfo;
	};

	// From 10.15.0 objc4-779.1/runtime/objc-abi.h.
	extern "C" const void* const objc_ehtype_vtable[];

	// https://github.com/llvm/llvm-project/blob/09dc884eb2e4/libcxxabi/src/cxa_exception.h
	static const uint64_t kOurExceptionClass = 0x434c4e47432b2b00;
	struct __cxa_exception {
	#if defined(ARCH_CPU_64_BITS)
	void* reserve;
	size_t referenceCount;
	#endif
	std::type_info* exceptionType;
	void (exceptionDestructor)(void);
	std::unexpected_handler unexpectedHandler;
	std::terminate_handler terminateHandler;
	__cxa_exception* nextException;
	int handlerCount;
	int handlerSwitchValue;
	const unsigned char* actionRecord;
	const unsigned char* languageSpecificData;
	void* catchTemp;
	void* adjustedPtr;
	#if !defined(ARCH_CPU_64_BITS)
	size_t referenceCount;
	#endif
	_Unwind_Exception unwindHeader;
	};

	objc_exception_preprocessor g_next_preprocessor;
	bool g_exception_preprocessor_installed;

	void TerminatingFromUncaughtNSException(id exception, const char* sinkhole) {
	// TODO(justincohen): This is incomplete, as the signal handler will not have
	// access to the exception name and reason. Pass that along somehow here.
	NSString* exception_message_ns = [NSString
	stringWithFormat:@"%@: %@", [exception name], [exception reason]];
	std::string exception_message = base::SysNSStringToUTF8(exception_message_ns);
	LOG(INFO) << "Terminating from Objective-C exception: " << exception_message
	<< " with sinkhole: " << sinkhole;
	// TODO(justincohen): This is temporary, as crashpad can capture this
	// exception directly instead.
	std::terminate();
	}

	// Returns true if \|path\| equals \|sinkhole\| on device. Simulator paths prepend
	// much of Xcode's internal structure, so check that \|path\| ends with \|sinkhole\|
	// for simulator.
	bool ModulePathMatchesSinkhole(const char* path, const char* sinkhole) {
	#if TARGET_OS_SIMULATOR
	size_t path_length = strlen(path);
	size_t sinkhole_length = strlen(sinkhole);
	if (sinkhole_length > path_length)
	return false;
	return strncmp(path + path_length - sinkhole_length,
	sinkhole,
	sinkhole_length) == 0;
	#else
	return strcmp(path, sinkhole) == 0;
	#endif
	}

	int LoggingUnwStep(unw_cursor_t* cursor) {
	int rv = unw_step(cursor);
	if (rv < 0) {
	LOG(ERROR) << "unw_step: " << rv;
	}
	return rv;
	}

	id ObjcExceptionPreprocessor(id exception) {
	// Unwind the stack looking for any exception handlers. If an exception
	// handler is encountered, test to see if it is a function known to catch-
	// and-rethrow as a "top-level" exception handler. Various routines in
	// Cocoa/UIKit do this, and it obscures the crashing stack, since the original
	// throw location is no longer present on the stack (just the re-throw) when
	// Crashpad captures the crash report.
	unw_context_t context;
	unw_getcontext(&context);

	unw_cursor_t cursor;
	unw_init_local(&cursor, &context);

	static const void* this_base_address = []() -> const void* {
	Dl_info dl_info;
	if (!dladdr(reinterpret_cast<const void*>(&ObjcExceptionPreprocessor),
	&dl_info)) {
	LOG(ERROR) << "dladdr: " << dlerror();
	return nullptr;
	}
	return dl_info.dli_fbase;
	}();

	// Generate an exception_header for the __personality_routine.
	// From 10.15.0 objc4-779.1/runtime/objc-exception.mm objc_exception_throw.
	objc_exception* exception_objc = reinterpret_cast<objc_exception*>(
	__cxxabiv1::__cxa_allocate_exception(sizeof(objc_exception)));
	exception_objc->obj = exception;
	exception_objc->tinfo.vtable = objc_ehtype_vtable + 2;
	exception_objc->tinfo.name = object_getClassName(exception);
	exception_objc->tinfo.cls_unremapped = object_getClass(exception);

	// https://github.com/llvm/llvm-project/blob/c5d2746fbea7/libcxxabi/src/cxa_exception.cpp
	// __cxa_throw
	__cxa_exception* exception_header =
	reinterpret_cast<__cxa_exception*>(exception_objc) - 1;
	exception_header->unexpectedHandler = std::get_unexpected();
	exception_header->terminateHandler = std::get_terminate();
	exception_header->exceptionType =
	reinterpret_cast<std::type_info*>(&exception_objc->tinfo);
	exception_header->unwindHeader.exception_class = kOurExceptionClass;

	bool handler_found = false;
	while (LoggingUnwStep(&cursor) > 0) {
	unw_proc_info_t frame_info;
	if (unw_get_proc_info(&cursor, &frame_info) != UNW_ESUCCESS) {
	continue;
	}

	if (frame_info.handler == 0) {
	continue;
	}

	// Check to see if the handler is really an exception handler.
	__personality_routine p =
	reinterpret_cast<__personality_routine>(frame_info.handler);

	// From 10.15.0 libunwind-35.4/src/UnwindLevel1.c.
	_Unwind_Reason_Code personalityResult = (*p)(
	1,
	_UA_SEARCH_PHASE,
	exception_header->unwindHeader.exception_class,
	reinterpret_cast<_Unwind_Exception*>(&exception_header->unwindHeader),
	reinterpret_cast<_Unwind_Context*>(&cursor));
	switch (personalityResult) {
	case _URC_HANDLER_FOUND:
	break;
	case _URC_CONTINUE_UNWIND:
	continue;
	default:
	break;
	}

	char proc_name[512];
	unw_word_t offset;
	if (unw_get_proc_name(&cursor, proc_name, sizeof(proc_name), &offset) !=
	UNW_ESUCCESS) {
	// The symbol has no name, so see if it belongs to the same image as
	// this function.
	Dl_info dl_info;
	if (dladdr(reinterpret_cast<const void*>(frame_info.start_ip),
	&dl_info)) {
	if (dl_info.dli_fbase == this_base_address) {
	// This is a handler in our image, so allow it to run.
	handler_found = true;
	break;
	}
	}

	// This handler does not belong to us, so continue the search.
	continue;
	}

	// Check if the function is one that is known to obscure (by way of
	// catch-and-rethrow) exception stack traces. If it is, sinkhole it
	// by crashing here at the point of throw.
	constexpr const char* kExceptionSymbolNameSinkholes[] = {
	// The two CF symbol names will also be captured by the CoreFoundation
	// library path check below, but for completeness they are listed here,
	// since they appear unredacted.
	"CFRunLoopRunSpecific",
	"_CFXNotificationPost",
	"__NSFireDelayedPerform",
	};
	for (const char* sinkhole : kExceptionSymbolNameSinkholes) {
	if (strcmp(sinkhole, proc_name) == 0) {
	TerminatingFromUncaughtNSException(exception, sinkhole);
	}
	}

	// On iOS, function names are often reported as "<redacted>", although they
	// do appear when attached to the debugger. When this happens, use the path
	// of the image to determine if the handler is an exception sinkhole.
	constexpr const char* kExceptionLibraryPathSinkholes[] = {
	// Everything in this library is a sinkhole, specifically
	// _dispatch_client_callout. Both are needed here depending on whether
	// the debugger is attached (introspection only appears when a simulator
	// is attached to a debugger).
	"/usr/lib/system/introspection/libdispatch.dylib",
	"/usr/lib/system/libdispatch.dylib",

	// __CFRunLoopDoTimers and __CFRunLoopRun are sinkholes. Consider also
	// checking that a few frames up is CFRunLoopRunSpecific().
	"/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation",
	};

	Dl_info dl_info;
	if (dladdr(reinterpret_cast<const void*>(frame_info.start_ip), &dl_info) !=
	0) {
	for (const char* sinkhole : kExceptionLibraryPathSinkholes) {
	if (ModulePathMatchesSinkhole(dl_info.dli_fname, sinkhole)) {
	TerminatingFromUncaughtNSException(exception, sinkhole);
	}
	}
	}

	// Some <redacted> sinkholes are harder to find. _UIGestureEnvironmentUpdate
	// in UIKitCore is an example. UIKitCore can't be added to
	// kExceptionLibraryPathSinkholes because it uses Objective-C exceptions
	// internally and also has has non-sinkhole handlers. Since
	// _UIGestureEnvironmentUpdate is always called from
	// -[UIGestureEnvironment _deliverEvent:toGestureRecognizers:usingBlock:],
	// inspect the caller frame info to match the sinkhole.
	constexpr const char* kUIKitCorePath =
	"/System/Library/PrivateFrameworks/UIKitCore.framework/UIKitCore";
	if (ModulePathMatchesSinkhole(dl_info.dli_fname, kUIKitCorePath)) {
	unw_proc_info_t caller_frame_info;
	if (LoggingUnwStep(&cursor) > 0 &&
	unw_get_proc_info(&cursor, &caller_frame_info) == UNW_ESUCCESS) {
	static IMP uigesture_deliver_event_imp = [] {
	IMP imp = class_getMethodImplementation(
	NSClassFromString(@"UIGestureEnvironment"),
	NSSelectorFromString(
	@"_deliverEvent:toGestureRecognizers:usingBlock:"));

	// From 10.15.0 objc4-779.1/runtime/objc-class.mm
	// class_getMethodImplementation returns nil or _objc_msgForward on
	// failure.
	if (!imp \|\| imp == _objc_msgForward) {
	LOG(WARNING) << "Unable to find -[UIGestureEnvironment "
	"_deliverEvent:toGestureRecognizers:usingBlock:]";
	return bit_cast<IMP>(nullptr); // IMP is a function pointer type.
	}
	return imp;
	}();

	if (uigesture_deliver_event_imp ==
	reinterpret_cast<IMP>(caller_frame_info.start_ip)) {
	TerminatingFromUncaughtNSException(exception,
	"_UIGestureEnvironmentUpdate");
	}
	}
	}

	handler_found = true;

	break;
	}

	// If no handler is found, __cxa_throw would call failed_throw and terminate.
	// See:
	// https://github.com/llvm/llvm-project/blob/c5d2746fbea7/libcxxabi/src/cxa_exception.cpp
	// __cxa_throw. Instead, terminate via TerminatingFromUncaughtNSException so
	// the exception name and reason are properly recorded.
	if (!handler_found) {
	TerminatingFromUncaughtNSException(exception, "__cxa_throw");
	}

	// Forward to the next preprocessor.
	if (g_next_preprocessor)
	return g_next_preprocessor(exception);

	return exception;
	}

	} // namespace

	namespace crashpad {

	void InstallObjcExceptionPreprocessor() {
	DCHECK(!g_exception_preprocessor_installed);

	g_next_preprocessor =
	objc_setExceptionPreprocessor(&ObjcExceptionPreprocessor);
	g_exception_preprocessor_installed = true;
	}

	void UninstallObjcExceptionPreprocessor() {
	DCHECK(g_exception_preprocessor_installed);

	objc_setExceptionPreprocessor(g_next_preprocessor);
	g_next_preprocessor = nullptr;
	g_exception_preprocessor_installed = false;
	}

	} // namespace crashpad