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// Copyright 2016 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/40285824): Remove this and convert code to safer constructs.
#pragma allow_unsafe_buffers
#endif
#import "chrome/browser/mac/exception_processor.h"
#import <Foundation/Foundation.h>
#include <dlfcn.h>
#include <libunwind.h>
#include <objc/objc-exception.h>
#include <type_traits>
#include "base/compiler_specific.h"
#include "base/debug/crash_logging.h"
#include "base/debug/stack_trace.h"
#include "base/feature_list.h"
#include "base/logging.h"
#include "base/strings/sys_string_conversions.h"
#include "components/crash/core/common/crash_key.h"
static objc_exception_preprocessor g_next_preprocessor = nullptr;
// It is believed that crashing on exceptions is breaking bucketing on the crash
// server; see the analysis on https://crbug.com/358138966. Disable it by
// default for now, while leaving an emergency re-enablement switch, and remove
// it entirely in a few releases.
BASE_FEATURE(kForceCrashOnExceptions,
"ForceCrashOnExceptions",
base::FEATURE_DISABLED_BY_DEFAULT);
static const char* const kExceptionSinkholes[] = {
"CFRunLoopRunSpecific",
"_CFXNotificationPost",
"__CFRunLoopRun",
"__NSFireDelayedPerform",
"_dispatch_client_callout",
};
// This function is used to make it clear to the crash processor that this is
// a forced exception crash.
NOINLINE static void TERMINATING_FROM_UNCAUGHT_NSEXCEPTION(id exception) {
NSString* exception_message_ns = [NSString
stringWithFormat:@"%@: %@", [exception name], [exception reason]];
std::string exception_message = base::SysNSStringToUTF8(exception_message_ns);
static crash_reporter::CrashKeyString<256> crash_key("nsexception");
crash_key.Set(exception_message);
LOG(FATAL) << "Terminating from Objective-C exception: " << exception_message;
}
static id ObjcExceptionPreprocessor(id exception) {
static bool seen_first_exception = false;
static crash_reporter::CrashKeyString<256> firstexception("firstexception");
static crash_reporter::CrashKeyString<256> lastexception("lastexception");
static crash_reporter::CrashKeyString<1024> firstexception_bt(
"firstexception_bt");
static crash_reporter::CrashKeyString<1024> lastexception_bt(
"lastexception_bt");
auto* key = seen_first_exception ? &lastexception : &firstexception;
auto* bt_key = seen_first_exception ? &lastexception_bt : &firstexception_bt;
NSString* value = [NSString stringWithFormat:@"%@ reason %@",
[exception name], [exception reason]];
key->Set(base::SysNSStringToUTF8(value));
// This exception preprocessor runs prior to the one in libobjc, which sets
// the -[NSException callStackReturnAddresses].
crash_reporter::SetCrashKeyStringToStackTrace(bt_key,
base::debug::StackTrace());
seen_first_exception = true;
if (base::FeatureList::IsEnabled(kForceCrashOnExceptions)) {
// 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 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);
// Get the base address for the image that contains this function.
Dl_info dl_info;
const void* this_base_address = 0;
if (dladdr(reinterpret_cast<const void*>(&ObjcExceptionPreprocessor),
&dl_info) != 0) {
this_base_address = dl_info.dli_fbase;
}
while (unw_step(&cursor) > 0) {
unw_proc_info_t frame_info;
if (unw_get_proc_info(&cursor, &frame_info) != UNW_ESUCCESS) {
continue;
}
// This frame has an exception handler.
if (frame_info.handler != 0) {
char proc_name[64];
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.
if (dladdr(reinterpret_cast<const void*>(frame_info.start_ip),
&dl_info) != 0) {
if (dl_info.dli_fbase == this_base_address) {
// This is a handler in our image, so allow it to run.
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.
for (const char* sinkhole : kExceptionSinkholes) {
if (strcmp(sinkhole, proc_name) == 0) {
TERMINATING_FROM_UNCAUGHT_NSEXCEPTION(exception);
}
}
VLOG(1) << "Stopping search for exception handler at " << proc_name;
break;
}
}
}
// Forward to the next preprocessor.
if (g_next_preprocessor)
return g_next_preprocessor(exception);
return exception;
}
void InstallObjcExceptionPreprocessor() {
if (g_next_preprocessor)
return;
g_next_preprocessor =
objc_setExceptionPreprocessor(&ObjcExceptionPreprocessor);
}
void UninstallObjcExceptionPreprocessor() {
objc_setExceptionPreprocessor(g_next_preprocessor);
g_next_preprocessor = nullptr;
}
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