IOS开发如何通过覆盖问题来解决捕获信号处理程序

Question

我想让项目中现有的单一处理程序和我自己的单一处理程序共存，这样两者都可以正确地捕获单数。

typedef void (*signalHandler)(int signo, siginfo_t *info, void *context);
static signalHandler previousSignalHandler = NULL;
void signalExceptionHandler(int signal, siginfo_t* info, void* context)
{
    NSMutableString *mstr = [[NSMutableString alloc] init];
    [mstr appendString:@"Stack:\n"];
    void* callstack[128];
    int i, frames = backtrace(callstack, 128);
    char** strs = backtrace_symbols(callstack, frames);
    for (i = 0; i <frames; ++i) {
        [mstr appendFormat:@"%s\n", strs[i]];
    }
    BYLOGI(@"%@",mstr);
    [BYCrashCacheHelper saveAppCrashDataWithCrashInfo:mstr];
    if (previousSignalHandler) {
        previousSignalHandler(signal, info, context);
    }
}
void signalRegister(int signal)
{
    struct sigaction action;
    action.sa_sigaction = signalExceptionHandler;
    action.sa_flags = SA_NODEFER | SA_SIGINFO;
    sigemptyset(&action.sa_mask);
    sigaction(signal, &action, 0);
}
void judgePreviousSignalHandlerAndSignalRegister(int signal)
{
    struct sigaction old_action;
    sigaction(signal, NULL, &old_action);
    if (old_action.sa_flags & SA_SIGINFO) {
        previousSignalHandler = old_action.sa_sigaction;
    }
    signalRegister(signal);
}
void installSignalHandler(void)
{
    judgePreviousSignalHandlerAndSignalRegister(SIGHUP);
    judgePreviousSignalHandlerAndSignalRegister(SIGINT);
    judgePreviousSignalHandlerAndSignalRegister(SIGQUIT);

    judgePreviousSignalHandlerAndSignalRegister(SIGABRT);
    judgePreviousSignalHandlerAndSignalRegister(SIGILL);
    judgePreviousSignalHandlerAndSignalRegister(SIGSEGV);
    judgePreviousSignalHandlerAndSignalRegister(SIGFPE);
    judgePreviousSignalHandlerAndSignalRegister(SIGBUS);
    judgePreviousSignalHandlerAndSignalRegister(SIGPIPE);
}

我在一些博客中找到了上述方法，但经过调试后，我发现它无法访问上一个处理程序。 对不起，如何正确获取前一个处理程序，并避免处理程序覆盖问题？