信号学习心得 如何模拟发信号给进程

系统调用
SYSCALL_DEFINE4(rt_sigprocmask, int, how, sigset_t __user *, nset,
sigset_t __user *, oset, size_t, sigsetsize) //堵塞或者撤销堵塞某些信号
=>sigprocmask
SYSCALL_DEFINE3(sigprocmask, int, how, old_sigset_t __user *, nset,
old_sigset_t __user *, oset)
=>sigaddsetmask(&new_blocked, new_set);

SYSCALL_DEFINE2(signal, int, sig, __sighandler_t, handler)//设置信号处理函数
=>do_sigaction(sig, &new_sa, &old_sa);

内核信号触发，详见LINUX内存管理部分，do_page_fault

内核信号处理
do_notify_resume
=>do_signal
=>signr = get_signal_to_deliver(&info, &ka, regs, NULL);
=>for (;;)
=>signr = dequeue_signal(current, ¤t->blocked, info);//pending队列取一个信号
=>if (!signr)//队列为空时退出
break; /* will return 0 */
=>if (ka->sa.sa_handler != SIG_DFL) {//如果不是默认信号处理函数则退出
/* Run the handler.  */
*return_ka = *ka;

if (ka->sa.sa_flags & SA_ONESHOT)
ka->sa.sa_handler = SIG_DFL;

break; /* will return non-zero "signr" value */
}
=>if (sig_kernel_coredump(signr))//如果信号比较严重，则coredump，增加调试信息
do_coredump(info->si_signo, info->si_signo, regs);
=>retval = binfmt->core_dump(&cprm);
static struct linux_binfmt elf_format = {
.module     = THIS_MODULE,
.load_binary    = load_elf_binary,
.load_shlib = load_elf_library,
.core_dump  = elf_core_dump,
.min_coredump   = ELF_EXEC_PAGESIZE,
};
#ifdef CONFIG_ELF_CORE
static int elf_core_dump(struct coredump_params *cprm);
#else
#define elf_core_dump   NULL
#endif
=>do_group_exit(info->si_signo);
=>handle_signal(signr, &info, &ka, oldset, regs)
=>ret = abi->setup_rt_frame(vdso + abi->rt_signal_return_offset, ka, regs, sig, oldset, info);
=>setup_rt_frame //arch\mips\kernel):   .setup_rt_frame = setup_rt_frame,
=>frame = get_sigframe(ka, regs, sizeof(*frame));
=>/* Create siginfo.  */
err |= copy_siginfo_to_user(&frame->rs_info, info);//设置信号处理函数栈帧
=>regs->cp0_epc = regs->regs[25] = (unsigned long) ka->sa.sa_handler;//挂接信号处理函数，handle_signal返回时调用sa_handler

内核在允许进程恢复用户态执行之前，检测进程TIF_SIGPENDING标志的数值，每当内核处理完1个中断/异常时，就检查是否存在进程挂起信号

文章参考

http://www.cnblogs.com/hoys/archive/2012/08/19/2646377.html

监控进程：可以通过epoll与所有进程通信，一旦通信是吧，可以调用waitpid获取状态

如何模拟发信号给进程

https://www.cnblogs.com/itech/archive/2012/03/05/2380794.html

利用sigpending,sigismember检测信号是否被挂起

http://blog.csdn.net/he_0123/article/details/46584971

该篇文章讲SIGINT替换成SIGILL，然后将main函数的主体增加while {sleep(1);} ；做实验kill -ILL 进程号，内核会进入do_signal函数

void do_notify_resume(struct pt_regs *regs, void *_unused,
__u32 thread_info_flags)
{
/* Pending single-step? */
if (thread_info_flags & _TIF_SINGLESTEP) {
regs->eflags |= TF_MASK;
clear_thread_flag(TIF_SINGLESTEP);
}

/* deal with pending signal delivery */
if (thread_info_flags & (_TIF_SIGPENDING | _TIF_RESTORE_SIGMASK))
do_signal(regs);
=>handle_signal(signr, &info, &ka, oldset, regs)
=>ret = setup_frame(sig, ka, oldset, regs);
=>printk("SIG deliver (%s:%d): sp=%p pc=%p ra=%p\n", current->comm, current->pid, frame, regs->eip, frame->pretcode);

clear_thread_flag(TIF_IRET);
}