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在进行系统调用时发生signal的情况下改怎么办呢？ 从kernel中信号量的处理函数do_signal中可以可以看到，通过in_syscall(regs)来判断发生signal的时候是否正在进行系统调用，如果是的话，则暂时忽略掉系统调用，等处理完信号量后再进行系统调用的过程static void do_signal(struct pt_regs *regs){	unsigned long continue_addr = 0, restart_addr = 0;	int retval = 0;	struct ksignal ksig;	/*	 * If we were from a system call, check for system call restarting...	 */#处于系统调用的过程中	if (in_syscall(regs)) {		continue_addr = regs->pc;		restart_addr = continue_addr - (compat_thumb_mode(regs) ? 2 : 4);		retval = regs->regs[0];		/*		 * Avoid additional syscall restarting via ret_to_user.		 */#暂时忘掉系统调用		forget_syscall(regs);		/*		 * Prepare for system call restart. We do this here so that a		 * debugger will see the already changed PC.		 */		switch (retval) {		case -ERESTARTNOHAND:		case -ERESTARTSYS:		case -ERESTARTNOINTR:		case -ERESTART_RESTARTBLOCK:			regs->regs[0] = regs->orig_x0;			regs->pc = restart_addr;			break;		}	}	/*	 * Get the signal to deliver. When running under ptrace, at this point	 * the debugger may change all of our registers.	 */	if (get_signal(&ksig)) {		/*		 * Depending on the signal settings, we may need to revert the		 * decision to restart the system call, but skip this if a		 * debugger has chosen to restart at a different PC.		 */		if (regs->pc == restart_addr &&		    (retval == -ERESTARTNOHAND ||		     retval == -ERESTART_RESTARTBLOCK ||		     (retval == -ERESTARTSYS &&		      !(ksig.ka.sa.sa_flags & SA_RESTART)))) {			regs->regs[0] = -EINTR;			regs->pc = continue_addr;		}#处理信号量		handle_signal(&ksig, regs);		return;	}	/*	 * Handle restarting a different system call. As above, if a debugger	 * has chosen to restart at a different PC, ignore the restart.	 */#回复系统调用	if (in_syscall(regs) && regs->pc == restart_addr) {		if (retval == -ERESTART_RESTARTBLOCK)			setup_restart_syscall(regs);		user_rewind_single_step(current);	}	restore_saved_sigmask();}

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