Re: [RFC] PATCH 3/4 - Time virtualization : PTRACE_SYSCALL_MASK

[Heiko Carstens <heiko.carstens@de.ibm.com>]

> Add PTRACE_SYSCALL_MASK, which allows system calls to be selectively
> traced.  It takes a bitmask and a length.  A system call is traced
> if its bit is one.  Otherwise, it executes normally, and is
> invisible to the ptracing parent.
> [...]
> +int set_syscall_mask(struct task_struct *child, char __user *mask,
> +		     unsigned long len)
> +{
> +	int i, n = (NR_syscalls + 7) / 8;
> +	char c;
> +
> +	if(len > n){
> +		for(i = NR_syscalls; i < len * 8; i++){
> +			get_user(c, &mask[i / 8]);
> +			if(!(c & (1 << (i % 8)))){
> +				printk("Out of range syscall at %d\n", i);
> +				return -EINVAL;
> +			}
> +		}
> +
> +		len = n;
> +	}

Since it's quite likely that len > n will be true (e.g. after installing the
latest version of your debug tool) it would be better to silently ignore all
bits not within the range of NR_syscalls.
There is no point in flooding the console. The tracing process won't see any
of the non existant syscalls it requested to see anyway.