Re: [PATCH 2/6] riscv/ftrace: Add dynamic function tracer support

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 10 Jan 2018 15:38:10 +0800
Alan Kao <nonerkao@gmail.com> wrote:

> +static int ftrace_check_current_call(unsigned long hook_pos,
> +				     unsigned int *expected)
> +{
> +	unsigned int replaced[2];
> +	unsigned int nops[2] = {NOP4, NOP4};
> +
> +	/* we expect nops at the hook position */
> +	if (!expected)
> +		expected = nops;
> +
> +	/* read the text we want to modify */
> +	if (probe_kernel_read(replaced, (void *)hook_pos, MCOUNT_INSN_SIZE))
> +		return -EFAULT;
> +
> +	/* Make sure it is what we expect it to be */
> +	if (replaced[0] != expected[0] || replaced[1] != expected[1]) {

I wonder if we can have a slight enhancement by doing:

	if (memcmp(replaced, expected, sizeof(replaced)) != 0) {

-- Steve


> +		pr_err("%p: expected (%08x %08x) but get (%08x %08x)",
> +		       (void *)hook_pos, expected[0], expected[1], replaced[0],
> +		       replaced[1]);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}