Re: [PATCH v4 2/2] selftests/ptrace: add a test case for PTRACE_SET_SYSCALL_INFO syscall skipping

[Dmitry V. Levin]

On Wed, Jul 08, 2026 at 11:06:55AM +0200, Renzo Davoli wrote:
> Check whether PTRACE_SET_SYSCALL_INFO syscall skipping semantics implemented in the
> kernel matches userspace expectations.
[...]
> +		ASSERT_LT(ptrace_stop, 4) {
> +			LOG_KILL_TRACEE("ptrace stop overflow");
> +		}

This assertion is redundant given that ...

> +		const unsigned int expected_nr[] = {
> +			__NR_getpid,
> +			__NR_getpid,
> +			__NR_getpid,
> +			__NR_exit_group
> +		};
> +
> +		ASSERT_LT(ptrace_stop, ARRAY_SIZE(expected_nr)) {
> +			LOG_KILL_TRACEE("ptrace stop overflow");
> +		}

... there is a more reliable assertion here instead.

> +		ASSERT_EQ(info.seccomp.nr, expected_nr[ptrace_stop]) {
> +			LOG_KILL_TRACEE("syscall nr mismatch");
> +		}
> +		switch (ptrace_stop) {
> +			case 0:
> +			case 3:
> +				break;

These two cases don't really do anything, feel free to drop them if you
like, it's a matter of style preferences.


-- 
ldv