linux-kernel - Re: [PATCH v4 2/2] ptrace: add PTRACE_GET_SYSCALL

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Date:   Wed, 28 Nov 2018 15:10:50 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Dmitry V. Levin" <ldv@...linux.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Elvira Khabirova <lineprinter@...linux.org>,
        Eugene Syromyatnikov <esyr@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        strace-devel@...ts.strace.io
Subject: Re: [PATCH v4 2/2] ptrace: add PTRACE_GET_SYSCALL_INFO request

On 11/28, Dmitry V. Levin wrote:
>
> +static unsigned long
> +ptrace_get_syscall_info_entry(struct task_struct *child,
> +			      struct ptrace_syscall_info *info)
> +{
> +	struct pt_regs *regs = task_pt_regs(child);
> +	unsigned long args[ARRAY_SIZE(info->entry.args)];
> +	int i;
> +
> +	info->op = PTRACE_SYSCALL_INFO_ENTRY;
> +	info->arch = syscall_get_arch(child);
> +	info->entry.nr = syscall_get_nr(child, regs);
> +	info->entry.instruction_pointer = instruction_pointer(regs);
> +	info->entry.stack_pointer = user_stack_pointer(regs);
> +	info->entry.frame_pointer = frame_pointer(regs);
> +	syscall_get_arguments(child, regs, 0, ARRAY_SIZE(args), args);
> +	for (i = 0; i < ARRAY_SIZE(args); i++)
> +		info->entry.args[i] = args[i];

I must have missed something, but why do we need the temporary args[],
syscall_get_arguments(..., info->entry.args) should equally work?

Oleg.