linux-kernel - Re: [RFC][ATCH 1/3] ptrace: Remove maxargs from task_current

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Message-ID: <20161108144851.7a35c37d@gandalf.local.home>
Date:   Tue, 8 Nov 2016 14:48:51 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roland McGrath <roland@...k.frob.com>,
        Oleg Nesterov <oleg@...hat.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC][ATCH 1/3] ptrace: Remove maxargs from
 task_current_syscall()

On Tue, 8 Nov 2016 08:20:48 -0800
Andy Lutomirski <luto@...capital.net> wrote:

> On Tue, Nov 8, 2016 at 8:16 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> > So I definitely approve of the change, but I wonder if we should go
> > one step further:
> >
> > On Mon, Nov 7, 2016 at 1:26 PM, Steven Rostedt <rostedt@...dmis.org> wrote:  
> >>
> >>  extern int task_current_syscall(struct task_struct *target, long *callno,
> >> -                               unsigned long args[6], unsigned int maxargs,
> >> -                               unsigned long *sp, unsigned long *pc);
> >> +                               unsigned long args[6], unsigned long *sp,
> >> +                               unsigned long *pc);  
> >
> > The thing is, in C, having an array in a function declaration is
> > pretty much exactly the same as just having a pointer, so from a type
> > checking standpoint it doesn't really help all that much (but from a
> > "human documentation" side the "args[6]" is much better than "*args").
> >
> > However, what would really help type checking is making it a
> > structure. And maybe that structure could just contain "callno", "sp"
> > and "pc" too? That would not only fix the type checking, it would make
> > the calling convention even cleaner. Just have one single structure
> > that contains all the relevant data.  
> 
> I would propose calling this 'struct seccomp_data'.

I'm assuming you mean to use the existing seccomp_data? But isn't that
already defined as a user structure? Thus, we can't add sp and pc to it.

I can change syscall_get_arguments() to take the seccomp_data as an
input, and just fill in the arguments directly.

-- Steve