Re: [RFC][ATCH 1/3] ptrace: Remove maxargs from task_current_syscall()

[Steven Rostedt]

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

> On Tue, Nov 8, 2016 at 8:16 AM, Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxx> 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