Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932758AbcKHQVO (ORCPT ); Tue, 8 Nov 2016 11:21:14 -0500 Received: from mail-vk0-f43.google.com ([209.85.213.43]:33655 "EHLO mail-vk0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751099AbcKHQVK (ORCPT ); Tue, 8 Nov 2016 11:21:10 -0500 MIME-Version: 1.0 In-Reply-To: References: <20161107212634.529267342@goodmis.org> <20161107213233.466776454@goodmis.org> From: Andy Lutomirski Date: Tue, 8 Nov 2016 08:20:48 -0800 Message-ID: Subject: Re: [RFC][ATCH 1/3] ptrace: Remove maxargs from task_current_syscall() To: Linus Torvalds Cc: Steven Rostedt , Linux Kernel Mailing List , Ingo Molnar , Andrew Morton , Roland McGrath , Oleg Nesterov , "linux-arch@vger.kernel.org" , Peter Zijlstra Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1948 Lines: 45 On Tue, Nov 8, 2016 at 8:16 AM, Linus Torvalds 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 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'. > > For example, kernel/seccomp.c does this instead: > > sd->nr = syscall_get_nr(task, regs); > sd->arch = syscall_get_arch(); > syscall_get_arguments(task, regs, 0, 6, args); > sd->args[0] = args[0]; > sd->args[1] = args[1]; > sd->args[2] = args[2]; > sd->args[3] = args[3]; > sd->args[4] = args[4]; > sd->args[5] = args[5]; > sd->instruction_pointer = KSTK_EIP(task); It's a bit hard to tell from seccomp.c, but x86 carefully arranges for that code to never get run -- instead the entry code supplies a struct seccomp_data. Other arches could follow suit for a nice speedup. --Andy