Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752705AbaKGNLj (ORCPT ); Fri, 7 Nov 2014 08:11:39 -0500 Received: from foss-mx-na.foss.arm.com ([217.140.108.86]:54539 "EHLO foss-mx-na.foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752130AbaKGNLh (ORCPT ); Fri, 7 Nov 2014 08:11:37 -0500 Date: Fri, 7 Nov 2014 13:11:30 +0000 From: Will Deacon To: Arnd Bergmann Cc: "linux-arm-kernel@lists.infradead.org" , Russell King - ARM Linux , "linaro-kernel@lists.linaro.org" , "keescook@chromium.org" , "roland@hack.frob.com" , "oleg@redhat.com" , "linux-kernel@vger.kernel.org" , AKASHI Takahiro , "dsaxena@linaro.org" Subject: Re: [RFC] ptrace: add generic SET_SYSCALL request Message-ID: <20141107131129.GF18916@arm.com> References: <1415346443-28915-1-git-send-email-takahiro.akashi@linaro.org> <1678531.AUssrM9PAs@wuerfel> <20141107121119.GQ4042@n2100.arm.linux.org.uk> <353850534.aGkkrtTogX@wuerfel> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <353850534.aGkkrtTogX@wuerfel> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 07, 2014 at 12:44:07PM +0000, Arnd Bergmann wrote: > On Friday 07 November 2014 12:11:19 Russell King - ARM Linux wrote: > > On Fri, Nov 07, 2014 at 01:03:00PM +0100, Arnd Bergmann wrote: > > > On Friday 07 November 2014 11:55:51 Will Deacon wrote: > > > > We need this for arm64 and, since all architectures seem to have a mechanism > > > > for setting a system call via ptrace, moving it to generic code should make > > > > sense for new architectures too, no? > > > > > > It makes a little more sense now, but I still don't understand why you > > > need to set the system call number via ptrace. What is this used for, > > > and why doesn't any other architecture have this? > > > > All other architectures have a way. x86, for example, you set orig_eax > > (or orig_rax) to change the syscall number. On ARM, that doesn't work > > because we don't always pass the syscall number in a register. > > > > Sorry for being slow today, but why can't we use the same interface that > s390 has on arm64: > > static int s390_system_call_get(struct task_struct *target, > const struct user_regset *regset, > unsigned int pos, unsigned int count, > void *kbuf, void __user *ubuf) > { > unsigned int *data = &task_thread_info(target)->system_call; > return user_regset_copyout(&pos, &count, &kbuf, &ubuf, > data, 0, sizeof(unsigned int)); > } > > static int s390_system_call_set(struct task_struct *target, > const struct user_regset *regset, > unsigned int pos, unsigned int count, > const void *kbuf, const void __user *ubuf) > { > unsigned int *data = &task_thread_info(target)->system_call; > return user_regset_copyin(&pos, &count, &kbuf, &ubuf, > data, 0, sizeof(unsigned int)); > } > > static const struct user_regset s390_regsets[] = { > ... > { > .core_note_type = NT_S390_SYSTEM_CALL, > .n = 1, > .size = sizeof(unsigned int), > .align = sizeof(unsigned int), > .get = s390_system_call_get, > .set = s390_system_call_set, > }, > ... > }; > > Is it just preference for being consistent with ARM32, or is there a > reason this won't work? Interesting, I hadn't considered a unit-length regset. > It's not that I care strongly about the interface, my main point is > that the changelog doesn't describe why one interface was used instead > the other. I suspect the current approach was taken because it follows the same scheme as 32-bit ARM. If both methods are sufficient (Kees would have a better idea than me on that), then I don't have a strong preference. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/