From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 346B83858000 for ; Thu, 9 Dec 2021 07:42:46 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 346B83858000 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-19-hzHYR4I4PAaLDBEAueu0sA-1; Thu, 09 Dec 2021 02:42:42 -0500 X-MC-Unique: hzHYR4I4PAaLDBEAueu0sA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7A6DF835E44; Thu, 9 Dec 2021 07:42:41 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.193.123]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 87A4419D9B; Thu, 9 Dec 2021 07:42:40 +0000 (UTC) From: Florian Weimer To: Siddhesh Poyarekar Cc: libc-alpha@sourceware.org Subject: Re: [PATCH 4/8] nptl: Add rseq registration References: <921551c8-0cd3-5fcc-30a4-e0709485e0f1@gotplt.org> <87ilvzj7ev.fsf@oldenburg.str.redhat.com> Date: Thu, 09 Dec 2021 08:42:38 +0100 In-Reply-To: (Siddhesh Poyarekar's message of "Thu, 9 Dec 2021 04:57:15 +0530") Message-ID: <87a6hai5qp.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-6.5 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 09 Dec 2021 07:42:47 -0000 * Siddhesh Poyarekar: > On 12/8/21 23:38, Florian Weimer wrote: >> * Siddhesh Poyarekar: >> >>>> +#ifdef RSEQ_SIG >>>> +static inline void >>>> +rseq_register_current_thread (struct pthread *self) >>>> +{ >>>> + int ret = INTERNAL_SYSCALL_CALL (rseq, >>>> + &self->rseq_area, sizeof (self->rseq_area), >>>> + 0, RSEQ_SIG); >>>> + if (INTERNAL_SYSCALL_ERROR_P (ret)) >>>> + THREAD_SETMEM (self, rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED); >>> >>> Why can't we just leave it as the kernel did when it failed the >>> syscall? >> The kernel definitely won't write anything if the failure is ENOSYS. >> I >> don't expect the kernel to write something for the other failures, >> either. > > OK, I interpreted the from the outdated manpage patch[1] that the > kernel ensures that uninitialized cpu_id will be read as -1. I read > the rseq implementation in the kernel and saw that there are a number > of error paths where the kernel simply returns without touching the > user memory. I suppose what they meant by "uninitialized" in the > manpage is actually "reset after unregister", which is odd. > > In any case, what I meant to eventually get at (sorry I wasn't > specific; I wrote both patch reviews together and didn't realize > they'd be read as separate emails!) is that RSEQ_CPU_ID_UNINITIALIZED > seemed enough for all use cases and RSEQ_CPU_ID_REGISTRATION_FAILED > seemed unnecessary. Yes, but the constant is (also) defined in the UAPI headers, so it's value is fixed. And RSEQ_CPU_ID_REGISTRATION_FAILED (that is, -2) is closer to the behavior we want to trigger in application (that there is nothing to register because we already tried and failed). Thanks, Florian