From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 48FE1C32788 for ; Thu, 11 Oct 2018 12:53:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 19AAF20652 for ; Thu, 11 Oct 2018 12:53:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 19AAF20652 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728386AbeJKUUL (ORCPT ); Thu, 11 Oct 2018 16:20:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36350 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726135AbeJKUUL (ORCPT ); Thu, 11 Oct 2018 16:20:11 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9752F5F724; Thu, 11 Oct 2018 12:53:06 +0000 (UTC) Received: from treble (ovpn-122-227.rdu2.redhat.com [10.10.122.227]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7F8BF7A536; Thu, 11 Oct 2018 12:53:01 +0000 (UTC) Date: Thu, 11 Oct 2018 07:52:58 -0500 From: Josh Poimboeuf To: Andy Lutomirski Cc: Steven Rostedt , Peter Zijlstra , LKML , Linus Torvalds , Ingo Molnar , Andrew Morton , Thomas Gleixner , Masami Hiramatsu , Mathieu Desnoyers , Matthew Helsley , "Rafael J. Wysocki" , David Woodhouse , Paolo Bonzini , Jason Baron , Jiri Kosina , Ard Biesheuvel , Andrew Lutomirski Subject: Re: [POC][RFC][PATCH 1/2] jump_function: Addition of new feature "jump_function" Message-ID: <20181011125258.ihsdmonepaoc5xtb@treble> References: <20181008155757.GC5663@hirez.programming.kicks-ass.net> <20181009021710.qwt5hpntyeps44h3@treble> <20181008235750.59da83ae@gandalf.local.home> <20181010175237.e7m3sldcu2maoqcq@treble> <20181010181605.arsyjxwdztztrjih@treble> <20181010181741.lc4l7kjvcmoxrw5b@treble> <20181011030738.wwy6grnss67txd2l@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181011030738.wwy6grnss67txd2l@treble> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 11 Oct 2018 12:53:07 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 10, 2018 at 10:07:38PM -0500, Josh Poimboeuf wrote: > On Wed, Oct 10, 2018 at 02:13:22PM -0700, Andy Lutomirski wrote: > > On Wed, Oct 10, 2018 at 11:17 AM Josh Poimboeuf wrote: > > > > > > On Wed, Oct 10, 2018 at 01:16:05PM -0500, Josh Poimboeuf wrote: > > > > On Wed, Oct 10, 2018 at 11:03:43AM -0700, Andy Lutomirski wrote: > > > > > > +#define DECLARE_STATIC_CALL(tramp, func) \ > > > > > > + extern typeof(func) tramp; \ > > > > > > + static void __used __section(.discard.static_call_tramps) \ > > > > > > + *__static_call_tramp_##tramp = tramp > > > > > > + > > > > > > > > > > Confused. What's the __static_call_tramp_##tramp variable for? And > > > > > why is a DECLARE_ macro defining a variable? > > > > > > > > This is the magic needed for objtool to find all the call sites. > > > > > > > > The variable itself isn't needed, but the .discard.static_call_tramps > > > > entry is. Objtool reads that section to find out which function call > > > > sites are targeted to a static call trampoline. > > > > > > To clarify: objtool reads that section to find out which functions are > > > really static call trampolines. Then it annotates all the instructions > > > which call/jmp to those trampolines. Those annotations are then read by > > > the kernel. > > > > > > > Ah, right, and objtool runs on a per-object basis so it has no other > > way to know what symbols are actually static calls. > > > > There's another way to skin this cat, though: > > > > extern typeof(func) __static_call_trampoline_##tramp; > > #define tramp __static_call_trampoline_##tramp > > > > And objtool could recognize it by name. But, of course, you can't put > > a #define in a macro. But maybe there's a way to hack it up with a > > static inline? I went with something similar in the latest version. It's less surprising in a couple of ways: - DECLARE_STATIC_CALL doesn't have the magic objtool definition. - Call sites use the static_call() wrapper, which makes static calls clearly visible. #define STATIC_CALL_TRAMP(key) ____static_call_tramp_##key #define STATIC_CALL_PTR(key) ____static_call_ptr_##key #define STATIC_CALL_TRAMP_STR(key) __stringify(STATIC_CALL_TRAMP(key)) #define STATIC_CALL_PTR_STR(key) __stringify(STATIC_CALL_PTR(key)) #define DECLARE_STATIC_CALL(key, func) \ extern typeof(func) STATIC_CALL_TRAMP(key); \ extern typeof(func) *STATIC_CALL_PTR(key) #define DEFINE_STATIC_CALL(key, func) \ typeof(func) *STATIC_CALL_PTR(key) = func; \ asm(".pushsection .text, \"ax\" \n" \ ".align 4 \n" \ ".globl " STATIC_CALL_TRAMP_STR(key) " \n" \ ".type " STATIC_CALL_TRAMP_STR(key) ", @function \n" \ STATIC_CALL_TRAMP_STR(key) ": \n" \ "jmpq *" STATIC_CALL_PTR_STR(key) "(%rip) \n" \ ".popsection \n") #define static_call(key, args...) STATIC_CALL_TRAMP(key)(args) #define static_call_update(key, func) \ ({ \ STATIC_CALL_PTR(key) = func; \ __static_call_update((void **)&STATIC_CALL_PTR(key)); \ }) -- Josh