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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CF68CC433F5 for ; Fri, 5 Nov 2021 18:02:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A49EE60F56 for ; Fri, 5 Nov 2021 18:02:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234521AbhKESFC (ORCPT ); Fri, 5 Nov 2021 14:05:02 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:37747 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231689AbhKESFA (ORCPT ); Fri, 5 Nov 2021 14:05:00 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1636135340; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=YAIOATAtg7S/5QdcjsIeXtk0TxOFUbQvA2ViOYkKT0k=; b=OjKc+wCGOFpw3hamqf7BMwzX2td2952ssu6FRKuwCJYL+D4Tyv7ECsPeR8OBb/7jHn0XrM pg0g0Kvo187iO5/7GjgsnU0/cVG/jl3kEtpD8W4befbkj4Q4aeekAbVuWD4GA/CVVw0/ft YLikUqrkroipcWIeONenMYEWcP5UfF4= Received: from mail-qk1-f200.google.com (mail-qk1-f200.google.com [209.85.222.200]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-34-rHnaNGS2OcirRhPJL-vljA-1; Fri, 05 Nov 2021 14:02:19 -0400 X-MC-Unique: rHnaNGS2OcirRhPJL-vljA-1 Received: by mail-qk1-f200.google.com with SMTP id h2-20020a05620a10a200b00462c87635cdso7660374qkk.15 for ; Fri, 05 Nov 2021 11:02:19 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=YAIOATAtg7S/5QdcjsIeXtk0TxOFUbQvA2ViOYkKT0k=; b=5f48jE/jjVGDPmlqQX8pS/hgtULz1xwsU7fAK0pAetk+BotUT8Iuf+MZF+2z/zTEnw SZHxpDipi3+tsZNUNCnEKqxXABGjDpEDT5vk3KKzvkcRThA5a2t8yyek9dCePa+CnV2y JUAREA+P97iEeVpbCz+IdyLFwvHA+qY+SEmv8Ad+yoitclHSldvyadgm7Zl6c9xG/mXG q75ecLjg4wr7/ETSawKbTE5H2TuzyhH9H2397WERVp0edmoz3Y1F4UEqNVlxHPz7P7j1 8G8UGJUTsw9yIzOCN0TmKpVWsbk0g+u1HdhE1iXjuVM3ZzylgZUl+MJaBV8kk4cFu6zI sKow== X-Gm-Message-State: AOAM530IBPD5zqgm7e9yeNwvclWJhp7/wyC0V8m66hNXmagGHQK8QLYO 7T28DvhTUBRyvGp90rnULZTFXPThkvtAZ8BBplEnN+c0NceUwxx5acGBEQnN2YrUMBE2NI19+Z7 f0nnbs+P5sNgivJEsfBz9gDFW X-Received: by 2002:ad4:5c6c:: with SMTP id i12mr32753041qvh.42.1636135338795; Fri, 05 Nov 2021 11:02:18 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwoJlrWeeXAA9E4RVT0sdHxUWx5aU/GxeHJMPr563FntFFktlUcFjKjmgn+CK19161PSGLP3g== X-Received: by 2002:ad4:5c6c:: with SMTP id i12mr32753016qvh.42.1636135338575; Fri, 05 Nov 2021 11:02:18 -0700 (PDT) Received: from treble ([2600:1700:6e32:6c00::a]) by smtp.gmail.com with ESMTPSA id j13sm6061456qkp.111.2021.11.05.11.02.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Nov 2021 11:02:18 -0700 (PDT) Date: Fri, 5 Nov 2021 11:01:52 -0700 From: Josh Poimboeuf To: Peter Zijlstra Cc: x86@kernel.org, linux-kernel@vger.kernel.org, mark.rutland@arm.com, dvyukov@google.com, seanjc@google.com, pbonzini@redhat.com, mbenes@suse.cz Subject: Re: [PATCH 20/22] x86,word-at-a-time: Remove .fixup usage Message-ID: <20211105180152.oi7h3p6fb6c5pjkf@treble> References: <20211105171023.989862879@infradead.org> <20211105171821.654356149@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20211105171821.654356149@infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 05, 2021 at 06:10:43PM +0100, Peter Zijlstra wrote: > +#ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT > + > +static inline unsigned long load_unaligned_zeropad(const void *addr) > +{ > + unsigned long offset, data; > + unsigned long ret; > + > + asm_volatile_goto( > + "1: mov %[mem], %[ret]\n" > + > + _ASM_EXTABLE(1b, %l[do_exception]) > + > + : [ret] "=&r" (ret) > + : [mem] "m" (*(unsigned long *)addr) > + : : do_exception); > + > +out: > + return ret; > + > +do_exception: __cold; > + > + offset = (unsigned long)addr & (sizeof(long) - 1); > + addr = (void *)((unsigned long)addr & ~(sizeof(long) - 1)); > + data = *(unsigned long *)addr; > + ret = data >> offset * 8; > + goto out; Superfluous goto, can just return here? > static inline unsigned long load_unaligned_zeropad(const void *addr) > { > - unsigned long ret, dummy; > + unsigned long offset, data; > + unsigned long ret, err = 0; > > - asm( > - "1:\tmov %2,%0\n" > + asm( "1: mov %[mem], %[ret]\n" > "2:\n" > - ".section .fixup,\"ax\"\n" > - "3:\t" > - "lea %2,%1\n\t" > - "and %3,%1\n\t" > - "mov (%1),%0\n\t" > - "leal %2,%%ecx\n\t" > - "andl %4,%%ecx\n\t" > - "shll $3,%%ecx\n\t" > - "shr %%cl,%0\n\t" > - "jmp 2b\n" > - ".previous\n" > - _ASM_EXTABLE(1b, 3b) > - :"=&r" (ret),"=&c" (dummy) > - :"m" (*(unsigned long *)addr), > - "i" (-sizeof(unsigned long)), > - "i" (sizeof(unsigned long)-1)); > + > + _ASM_EXTABLE_FAULT(1b, 2b) > + > + : [ret] "=&r" (ret), "+a" (err) > + : [mem] "m" (*(unsigned long *)addr)); > + > + if (unlikely(err)) { > + offset = (unsigned long)addr & (sizeof(long) - 1); > + addr = (void *)((unsigned long)addr & ~(sizeof(long) - 1)); > + data = *(unsigned long *)addr; > + ret = data >> offset * 8; > + } > + > return ret; This adds a (normally not taken) conditional jump, would a straight jmp over the fixup not be better? i.e. 1: mov %[mem], %[ret] jmp 2 ... fixup code ... 2: -- Josh