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=-15.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 AB839C433EF for ; Mon, 13 Sep 2021 11:09:32 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1BF4F60FE6 for ; Mon, 13 Sep 2021 11:09:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 1BF4F60FE6 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:60898 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mPjq7-0000qe-At for qemu-devel@archiver.kernel.org; Mon, 13 Sep 2021 07:09:31 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59848) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mPjoJ-0007Fx-3C for qemu-devel@nongnu.org; Mon, 13 Sep 2021 07:07:39 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:49141) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mPjoF-0004ZU-E1 for qemu-devel@nongnu.org; Mon, 13 Sep 2021 07:07:38 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631531252; 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=p8h75J7lg41KqCpWj5qoGkGrzSFdQPM0puDLfsmsMss=; b=Cc8iX+//jVZs7BIqqAylKSJLDv1bDNWShvwq0zogub2k4hy4loqxDNPfyH376W7ardcuuB nAHt/5IYKus+f9sSJV8VOZytLXDIChbH5UyUjNJZbClUD8BRwIB/CioIWNIk5R2iiQDPJj YWcRIpUC93f0U8vDUpMR8/xH3P8F2Xw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-547--OHxJmaFPCK2vce5JdzLoA-1; Mon, 13 Sep 2021 07:07:29 -0400 X-MC-Unique: -OHxJmaFPCK2vce5JdzLoA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CEAE018D6A2C; Mon, 13 Sep 2021 11:07:28 +0000 (UTC) Received: from localhost (unknown [10.39.192.185]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5D1C519E7E; Mon, 13 Sep 2021 11:07:28 +0000 (UTC) Date: Mon, 13 Sep 2021 12:07:27 +0100 From: "Richard W.M. Jones" To: Richard Henderson Subject: Re: [PATCH] tcg/arm: Reduce vector alignment requirement for NEON Message-ID: <20210913110727.GF26415@redhat.com> References: <20210912174925.200132-1-richard.henderson@linaro.org> MIME-Version: 1.0 In-Reply-To: <20210912174925.200132-1-richard.henderson@linaro.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=rjones@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=rjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.398, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peter.maydell@linaro.org, berrange@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Sun, Sep 12, 2021 at 10:49:25AM -0700, Richard Henderson wrote: > With arm32, the ABI gives us 8-byte alignment for the stack. > While it's possible to realign the stack to provide 16-byte alignment, > it's far easier to simply not encode 16-byte alignment in the > VLD1 and VST1 instructions that we emit. > > Remove the assertion in temp_allocate_frame, limit natural alignment > to the provided stack alignment, and add a comment. > > Reported-by: Richard W.M. Jones > Signed-off-by: Richard Henderson > --- > > I haven't seen the assertion with the various arm kernels that I happen > to have laying about. I have not taken the time to build the combo > from the bug report: > > [ 0.000000] Linux version 5.14.0-60.fc36.armv7hl (mockbuild@buildvm-a32-12.iad2.fedoraproject.org) (gcc (GCC) 11.2.1 20210728 (Red Hat 11.2.1-1), GNU ld version 2.37-9.fc36) #1 SMP Mon Aug 30 14:08:34 UTC 2021 > > I thought about parameterizing this patch further, but I can't think of > another ISA that would be affected. (i686 clumsily changed its abi 20 > years ago to avoid faulting on vector spills; other isas so far have > allowed vectors to be unaligned.) Is it possible this change could have caused a more serious regression? Now when I try to boot the Fedora kernel using TCG on armv7hl I can't even get to the point where it detects virtio-scsi devices. Full log is here (go down to the bottom and work backwards): https://kojipkgs.fedoraproject.org//work/tasks/7337/75597337/build.log This might have been caused by a coincidental change to the kernel. The test environment I have makes it extremely difficult to test this change in isolation. However I do know that the same error does _not_ occur on x86-64 guest/host with this patch applied. Rich. > > r~ > --- > tcg/tcg.c | 8 +++++++- > tcg/arm/tcg-target.c.inc | 13 +++++++++---- > 2 files changed, 16 insertions(+), 5 deletions(-) > > diff --git a/tcg/tcg.c b/tcg/tcg.c > index 4142d42d77..ca5bcc4635 100644 > --- a/tcg/tcg.c > +++ b/tcg/tcg.c > @@ -3060,7 +3060,13 @@ static void temp_allocate_frame(TCGContext *s, TCGTemp *ts) > g_assert_not_reached(); > } > > - assert(align <= TCG_TARGET_STACK_ALIGN); > + /* > + * Assume the stack is sufficiently aligned. > + * This affects e.g. ARM NEON, where we have 8 byte stack alignment > + * and do not require 16 byte vector alignment. This seems slightly > + * easier than fully parameterizing the above switch statement. > + */ > + align = MIN(TCG_TARGET_STACK_ALIGN, align); > off = ROUND_UP(s->current_frame_offset, align); > > /* If we've exhausted the stack frame, restart with a smaller TB. */ > diff --git a/tcg/arm/tcg-target.c.inc b/tcg/arm/tcg-target.c.inc > index e5b4f86841..8515717435 100644 > --- a/tcg/arm/tcg-target.c.inc > +++ b/tcg/arm/tcg-target.c.inc > @@ -2477,8 +2477,13 @@ static void tcg_out_ld(TCGContext *s, TCGType type, TCGReg arg, > tcg_out_vldst(s, INSN_VLD1 | 0x7d0, arg, arg1, arg2); > return; > case TCG_TYPE_V128: > - /* regs 2; size 8; align 16 */ > - tcg_out_vldst(s, INSN_VLD1 | 0xae0, arg, arg1, arg2); > + /* > + * We have only 8-byte alignment for the stack per the ABI. > + * Rather than dynamically re-align the stack, it's easier > + * to simply not request alignment beyond that. So: > + * regs 2; size 8; align 8 > + */ > + tcg_out_vldst(s, INSN_VLD1 | 0xad0, arg, arg1, arg2); > return; > default: > g_assert_not_reached(); > @@ -2497,8 +2502,8 @@ static void tcg_out_st(TCGContext *s, TCGType type, TCGReg arg, > tcg_out_vldst(s, INSN_VST1 | 0x7d0, arg, arg1, arg2); > return; > case TCG_TYPE_V128: > - /* regs 2; size 8; align 16 */ > - tcg_out_vldst(s, INSN_VST1 | 0xae0, arg, arg1, arg2); > + /* See tcg_out_ld re alignment: regs 2; size 8; align 8 */ > + tcg_out_vldst(s, INSN_VST1 | 0xad0, arg, arg1, arg2); > return; > default: > g_assert_not_reached(); > -- > 2.25.1 -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW