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=-8.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 ECE26C4363A for ; Thu, 22 Oct 2020 17:48:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6FA0F206DD for ; Thu, 22 Oct 2020 17:48:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="Uhc6UUVl" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S369377AbgJVRsa (ORCPT ); Thu, 22 Oct 2020 13:48:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36134 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2901073AbgJVRsa (ORCPT ); Thu, 22 Oct 2020 13:48:30 -0400 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:32c8:5054:ff:fe00:142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E0E50C0613CE for ; Thu, 22 Oct 2020 10:48:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=1ZcxKmveMq3q1xnEh7xaia3hz4ZSwMr6bcgK6ANNCh0=; b=Uhc6UUVlsvGCIF6md6Oy9gxtU LXAbXFf3a4ZIzhz8F0HMuWtlqJk11URGNI9Ni8s5UiZJStocRX6gfPJ7DblVg5kjMpMlpqZmkgl// iomldTUmfRCwgLXAfJbdjCNq2AgqcqrREDXiVcL3AsVag7wQCQLfnoyicEo1VQqj+jVWgsWEepaF9 DXVrkx6+lc0bErGPii0wGIaIRTcTu7NDJjhvUknmBzsqlhfa0snM05l5Z80bOdLQqTJwgUDHIxGUQ Hm9EMMYgLm1H4mIx6XG29ea/UFH5UX+GX/0IXbU+U3SVh+J6eZRcDm6wLC3S6kjV2Y66EZELayeBy jebPFhcQw==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:49604) by pandora.armlinux.org.uk with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1kVehP-0002Na-6m; Thu, 22 Oct 2020 18:48:27 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1kVehO-0007bE-Hr; Thu, 22 Oct 2020 18:48:26 +0100 Date: Thu, 22 Oct 2020 18:48:26 +0100 From: Russell King - ARM Linux admin To: Ard Biesheuvel Cc: Dmitry Osipenko , Kees Cook , Nick Desaulniers , Linux Kernel Mailing List , clang-built-linux , Ingo Molnar , Linux ARM Subject: Re: [PATCH v1] ARM: vfp: Use long jump to fix THUMB2 kernel compilation error Message-ID: <20201022174826.GS1551@shell.armlinux.org.uk> References: <202010211637.7CFD8435@keescook> <773fbdb0-5fc4-ab39-e72d-89845faa4c6d@gmail.com> <202010212028.32E8A5EF9B@keescook> <1d2e2b5d-3035-238c-d2ca-14c0c209a6a1@gmail.com> <20201022161118.GP1551@shell.armlinux.org.uk> <20201022162334.GQ1551@shell.armlinux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: Russell King - ARM Linux admin Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 22, 2020 at 06:33:17PM +0200, Ard Biesheuvel wrote: > On Thu, 22 Oct 2020 at 18:23, Russell King - ARM Linux admin > wrote: > > > > On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: > > > On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin > > > wrote: > > > > > > > > On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > > > > On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko wrote: > > > > > > > > > > > > 22.10.2020 10:06, Ard Biesheuvel пишет: > > > > > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook wrote: > > > > > > >> > > > > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > > > > >>> 22.10.2020 02:40, Kees Cook пишет: > > > > > > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > > > > > >>>>> The vfp_kmode_exception() function now is unreachable using relative > > > > > > >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > > > > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > > > > > >>>>> linker error. Let's use long jump in order to fix the issue. > > > > > > >>>> > > > > > > >>>> Eek. Is this with gcc or clang? > > > > > > >>> > > > > > > >>> GCC 9.3.0 > > > > > > >>> > > > > > > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > > > > >>>> > > > > > > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > > > > > >>>> That commit may have implicitly moved the location of .vfp11_veneer, > > > > > > >>>> though I thought I had chosen the correct position. > > > > > > >>> > > > > > > >>> I re-checked that the fixes tag is correct. > > > > > > >>> > > > > > > >>>>> Signed-off-by: Dmitry Osipenko > > > > > > >>>>> --- > > > > > > >>>>> arch/arm/vfp/vfphw.S | 3 ++- > > > > > > >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > >>>>> > > > > > > >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > > > > > >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > > > > > >>>>> --- a/arch/arm/vfp/vfphw.S > > > > > > >>>>> +++ b/arch/arm/vfp/vfphw.S > > > > > > >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > > > > > >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > > > > > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > > > > > >>>>> teq r3, #USR_MODE > > > > > > >>>>> - bne vfp_kmode_exception @ Returns through lr > > > > > > >>>>> + ldr r1, =vfp_kmode_exception > > > > > > >>>>> + bxne r1 @ Returns through lr > > > > > > >>>>> > > > > > > >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > > > > > >>>>> DBGSTR1 "fpexc %08x", r1 > > > > > > >>>> > > > > > > >>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > > > > > >>>> moving? > > > > > > >>>> > > > > > > >>> > > > > > > >>> I don't know where it needs to be moved. Please feel free to make a > > > > > > >>> patch if you have a better idea, I'll be glad to test it. > > > > > > >> > > > > > > >> I might have just been distracted by the common "vfp" prefix. It's > > > > > > >> possible that the text section shuffling just ended up being very large, > > > > > > >> so probably this patch is right then! > > > > > > >> > > > > > > > > > > > > > > I already sent a fix for this issue: > > > > > > > > > > > > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > > > > > > > > > > > > > > > > The offending commit contains stable tag, so I assume that fixes tag is > > > > > > mandatory. Yours patch misses the fixes tag. > > > > > > > > > > Russell, mind adding that? Or would you like me to update the patch in > > > > > the patch system? > > > > > > > > Rather than adding the IT, I'm suggesting that we solve it a different > > > > way - ensuring that the two bits of code are co-located. There's no > > > > reason for them to be separated, and the assembly code entry point is > > > > already called indirectly. > > > > > > > > The problem is the assembly ends up in the .text section which ends up > > > > at the start of the binary, but depending on the compiler, functions > > > > in .c files end up in their own sections. It would be good if, as > > > > Dmitry has shown that it is indeed possible, to have them co-located. > > > > > > Why is that better? I provided a minimal fix which has zero impact on > > > ARM builds, and minimal impact on Thumb2 builds, given that it retains > > > the exact same semantics as before, but using a different opcode. > > > > I think you just described the reason there. Why should we force > > everything to use a different opcode when a short jump _should_ > > suffice? > > > > Why should a short jump suffice? The call is to vfp_kmode_exception(), > which we only call in exceptional cases. Why would we want to keep > that in close proximity? You're thinking about it in terms of what happens when the branch is taken, rather than also considering that this code path is also traversed for _every_ single time that we enter the support code not just for kernel mode. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!