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=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 EE092C388F7 for ; Thu, 22 Oct 2020 16:33:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 840D62464B for ; Thu, 22 Oct 2020 16:33:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603384411; bh=MHaf3vSH1xQ9JiKezZ0jiRl4izjGveP6G5BPaU4t7Hw=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=or8ga4R+GD5Kzvkj9O4iD9XLOFQu1Y8T/CLOOzJ56DVnjA0aJ15B0N+1fn74icf88 opZUjShMbGaCFUvfWoLTWEdepmo3L9+PUR3jt/qjXzrurdSUzg9PPoTAJ1X/RCLImx A2AqRDYbuA7Pr50z7tX2Ld4GRQCWnp4Z31gyGTJ4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2901747AbgJVQda (ORCPT ); Thu, 22 Oct 2020 12:33:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:45732 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2897182AbgJVQda (ORCPT ); Thu, 22 Oct 2020 12:33:30 -0400 Received: from mail-oi1-f173.google.com (mail-oi1-f173.google.com [209.85.167.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 45A922464E for ; Thu, 22 Oct 2020 16:33:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603384409; bh=MHaf3vSH1xQ9JiKezZ0jiRl4izjGveP6G5BPaU4t7Hw=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=mdiQveJ6jqA2tn9p9FQc+VbkEkpvOzvXhg8fgtUO2VLysb8l2LDhf4DZh0taTunuU KD6omN4oIPWCXGADuGy4jyCGtMmS7YO8q/rO+T3qoW3Z1wH76gl1rliqMkbCGjpAO8 /WMaWI4Rp0YPCldxVsC/B7e2w8bS3i4YTiOsCf/s= Received: by mail-oi1-f173.google.com with SMTP id s21so2390113oij.0 for ; Thu, 22 Oct 2020 09:33:29 -0700 (PDT) X-Gm-Message-State: AOAM530HbyImQbQz1nC8XCi4h06aoPNtIzFFaZ3txC1Jh7EMNy/bEI8D 7j4pe2UqPbHZv76vROvJiHKPYyCiqyP/fB3tutk= X-Google-Smtp-Source: ABdhPJwFmV6m+1DHYPPCsqQf/Ynk4xtZa0pForOUwyADxVgNPP2lPCVvVFnY3EpetbWGlYZpWKYNvyVpdQeTjSzk76I= X-Received: by 2002:aca:4085:: with SMTP id n127mr2174403oia.33.1603384408423; Thu, 22 Oct 2020 09:33:28 -0700 (PDT) MIME-Version: 1.0 References: <20201021225737.739-1-digetx@gmail.com> <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> In-Reply-To: <20201022162334.GQ1551@shell.armlinux.org.uk> From: Ard Biesheuvel Date: Thu, 22 Oct 2020 18:33:17 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v1] ARM: vfp: Use long jump to fix THUMB2 kernel compilation error To: Russell King - ARM Linux admin Cc: Dmitry Osipenko , Kees Cook , Nick Desaulniers , Linux Kernel Mailing List , clang-built-linux , Ingo Molnar , Linux ARM Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 wr= ote: > > > > > > > > > > 22.10.2020 10:06, Ard Biesheuvel =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > > > > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook = wrote: > > > > > >> > > > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrot= e: > > > > > >>> 22.10.2020 02:40, Kees Cook =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > > > > > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wr= ote: > > > > > >>>>> The vfp_kmode_exception() function now is unreachable using= relative > > > > > >>>>> branching in THUMB2 kernel configuration, resulting in a "r= elocation > > > > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmod= e_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 in= put 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 n= or FP exceptions > > > > > >>>>> and r3, r3, #MODE_MASK @ are supported in kerne= l mode > > > > > >>>>> teq r3, #USR_MODE > > > > > >>>>> - bne vfp_kmode_exception @ Returns through lr > > > > > >>>>> + ldr r1, =3Dvfp_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_ven= eer 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 v= ery 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= =3D9018/1 > > > > > > > > > > > > > > > > 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 differen= t > > > 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 u= p > > > 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? > Your patch may be a single line, but it has a slightly greater > impact than the alternative two line solution. >