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 BB4DAC388F9 for ; Thu, 22 Oct 2020 16:20:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5855E208B6 for ; Thu, 22 Oct 2020 16:20:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603383656; bh=zLqPCnk51tZOSJUktaRPPsIPSiTVlLOBrvuROFwALEM=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=dXMWa4xerw8yDga4oLJxCljC/1c0yZmfbyATTwsPh3DMLVqAJ9DZ2lo1XdCQ11Xc9 ExNFL8M8nQCeScQm5qCO/pGWiVsJT+axortqfalvFzVR9aVbviBzCV0LX0amqyPeaS ve2lR2yG6ICWYLnjveoBo0cLMZcwXDZwZiRufMCI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2901631AbgJVQUz (ORCPT ); Thu, 22 Oct 2020 12:20:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:37298 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2896713AbgJVQUy (ORCPT ); Thu, 22 Oct 2020 12:20:54 -0400 Received: from mail-oi1-f172.google.com (mail-oi1-f172.google.com [209.85.167.172]) (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 B4F2524656 for ; Thu, 22 Oct 2020 16:20:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603383653; bh=zLqPCnk51tZOSJUktaRPPsIPSiTVlLOBrvuROFwALEM=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=PpacB0q4l3++xJYxlDqYZ0g7N6Rp3n2/Td6NUXgQwAqKPW51LSJTIuVYtrPfbhMPm tTelzlU+QrDXyGoHVNnvAoiKoA0CUajmk7kk03Rf75riK0k5Hz05vqwhT4scyMS7ze aElTp4H0yhR+PjLyPw4fLHtNqoAnorNxXIs9NCT0= Received: by mail-oi1-f172.google.com with SMTP id u127so2321533oib.6 for ; Thu, 22 Oct 2020 09:20:53 -0700 (PDT) X-Gm-Message-State: AOAM5304QJ28dxIlpmYR1HQvldA69GqsYiif1wPaBReX3kCpMOLVy1VV qGbPEeRTNoM5FvHfOnLhPifO5P3UkdFGELkuTmM= X-Google-Smtp-Source: ABdhPJyJKWzQKMkBe++rhloUaXwWaemfXfUZLhD4OjX76YJPM98Y/eZmOvVODdnxLvscLE2BWGxbYOJqW6dDwbk49Gw= X-Received: by 2002:aca:4085:: with SMTP id n127mr2135345oia.33.1603383652814; Thu, 22 Oct 2020 09:20:52 -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> In-Reply-To: <20201022161118.GP1551@shell.armlinux.org.uk> From: Ard Biesheuvel Date: Thu, 22 Oct 2020 18:20:40 +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 18:11, 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 =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook wro= te: > > > >> > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > >>> 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 wrote: > > > >>>>> The vfp_kmode_exception() function now is unreachable using rel= ative > > > >>>>> branching in THUMB2 kernel configuration, resulting in a "reloc= ation > > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_ex= ception'" > > > >>>>> 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 sec= tions") ? > > > >>>> That commit may have implicitly moved the location of .vfp11_ven= eer, > > > >>>> 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 F= P exceptions > > > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mo= de > > > >>>>> 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_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=3D90= 18/1 > > > > > > > > > > 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. R_ARM_THM_JUMP19 only has -/+ 1 MB range, i.e., smaller than the size of .text, and so using it for calls to external symbols is still going to be risky, unless we create a completely separate code section for VFP related routines. So we may need the IT instruction anyway, at which point we don't need anything more.