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 3FA29C2D0A3 for ; Thu, 29 Oct 2020 09:56:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C58392076E for ; Thu, 29 Oct 2020 09:56:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603965397; bh=UIUUMTuyyFka0yoGb4mpTbAWzZnbo3bGVVQRoUp8wo4=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=L/BJkY0KCvK5o7DrSqSg8B1rdf5wdkq4RhMv4BXTARXr2C9bUbjr8mbIP1pAXPCJk pdvvowIbpNaR19qv7oQKn5LeJSepNj2laDwC2J8NCGAjIJBwg+seO1CEhdtvnc00FB LP+bjXx320jUtvUJ1K72uNFJajiV413o6A2z05kg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726763AbgJ2J4g (ORCPT ); Thu, 29 Oct 2020 05:56:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:42052 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725779AbgJ2J4f (ORCPT ); Thu, 29 Oct 2020 05:56:35 -0400 Received: from mail-ot1-f42.google.com (mail-ot1-f42.google.com [209.85.210.42]) (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 4E79E2076D for ; Thu, 29 Oct 2020 09:56:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603965394; bh=UIUUMTuyyFka0yoGb4mpTbAWzZnbo3bGVVQRoUp8wo4=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=OtLUM0aPNA3YlDXPv4hEUQBPXiNMyw1JGQfALl024K4Hs0bBx0IuTDJcZ9A2ambLe N7z2km37pTevSz/a8IL4IfDL5VCv+ffNw5csk0c3TUy6QGXO/iBoFFyjcx+HOpw0NM vPFqJh4/P742+7N7imEO9tZyMRbouaFK3ZCaisTU= Received: by mail-ot1-f42.google.com with SMTP id f97so1738918otb.7 for ; Thu, 29 Oct 2020 02:56:34 -0700 (PDT) X-Gm-Message-State: AOAM5307dS8k68bJEOBfczeXNQ80ZBH2ZZg1muwGMxfTRjO+1B3W0oTV iyl8h2OOrxaLVjp2ggDhJX/RduGweDuuIcPI79M= X-Google-Smtp-Source: ABdhPJxRkfkZrvAxRvFjp6Zlen190OAfO9c/QC6uwVt1GmRyExyB2hyYDvcla47YZFawIBcnYzCkwwLd72cFcPTHs3A= X-Received: by 2002:a9d:2daa:: with SMTP id g39mr2734821otb.77.1603965393472; Thu, 29 Oct 2020 02:56:33 -0700 (PDT) MIME-Version: 1.0 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> <20201022174826.GS1551@shell.armlinux.org.uk> In-Reply-To: From: Ard Biesheuvel Date: Thu, 29 Oct 2020 10:56:22 +0100 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 Mon, 26 Oct 2020 at 09:58, Ard Biesheuvel wrote: > > On Thu, 22 Oct 2020 at 19:59, Ard Biesheuvel wrote: > > > > On Thu, 22 Oct 2020 at 19:48, Russell King - ARM Linux admin > > wrote: > > > > > > 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 wrot= e: > > > > > > > > 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 wrote: > > > > > > > > > >> > > > > > > > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipe= nko 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 Osi= penko wrote: > > > > > > > > > >>>>> The vfp_kmode_exception() function now is unreachab= le 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 t= he issue. > > > > > > > > > >>>> > > > > > > > > > >>>> Eek. Is this with gcc or clang? > > > > > > > > > >>> > > > > > > > > > >>> GCC 9.3.0 > > > > > > > > > >>> > > > > > > > > > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and Au= toFDO input sections") > > > > > > > > > >>>> > > > > > > > > > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add= missing sections") ? > > > > > > > > > >>>> That commit may have implicitly moved the location o= f .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/vf= phw.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 r= estore nor FP exceptions > > > > > > > > > >>>>> and r3, r3, #MODE_MASK @ are supported = in kernel mode > > > > > > > > > >>>>> teq r3, #USR_MODE > > > > > > > > > >>>>> - bne vfp_kmode_exception @ Returns throug= h lr > > > > > > > > > >>>>> + ldr r1, =3Dvfp_kmode_exception > > > > > > > > > >>>>> + bxne r1 @ Returns throug= h lr > > > > > > > > > >>>>> > > > > > > > > > >>>>> VFPFMRX r1, FPEXC @ Is the VFP ena= bled? > > > > > > > > > >>>>> DBGSTR1 "fpexc %08x", r1 > > > > > > > > > >>>> > > > > > > > > > >>>> This seems like a workaround though? I suspect the v= fp11_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=3D9018/1 > > > > > > > > > > > > > > > > > > > > > > > > > > > > The offending commit contains stable tag, so I assume tha= t fixes tag is > > > > > > > > > mandatory. Yours patch misses the fixes tag. > > > > > > > > > > > > > > > > Russell, mind adding that? Or would you like me to update t= he 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. Ther= e'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 whic= h ends up > > > > > > > at the start of the binary, but depending on the compiler, fu= nctions > > > > > > > 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 imp= act on > > > > > > ARM builds, and minimal impact on Thumb2 builds, given that it = retains > > > > > > the exact same semantics as before, but using a different opcod= e. > > > > > > > > > > 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. > > > > > > > True. If 2 bytes of additional opcode are the concern here, we can > > change the current sequence > > > > 6: f093 0f10 teq r3, #16 > > a: f47f affe bne.w 0 > > > > to > > > > 6: 2b10 cmp r3, #16 > > 8: bf18 it ne > > a: f7ff bffe bne.w 0 > > > > which takes up the exact same space. > > BTW this code path looks slightly broken for Thumb-2 in any case: if a > FP exception is taken in kernel mode on a Thumb2 kernel, we enter the > emulation sequence via call_fpe, which will use the wrong set of > value/mask pairs to match the opcode. The minimal fix is to move the > call_fpe label to the right place, but I think it might be better to > move the check for a FP exception in kernel mode to the handling of > __und_svc. Do we have a resolution here? This is causing breakage in kernelci https://kernelci.org/build/id/5f9a834c5ed3c05dd538101b/