From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kbuild-owner@vger.kernel.org>
Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56318 "EHLO
        lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S2389958AbgFXVJx (ORCPT
        <rfc822;linux-kbuild@vger.kernel.org>);
        Wed, 24 Jun 2020 17:09:53 -0400
Received: from mail-pf1-x441.google.com (mail-pf1-x441.google.com [IPv6:2607:f8b0:4864:20::441])
        by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 541DFC061796
        for <linux-kbuild@vger.kernel.org>; Wed, 24 Jun 2020 14:09:53 -0700 (PDT)
Received: by mail-pf1-x441.google.com with SMTP id p11so1786281pff.11
        for <linux-kbuild@vger.kernel.org>; Wed, 24 Jun 2020 14:09:53 -0700 (PDT)
MIME-Version: 1.0
References: <20200624203200.78870-1-samitolvanen@google.com>
 <20200624203200.78870-18-samitolvanen@google.com> <CAKwvOdnEbCfYZ9o=OF51oswyqDvN4iP-9syWUDhxfueq4q0xcw@mail.gmail.com>
In-Reply-To: <CAKwvOdnEbCfYZ9o=OF51oswyqDvN4iP-9syWUDhxfueq4q0xcw@mail.gmail.com>
From: Nick Desaulniers <ndesaulniers@google.com>
Date: Wed, 24 Jun 2020 14:09:40 -0700
Message-ID: <CAKwvOdm_EBfmV+GvDE-COoDwpEm9snea4_KtuFyorA5KEU6FbQ@mail.gmail.com>
Subject: Re: [PATCH 17/22] arm64: vdso: disable LTO
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kbuild-owner@vger.kernel.org
List-ID: <linux-kbuild.vger.kernel.org>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>, Will Deacon <will@kernel.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, "Paul E. McKenney" <paulmck@kernel.org>, Kees Cook <keescook@chromium.org>, clang-built-linux <clang-built-linux@googlegroups.com>, Kernel Hardening <kernel-hardening@lists.openwall.com>, linux-arch <linux-arch@vger.kernel.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>, linux-pci@vger.kernel.org, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>, Andi Kleen <ak@linux.intel.com>

On Wed, Jun 24, 2020 at 1:58 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Wed, Jun 24, 2020 at 1:33 PM Sami Tolvanen <samitolvanen@google.com> wrote:
> >
> > Filter out CC_FLAGS_LTO for the vDSO.
>
> Just curious about this patch (and the following one for x86's vdso),
> do you happen to recall specifically what the issues with the vdso's
> are?

+ Andi (tangential, I actually have a bunch of tabs open with slides
from http://halobates.de/ right now)
58edae3aac9f2
67424d5a22124
$ git log -S DISABLE_LTO

>
> >
> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > ---
> >  arch/arm64/kernel/vdso/Makefile | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> > index 556d424c6f52..cfad4c296ca1 100644
> > --- a/arch/arm64/kernel/vdso/Makefile
> > +++ b/arch/arm64/kernel/vdso/Makefile
> > @@ -29,8 +29,8 @@ ldflags-y := -shared -nostdlib -soname=linux-vdso.so.1 --hash-style=sysv \
> >  ccflags-y := -fno-common -fno-builtin -fno-stack-protector -ffixed-x18
> >  ccflags-y += -DDISABLE_BRANCH_PROFILING
> >
> > -CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS)
> > -KBUILD_CFLAGS                  += $(DISABLE_LTO)
> > +CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS) \
> > +                               $(CC_FLAGS_LTO)
> >  KASAN_SANITIZE                 := n
> >  UBSAN_SANITIZE                 := n
> >  OBJECT_FILES_NON_STANDARD      := y
> > --

-- 
Thanks,
~Nick Desaulniers