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Date:   Wed, 24 Jun 2020 16:51:44 -0700
From:   Andi Kleen <ak@linux.intel.com>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Sami Tolvanen <samitolvanen@google.com>,
        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>
Subject: Re: [PATCH 17/22] arm64: vdso: disable LTO
Message-ID: <20200624235144.GD818054@tassilo.jf.intel.com>
References: <20200624203200.78870-1-samitolvanen@google.com>
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On Wed, Jun 24, 2020 at 02:09:40PM -0700, Nick Desaulniers wrote:
> 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

I think I did it originally because the vDSO linker step didn't do
all the magic needed for gcc LTO. But it also doesn't seem to be
very useful for just a few functions that don't have complex
interactions, and somewhat risky for violating some assumptions.

-Andi