linux-kernel - Re: [PATCH 17/22] arm64: vdso: disable LTO

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Message-ID: <20200624215231.GC120457@google.com>
Date:   Wed, 24 Jun 2020 14:52:31 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Will Deacon <will@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [PATCH 17/22] arm64: vdso: disable LTO

On Wed, Jun 24, 2020 at 01:58:57PM -0700, 'Nick Desaulniers' via Clang Built Linux wrote:
> On Wed, Jun 24, 2020 at 1:33 PM Sami Tolvanen <samitolvanen@...gle.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?

I recall the compiler optimizing away functions at some point, but as
LTO is not really needed in the vDSO, it's just easiest to disable it
there.

Sami