linux-hardening - Re: [PATCH] gcc-plugins: simplify GCC plugin-dev capability test

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Date:   Wed, 20 Jan 2021 04:01:19 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Jon Hunter <jonathanh@...dia.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Emese Revfy <re.emese@...il.com>,
        linux-hardening@...r.kernel.org,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH] gcc-plugins: simplify GCC plugin-dev capability test

On Wed, Jan 20, 2021 at 2:48 AM Thierry Reding <thierry.reding@...il.com> wrote:
>
> On Fri, Dec 18, 2020 at 08:33:37PM +0000, Jon Hunter wrote:
> >
> > On 18/12/2020 17:54, Linus Torvalds wrote:
> > > On Fri, Dec 18, 2020 at 7:33 AM Jon Hunter <jonathanh@...dia.com> wrote:
> > >>
> > >> However, if you are saying that this is a problem/bug with our builders,
> > >> then of course we will have to get this fixed.
> > >
> > > This seems to be a package dependency problem with the gcc plugins -
> > > they clearly want libgmp, but apparently the package hasn't specified
> > > that dependency.
> > >
> > > If this turns out to be a big problem, I guess we can't simplify the
> > > plugin check after all.
> > >
> > > We historically just disabled gcc-plugins if that header didn't build,
> > > which obviously meant that it "worked" for people, but it also means
> > > that clearly the coverage can't have been as good as it could/should
> > > be.
> > >
> > > So if it's as simple as just installing the GNU multiprecision
> > > libraries ("gmp-devel" on most rpm-based systems, "libgmp-dev" on most
> > > debian systems), then I think that's the right thing to do. You'll get
> > > a working build again, and equally importantly, your build servers
> > > will actually do a better job of covering the different build options.
> >
> >
> > Thanks. I have reported this issue to the team that administers the
> > builders. So hopefully, they will install the necessary packages for us
> > now.
>
> Just to close the loop on this, the builders now have libgmp-dev and
> libmpc-dev packages installed and the builds are passing without the
> workaround we had used.
>
> Thierry


I was slightly concerned about your question:

"In case where CC != HOSTCC, it's possible that CC was not built against
the same version of GMP/MPC as HOSTCC. And even HOSTCC might not
necessarily have been built against the versions provided by libgmp-dev
or libmpc-dev. I'm not overly familiar with GMP/MPC, so perhaps if these
headers are reasonably stable, this is not all that important. But if it
is, then which version of GMP/MPC do we need? The version that CC was
built against, or the version that HOSTCC was built against?"



I do not have a good insight about this.

I am not sure if it is perfectly OK to
use gmp.h from HOSTCC when it was not bundled with CC.

The version difference might not be a significant issue, though...





-- 
Best Regards
Masahiro Yamada