linux-hardening - Re: [PATCH RESEND] gcc-plugins: avoid errors with -std=gnu++11 on old gcc

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Message-ID: <282490.1616047333@turing-police>
Date:   Thu, 18 Mar 2021 02:02:13 -0400
From:   "Valdis Klētnieks" <valdis.kletnieks@...edu>
To:     Kees Cook <keescook@...omium.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-hardening@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] gcc-plugins: avoid errors with -std=gnu++11 on old gcc

On Wed, 17 Mar 2021 22:52:56 -0700, Kees Cook said:
> On Mon, Mar 08, 2021 at 03:40:21AM -0500, Valdis Kl��tnieks wrote:
> > It turns out that older gcc (4.9 and 5.4) have gnu++11 support, but
> > due to a gcc bug fixed in gcc6, throw errors during the build.
> > The relevant gcc bug is https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69959
> >
> > Version the option based on what gcc we're using.
>
> Is there a better way to detect this than with version checking?

Not really.  gcc 11 needs --std=gnu++11 to build it.  And although
gcc4 and gcc5 *claim* to support it, there's a known bug, so we *can't*
feed gnu++11 to them.  We can check versions..

Or heave gcc-plugins over the side entirely..
Or declare that gcc6 is the minimum for building the kernel.

But if we support gcc4/5 *and* gcc11 to build gcc-plugins, we have to version-check.

(Unrelated - the patch has grown a merge conflict since I sent it, let me
know if you want an updated one, or if it's OK as is....

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