linux-kernel - Re: [PATCH] arm64: Allow disabling of the compat vDSO

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Message-ID: <CAKwvOdk2KzXfLzKgMvmQsss_-CchE_dhWc7Sy24DUu8r+Ryg_Q@mail.gmail.com>
Date:   Thu, 26 Sep 2019 09:38:34 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Vincenzo Frascino <vincenzo.frascino@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] arm64: Allow disabling of the compat vDSO

On Thu, Sep 26, 2019 at 12:47 AM Catalin Marinas
<catalin.marinas@....com> wrote:
>
> On Thu, Sep 26, 2019 at 01:06:50AM +0100, Vincenzo Frascino wrote:
> > On 9/25/19 6:08 PM, Catalin Marinas wrote:
> > > On Wed, Sep 25, 2019 at 09:53:16AM -0700, Nick Desaulniers wrote:
> > >> On Wed, Sep 25, 2019 at 6:09 AM Catalin Marinas <catalin.marinas@....com> wrote:
> > >>> Suggestions for future improvements of the compat vDSO handling:
> > >>>
> > >>> - replace the CROSS_COMPILE_COMPAT prefix with a full COMPATCC; maybe
> > >>>   check that it indeed produces 32-bit code
> >
> > CROSS_COMPILE_COMPAT is called like this for symmetry with CROSS_COMPILE.
>
> Actually, what gets in the way is the CONFIG_CROSS_COMPILE_COMPAT_VDSO.
> We can keep CROSS_COMPILE_COMPAT together with COMPATCC initialised to
> $(CROSS_COMPILE_COMPAT)gcc. When we will be able to build the compat
> vDSO with clang, we just pass COMPATCC=clang on the make line and the
> kernel Makefile will figure out the --target option from
> CROSS_COMPILE_COMPAT (see how CLANG_FLAGS is handled).
>
> If we stick only to env variables or make cmd line (without Kconfig) for
> the compiler name, we can add a COMPATCC_IS_CLANG in the Kconfig
> directly and simply not allow the enabling the COMPAT_VDSO if we don't
> have the right compiler. This saves us warnings during build.

Yes, I think this would be a nice approach.
-- 
Thanks,
~Nick Desaulniers