linux-kernel - Re: [PATCH v4 2/2] x86/purgatory: Make sure we fail the build if purgatory.ro has missing symbols

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Date:   Fri, 13 Mar 2020 19:06:58 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Hans de Goede <hdegoede@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] x86/purgatory: Make sure we fail the build if
 purgatory.ro has missing symbols

On Fri, Mar 13, 2020 at 12:42:36AM -0400, Arvind Sankar wrote:
>  The real problem is that there exist CFLAGS that should be used for
> all source files in the kernel, and there are CFLAGS (eg tracing,
> stack check etc) that should only be used for the kernel proper. For
> special compilations, such as boot stubs, vdso's, purgatory we should
> have the generic CFLAGS but not the kernel-proper CFLAGS. The issue
> currently is that these special compilations need to filter out all
> the flags added for kernel-proper, and this is a moving target as
> more tracing/sanity flags get added. Neither the solution of simply
> re-initializing CFLAGS (which will miss generic CFLAGS) nor trying to
> filter out CFLAGS (which will miss new kernel-proper CFLAGS) works
> very well. I think ideally splitting these into independent variables,
> i.e. BASE_FLAGS that can be used for everything, and KERNEL_FLAGS
> only to be used for the kernel proper is likely eventually the better
> solution, rather than conflating both into KBUILD_CFLAGS.

Hohumm, this has come up a bunch of times in the past in conjunction
with boot/{,compressed/} Makefiles too. I'd be open towards reworking
this properly but I'm afraid it would cause a lot of churn and breakage
and it is hard to say how ugly it would become before someone actually
tries it. ;-\

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette