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Date:   Wed, 7 Aug 2019 13:16:58 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Steven Price <steven.price@arm.com>
Cc:     Mark Rutland <Mark.Rutland@arm.com>, x86@kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
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        =?ISO-8859-1?Q?J=E9r=F4me?= Glisse <jglisse@redhat.com>,
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        Andy Lutomirski <luto@kernel.org>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        "Liang, Kan" <kan.liang@linux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v10 20/22] x86: mm: Convert dump_pagetables to use
 walk_page_range
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On Wed, 7 Aug 2019 13:58:21 +0100 Steven Price <steven.price@arm.com> wrote:

> > ./arch/x86/include/asm/pgtable_64_types.h:56:22: error: initializer element is not constant
> >  #define PTRS_PER_PGD 512
> >                       ^
> 
> This is very unhelpful of GCC - it's actually PTRS_PER_P4D which isn't
> constant!

Well.  You had every right to assume that an all-caps macro is a
compile-time constant.

We are innocent victims of Kirill's c65e774fb3f6af2 ("x86/mm: Make
PGDIR_SHIFT and PTRS_PER_P4D variable") which lazily converted these
macros into runtime-only, under some Kconfig settings.  It should have
changed those macros into static inlined lower-case functions.