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Date:   Tue, 17 Mar 2020 17:00:05 +0100
From:   Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
To:     Christophe Leroy <christophe.leroy@c-s.fr>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 16/46] powerpc/mm: Allocate static page tables for
 fixmap
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On Tue, Mar 17, 2020 at 03:38:46PM +0100, Christophe Leroy wrote:
> > diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
> > index f62de06e3d07..9934659cb871 100644
> > --- a/arch/powerpc/mm/pgtable_32.c
> > +++ b/arch/powerpc/mm/pgtable_32.c
> > @@ -29,11 +29,27 @@
> >   #include <asm/fixmap.h>
> >   #include <asm/setup.h>
> >   #include <asm/sections.h>
> > +#include <asm/early_ioremap.h>
> >   #include <mm/mmu_decl.h>
> >   extern char etext[], _stext[], _sinittext[], _einittext[];
> > +static u8 early_fixmap_pagetable[FIXMAP_PTE_SIZE] __page_aligned_data;
> 
> Sparse reports this as a variable size array. This is definitely not. Gcc
> properly sees it is an 8k table (2 pages).

Yes, thing is that FIXMAP_PTE_SIZE is not that constant since it uses
__builtin_ffs() (via PTE_SHIFT / PTE_T_LOG2).
Nevertheless, since Sparse v0.6.1 (released in October) accepts these
in constant expressions, like GCC does.

-- Luc