Date: Wed, 16 Dec 2015 16:58:20 +0000
From: Catalin Marinas <catalin.marinas@arm.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Yury Norov <ynorov@caviumnetworks.com>, pinskia@gmail.com,
        Prasun.Kapoor@caviumnetworks.com, Nathan_Lynch@mentor.com,
        linux-kernel@vger.kernel.org, agraf@suse.de,
        Andrew Pinski <apinski@cavium.com>, klimov.linux@gmail.com,
        Andrew Pinski <Andrew.Pinski@caviumnetworks.com>, broonie@kernel.org,
        jan.dakinevich@gmail.com, joseph@codesourcery.com,
        ddaney.cavm@gmail.com, schwab@suse.de, bamvor.zhangjian@huawei.com,
        philipp.tomsich@theobroma-systems.com,
        linux-arm-kernel@lists.infradead.org,
        christoph.muellner@theobroma-systems.com
Subject: Re: [PATCH v6 09/20] arm64:ilp32: share HWCAP between LP64 and ILP32
Message-ID: <20151216165819.GD27051@e104818-lin.cambridge.arm.com>
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On Wed, Dec 16, 2015 at 04:54:34PM +0100, Arnd Bergmann wrote:
> On Wednesday 16 December 2015 00:42:35 Yury Norov wrote:
> > 
> >  #ifdef CONFIG_COMPAT
> > -#define COMPAT_ELF_HWCAP       (compat_elf_hwcap)
> > -#define COMPAT_ELF_HWCAP2      (compat_elf_hwcap2)
> >  extern unsigned int compat_elf_hwcap, compat_elf_hwcap2;
> > +#define COMPAT_ELF_HWCAP       \
> > +       (is_a32_compat_task()   \
> > +         ? compat_elf_hwcap    \
> > +         : elf_hwcap)
> > +
> > +#define COMPAT_ELF_HWCAP2      \
> > +       (is_a32_compat_task()   \
> > +         ? compat_elf_hwcap2   \
> > +         : 0)
> > +
> >  #endif
> 
> I'm trying to understand how this is used. Are you compiling
> fs/compat_binfmt_elf.c twice to handle both 32-bit ELF types?

It's the same compat_binfmt_elf.c which handles all 32-bit ELF types,
i.e. AArch32 and A64/ILP32. The above macros are not constants, so they
are evaluated every time a new ELF file is loaded. We do a similar trick
with COMPAT_SET_PERSONALITY in patch 11.

-- 
Catalin
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