From mboxrd@z Thu Jan  1 00:00:00 1970
From: catalin.marinas@arm.com (Catalin Marinas)
Date: Wed, 16 Dec 2015 17:19:05 +0000
Subject: [PATCH v6 09/20] arm64:ilp32: share HWCAP between LP64 and ILP32
In-Reply-To: <20151216165819.GD27051@e104818-lin.cambridge.arm.com>
References: <1450215766-14765-1-git-send-email-ynorov@caviumnetworks.com>
 <1450215766-14765-10-git-send-email-ynorov@caviumnetworks.com>
 <2049962.OV4jWs7vGi@wuerfel>
 <20151216165819.GD27051@e104818-lin.cambridge.arm.com>
Message-ID: <20151216171904.GF27051@e104818-lin.cambridge.arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wed, Dec 16, 2015 at 04:58:20PM +0000, Catalin Marinas wrote:
> 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.

IIUC, we may have a problem with this. elf_hwcap is 64-bit long while
elf_info[n] is 32-bit (Elf32_Addr), so we truncate AT_HWCAP if we ever
go beyond bit 31. The above may need to look something like:

#define COMPAT_ELF_HWCAP	\
	(is_a32_compat_task()	\
	 ? compat_elf_hwcap	\
	 : (u32)elf_hwcap)

#define COMPAT_ELF_HWCAP2	\
	(is_a32_compat_task()	\
	 ? compat_elf_hwcap2	\
	 : (u32)(elf_hwcap >> 32))

-- 
Catalin