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From: Arnd Bergmann <arnd@arndb.de>
To: linux-arm-kernel@lists.infradead.org
Cc: Alexander Graf <agraf@suse.de>, Will Deacon <will.deacon@arm.com>,
        Catalin Marinas <Catalin.Marinas@arm.com>, Michael Matz <matz@suse.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Dirk =?ISO-8859-1?Q?M=FCller?= <dmueller@suse.com>,
        Suravee Suthikulanit <suravee.suthikulpanit@amd.com>,
        Andreas Schwab <schwab@suse.de>
Subject: Re: [PATCH] arm64: Enable CONFIG_COMPAT also for 64k page size
Date: Wed, 11 Mar 2015 13:47:36 +0100
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On Wednesday 11 March 2015 06:24:16 Alexander Graf wrote:
> So after recompiling all of the distribution with newer binutils we now
> have an openSUSE Factory tree that has 64k aligned 32bit binaries.
> 
> Unfortunately however, the 32bit glibc has a bogus mmap() implementation
> that hard codes 4k page size.
> 
> With the patch below applied to glibc, I can successfully run 32bit user
> space on Seattle with 64k PAGE_SIZE though. So I guess we'll need to fix
> up glibc next.
> 
> Do you know of anyone who's fluent enough in 32bit ARM assembly to
> convert the hard coded assumptions in there to instead use a variable
> that takes the actual host page size into account?

I believe this is a kernel bug, and the kernel API for 32-bit emulation
should always take the pgoff argument in 4KB units instead of PAGE_SIZE
units, see the implementation of sys_mmap2 in
arch/powerpc/kernel/sys_ppc32.c.

All user space programs that call mmap2 still need to make sure that
their arguments are PAGE_SIZE aligned, but the libc need not care
about this here.

	Arnd