linux-kernel - Re: [PATCH] arm64: Enable CONFIG

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Message-ID: <5396604.TRferrWZgF@wuerfel>
Date:	Wed, 11 Mar 2015 13:47:36 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Alexander Graf <agraf@...e.de>, Will Deacon <will.deacon@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Michael Matz <matz@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dirk Müller <dmueller@...e.com>,
	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	Andreas Schwab <schwab@...e.de>
Subject: Re: [PATCH] arm64: Enable CONFIG_COMPAT also for 64k page size

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
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