linux-kernel - Re: [PATCH 11/18] arm64: ilp32: share aarch32 syscall handlers

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Message-ID: <20161205171242.GH14429@e104818-lin.cambridge.arm.com>
Date:   Mon, 5 Dec 2016 17:12:43 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Yury Norov <ynorov@...iumnetworks.com>
Cc:     arnd@...db.de, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arch@...r.kernel.org, szabolcs.nagy@....com,
        heiko.carstens@...ibm.com, cmetcalf@...hip.com,
        philipp.tomsich@...obroma-systems.com, joseph@...esourcery.com,
        zhouchengming1@...wei.com, Prasun.Kapoor@...iumnetworks.com,
        agraf@...e.de, geert@...ux-m68k.org, kilobyte@...band.pl,
        manuel.montezelo@...il.com, pinskia@...il.com,
        linyongting@...wei.com, klimov.linux@...il.com, broonie@...nel.org,
        bamvor.zhangjian@...wei.com, maxim.kuvyrkov@...aro.org,
        Nathan_Lynch@...tor.com, schwidefsky@...ibm.com,
        davem@...emloft.net, christoph.muellner@...obroma-systems.com
Subject: Re: [PATCH 11/18] arm64: ilp32: share aarch32 syscall handlers

On Fri, Oct 21, 2016 at 11:33:10PM +0300, Yury Norov wrote:
> off_t is  passed in register pair just like in aarch32.
> In this patch corresponding aarch32 handlers are shared to
> ilp32 code.
[...]
> +/*
> + * Note: off_4k (w5) is always in units of 4K. If we can't do the
> + * requested offset because it is not page-aligned, we return -EINVAL.
> + */
> +ENTRY(compat_sys_mmap2_wrapper)
> +#if PAGE_SHIFT > 12
> +	tst	w5, #~PAGE_MASK >> 12
> +	b.ne	1f
> +	lsr	w5, w5, #PAGE_SHIFT - 12
> +#endif
> +	b	sys_mmap_pgoff
> +1:	mov	x0, #-EINVAL
> +	ret
> +ENDPROC(compat_sys_mmap2_wrapper)

For compat sys_mmap2, the pgoff argument is in multiples of 4K. This was
traditionally used for architectures where off_t is 32-bit to allow
mapping files to 2^44.

Since off_t is 64-bit with AArch64/ILP32, should we just pass the off_t
as a 64-bit value in two different registers (w5 and w6)?

-- 
Catalin