linux-kernel - Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it

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Date:	Wed, 2 Dec 2015 13:01:53 +0300
From:	Yury Norov <ynorov@...iumnetworks.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<catalin.marinas@....com>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <pinskia@...il.com>,
	<ddaney.cavm@...il.com>, <jan.dakinevich@...il.com>,
	<Prasun.Kapoor@...iumnetworks.com>,
	<christoph.muellner@...obroma-systems.com>,
	<philipp.tomsich@...obroma-systems.com>, <broonie@...nel.org>,
	<andrey.konovalov@...aro.org>, <Nathan_Lynch@...tor.com>,
	<agraf@...e.de>, <bamvor.zhangjian@...wei.com>,
	<klimov.linux@...il.com>, <joseph@...esourcery.com>,
	<schwab@...e.de>
Subject: Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate
 table (in entry.S) to use it

On Tue, Nov 17, 2015 at 10:57:52PM +0100, Arnd Bergmann wrote:

It looks, all them are needed.

> > +asmlinkage long compat_sys_mmap2_wrapper(void);
> > +#define sys_mmap2                      compat_sys_mmap2_wrapper

This wrapper checks alignement of pgoff, if page sise is greater than
4K

> > +asmlinkage long compat_sys_fstatfs64_wrapper(void);
> > +#define compat_sys_fstatfs64    compat_sys_fstatfs64_wrapper
> > +asmlinkage long compat_sys_statfs64_wrapper(void);
> > +#define compat_sys_statfs64             compat_sys_statfs64_wrapper

This two hacks fix an alignment issue. I didn't check all details but
it looks like sizeof(compat_statfs64) is different in kernel and library.
And this size is passed as 2nd argument to compat syscalls. We can
handle it in userspace but I don't see any advantage. 

All this handlers are shared between ilp32 and aarch32.
This is best we came up, as it doesn't add new hacks, but reuses old
ones...
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