linux-kernel - Re: [PATCH 20/25] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it

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Message-ID: <20160512125909.GA29077@yury-N73SV>
Date:	Thu, 12 May 2016 15:59:09 +0300
From:	Yury Norov <ynorov@...iumnetworks.com>
To:	"Zhangjian (Bamvor)" <bamvor.zhangjian@...wei.com>
CC:	Arnd Bergmann <arnd@...db.de>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-doc@...r.kernel.org>,
	Andrew Pinski <Andrew.Pinski@...iumnetworks.com>,
	<catalin.marinas@....com>, <heiko.carstens@...ibm.com>,
	Hanjun Guo <guohanjun@...wei.com>, <joseph@...esourcery.com>,
	<linux-arch@...r.kernel.org>, <linux-s390@...r.kernel.org>,
	"jijun (D)" <jijun2@...wei.com>,
	<Prasun.Kapoor@...iumnetworks.com>, <schwab@...e.de>,
	<agraf@...e.de>, <pinskia@...il.com>, <klimov.linux@...il.com>,
	<broonie@...nel.org>, <Nathan_Lynch@...tor.com>,
	<linux-kernel@...r.kernel.org>, Andrew Pinski <apinski@...ium.com>,
	<schwidefsky@...ibm.com>,
	<christoph.muellner@...obroma-systems.com>
Subject: Re: [PATCH 20/25] arm64:ilp32: add sys_ilp32.c and a separate table
 (in entry.S) to use it

On Thu, May 12, 2016 at 08:52:46PM +0800, Zhangjian (Bamvor) wrote:
> Hi,
> 
> On 2016/5/12 16:24, Yury Norov wrote:
> >On Thu, May 12, 2016 at 11:45:53AM +0800, Zhangjian (Bamvor) wrote:
> >
> >[...]
> >
> >>>Hmm, that is indeed tricky. I think COMPAT_SYSCALL_WRAP4 rightfully
> >>>refuses the loff_t argument here, as the common case is that this is
> >>>not possible.
> >>It works if I apply the following patch, I defined the wrong `__TYPE_IS_xxx`
> >>yesterday. Should we merge this into ILP32 series or send the compat.h
> >>and syscalls.h individually? The current series of ILP32 is a little bit
> >>long and hard to review.
> >>diff --git a/include/linux/compat.h b/include/linux/compat.h
> >>index ba6ebe0..22a9565 100644
> >>--- a/include/linux/compat.h
> >>+++ b/include/linux/compat.h
> >>@@ -747,7 +747,8 @@ asmlinkage long compat_sys_fanotify_mark(int, unsigned int, __u32, __u32,
> >>  #ifndef __SC_COMPAT_CAST
> >>  #define __SC_COMPAT_CAST(t, a) ({                                      \
> >>         BUILD_BUG_ON((sizeof(t) > 4) && !__TYPE_IS_L(t) &&              \
> >>-                    !__TYPE_IS_UL(t) && !__TYPE_IS_PTR(t));            \
> >>+                    !__TYPE_IS_UL(t) && !__TYPE_IS_PTR(t) &&           \
> >>+                    !__TYPE_IS_LOFFT(t));                              \
> >
> >I think it's wrong, as loff_t is 64-bit in 32-bit userspace, and this
> >will clear meaningful data in top halve.
> Yes. It is my fault. The original thoughts is clear the up 32bit for size_t.
> How should we skip the loff_t?
> 
> Regards
> 
> Bamvor

I already suggested:

For cases like this I think we should write wrappers by hands. In
unistd.h we can use __SC_WRAP, so they will work like wrappers
generated by COMPAT_SYSCALL_WRAPx()

Do you see any downsides?