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

[Yury Norov]

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?