Date: Tue, 6 Dec 2016 13:02:57 +0530
From: Yury Norov <ynorov@caviumnetworks.com>
To: Catalin Marinas <catalin.marinas@arm.com>
CC: <arnd@arndb.de>, <linux-arm-kernel@lists.infradead.org>,
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Subject: Re: [PATCH 11/18] arm64: ilp32: share aarch32 syscall handlers
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On Mon, Dec 05, 2016 at 05:12:43PM +0000, Catalin Marinas wrote:
> 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)?

Current glibc implementation becomes broken for 64-bit off_t if
if I'll do what you want.
sysdeps/unix/sysv/linux/generic/wordsize-32/mmap.c
28 __ptr_t
29 __mmap (__ptr_t addr, size_t len, int prot, int flags, int fd, off_t offset)
30 {
31   if (offset & (MMAP_PAGE_UNIT - 1))
32     {
33       __set_errno (EINVAL);
34       return MAP_FAILED;
35     }
36   return (__ptr_t) INLINE_SYSCALL (mmap2, 6, addr, len, prot, flags, fd,
37                                    offset / MMAP_PAGE_UNIT);
38 }
39 
40 weak_alias (__mmap, mmap)

So it requires changes both in glibc and in kernel. I can do it. But
I'd like to collect opinions of kernel and glibc developers before
starting it. 

Yury