[PATCH 11/18] arm64: ilp32: share aarch32 syscall handlers

Yury Norov
2016-12-06T07:32:57Z

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