On Wednesday 11 May 2016 11:04:38 Yury Norov wrote:

On Wed, May 11, 2016 at 10:04:16AM +0800, Zhangjian (Bamvor) wrote:
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Ok, I will test the ltp syscall test.
With this changes, the issue I mentioned should be fixed. But we still
use mmap2 syscall for ILP32 application when we pass the offset instead
of page offset. Is it correct?

I don't remember. It's probably not important whether we have the shift
in there, as long as it's independent of the actual kernel page size and
user space and kernel agree on the calling conventions.

Well. I am ok with where to shift the pages size because we get the same
result. I was just thinking if we should get rid of the name of mmap2 in our
ILP32 porting. Actually, it is mmap but we name it as mmap2. User may confused
if they do not know the implementations.

This is what generic unistd.h does. If you want to change it, you'd
change each arch that uses generic unistd.h.

Generic unistd.h has this:

#ifdef __SYSCALL_COMPAT
#define __SC_COMP_3264(_nr, _32, _64, _comp) __SYSCALL(_nr, _comp)
#else
#define __SC_COMP_3264(_nr, _32, _64, _comp) __SC_3264(_nr, _32, _64)
#endif

#define __NR3264_mmap 222
__SC_3264(__NR3264_mmap, sys_mmap2, sys_mmap)


#if __BITS_PER_LONG == 64 && !defined(__SYSCALL_COMPAT)
#define __NR_mmap __NR3264_mmap
#else
#define __NR_mmap2 __NR3264_mmap
#endif

So by default we get __NR_mmap2 and sys_mmap2 on 32-bit ABIs, but
__NR_mmap and sys_mmap on 64-bit ABIs, as it should be.

The problem is that arch/arm64/kernel/sys_ilp32.c now overrides
this to use __NR_mmap2 with sys_mmap, so we have a mismatch. I think
we should either override both the implementation and the number,
or neither of them.

I think what happened is that you chose to override sys_mmap because
sys_mmap2 sometimes takes an off_t argument, however the kernel
just treats it as 'unsigned long', with a range of 44 bits for the
offset. Using sys_mmap with a __kernel_loff_t argument gives
us 64-bit range, but if we do that, I think it should be __NR_mmap.

	Arnd