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

[Arnd Bergmann]

On Thursday 12 May 2016 20:49:24 Zhangjian wrote:
> Hi,
> 
> On 2016/5/12 17:21, Arnd Bergmann wrote:
> > On Thursday 12 May 2016 10:17:58 Catalin Marinas wrote:
> >> On Wed, May 11, 2016 at 09:30:07PM +0200, Arnd Bergmann wrote:
> >>> On Wednesday 11 May 2016 17:59:01 Catalin Marinas wrote:
> >>>
> >>> I don't think the shifts are a problem, the main downside would be
> >>> the limit to 44 bits of file offsets (16TB files), but it's also
> >>> unclear if that is a practical problem at all. If it is, we run
> >>> into the same problem on all other 32-bit architectures too.
> >>
> >> I hope people are seriously thinking of moving to an LP64 ABI if they
> >> have such large file offset needs.
> >
> > Good point. 44 bits of file size is certainly enough for mmap()
> > on a 32-bit task: you would only be able to map a very small fraction
> > of the file anyway, and if you want to map larger files, and should
> > move to 64-bit tasks long before this becomes a limitation.
> Hi,
> 
> I apply the following patch in order to make use of the REAL mmmap2. LTP
> test pass in litle endian. mmap16 successful with segfault in big endian.
> 
> BTW, I saw the similar code in tile, mips, microblaze and s390 compat. Should
> we merge these code into a common syscall wrapper?

I think that's a good idea. The function used to be slightly different
for each architecture, but now it seems we have a significant number
of identical implementations that we could just merge them together
into one.

sys_mmap_pgoff was originally introduced as the common implementation
and it reduced the amount of duplication a lot, but as its units
are based on PAGE_SIZE rather than hardwired 4096 bytes, it's
not as useful.

> diff --git a/arch/arm64/kernel/sys_ilp32.c b/arch/arm64/kernel/sys_ilp32.c
> index d85fe94..2cd72eb 100644
> --- a/arch/arm64/kernel/sys_ilp32.c
> +++ b/arch/arm64/kernel/sys_ilp32.c
> @@ -41,7 +41,16 @@
>   #define compat_sys_sync_file_range     sys_sync_file_range
>   #define compat_sys_truncate64          sys_truncate
>   #define sys_llseek                     sys_lseek
> -#define sys_mmap2                     sys_mmap
> +
> +SYSCALL_DEFINE6(mmap2, unsigned long, addr, unsigned long, len,
> +       unsigned long, prot, unsigned long, flags, unsigned long, fd,
> +       unsigned long, pgoff)
> +{
> +       if (pgoff & (~PAGE_MASK >> 12))
> +               return -EINVAL;
> +
> +       return sys_mmap_pgoff(addr, len, prot, flags, fd, pgoff >> (PAGE_SHIFT-12));
> +}
> 

Looks good to me.

	Arnd