Re: [PATCH V9 21/21] csky: support dword access for get_user_size()

[Arnd Bergmann]

On Tue, Oct 16, 2018 at 5:33 AM Guo Ren <ren_guo@xxxxxxxxx> wrote:
>
> Support dword access for get_user_size and redesign put_user_size with
> the same style of get_user_size. It's Ok to use xxx_user_asm_common for
> all size of variable with ldb, ldh, ldw, ld.d
>
> ld.d rx, (addr, 0) could "rx <= addr" "and r(x+1) <= addr+4" and this also
> follow abiv2 gcc ABI for dword access.

Are you sure this is correct for this?

static inline u32 get_64_to_32(__u64 __user *p)
{
      u32 ret;
      get_user(ret, p);
      return ret;
}

If I read __get_user_asm_common() right, the ld.d would overwrite
two registers, but the caller only expects one, so it clobbers one
that might be in use.

     Arnd