Re: RFD: x32 ABI system call numbers

[Avi Kivity <avi@redhat.com>]

On 08/31/2011 08:09 PM, H. Peter Anvin wrote:
> >  I really think that "x32" should try to aim *VERY* hard at using the
> >  64-bit system calls, and seeing itself as being a "32-bit application
> >  in a 64-bit world".  That's not just true for time_t (which I think
> >  should be 64-bit on anything new that expects to survive for any
> >  amount of time), but in general.
>
> We're trying for it.  The things we're trying to avoid is to muck (too
> much) with the compat layer for the mega-multiplex system calls like
> ioctl.  We can't just use the 64-bit ioctl because ioctl structures
> generally contain pointers.
>

     struct iovec
     {
         void __user *iov_base;    /* BSD uses caddr_t (1003.1g requires 
void *) */
         __kernel_size_t iov_len; /* Must be size_t (1003.1g) */
     } __attribute__((x32_abi_64));

     typedef long time_t __attribute__((x32_abi_64));

The x32_abi_64 attribute converts pointers and longs back to 64-bit and 
adjusts the alignment accordingly.  If we tag all userspace visible 
structures with this attribute, we can use the 64-bit ABI without changes.

Issues:
&my_iovec->iov_base yields something that is not a void ** (reads of a 
64-bit pointer decay to a 32-bit pointer, writes zero extend).
   printf formats will break
   if someone embeds an iovec in a structure, it will occupy more space 
than expected


-- 
error compiling committee.c: too many arguments to function