Re: RFC: Add 32bit x86-64 support to binutils

[David Daney <ddaney at caviumnetworks dot com>]

On 12/30/2010 12:12 PM, H. Peter Anvin wrote:
> On 12/30/2010 11:34 AM, David Daney wrote:
> > My suggestion:  Since people already spend a great deal of effort
> > maintaining the existing i386 compatible Linux syscall infrastructure,
> > make your new 32-bit x86-64 Linux syscall ABI identical to the existing
> > i386 syscall ABI.  This means that the psABI must use the same size and
> > alignment rules for in-memory structures as the i386 does.
>
> No, it doesn't.  It just means it need to do so *for the types used by
> the kernel*.  The kernel uses types like __u64, which would indeed have
> to be declared aligned(4).

Some legacy interfaces don't use fixed width types.  There almost 
certainly are some ioctls that don't use your fancy __u64.

Then there are things like ppoll() that take a pointer to:

           struct timespec {
               long    tv_sec;         /* seconds */
               long    tv_nsec;        /* nanoseconds */
           };

There are no fields in there that are controlled by __u64 either. 
Admittedly this case might not differ between the two 32-bit ABIs, but 
it shows that __u64/__u32 are not universally used in the Linux syscall 
ABIs.

If you are happy with potential memory layout differences between the 
two 32-bit ABIs, then don't specify that they are the same.  But don't 
claim that use of __u64/__u32 covers all cases.

David Daney