Re: s390x ffi_closure_helper_SYSV

["Ulrich Weigand" <uweigand@de.ibm.com>]

Hi Richard,

> thx for your reply. I agree that it makes sense to return a full ffi_arg
> if the integral value is smaller than the machine register.

It's not a matter of what makes sense, it's a matter of what libffi
*expects the user-provided callback to do*.  If the *callback* doesn't
fill in a full ffi_arg, then libffi will not operate correctly.

> The program pollutes a fairly large junk of memory below the frame
> pointer and then calls back to a python function (from c).
> Because the ret_buffer variable (in ffi_closure_helper_SYSV) is not
> initialized properly, the returned value is not the same on s390x as it
> is on e.g. x86.

The point is that if the user-callback were to fill in a full ffi_arg,
then ret_buffer would be completely filled.  If ret_buffer isn't fully
written, then that's a bug in the callback PyPy provides to libffi.

> `make` on my laptop (x86) returns without asserting, but
> it does not on s390x. PPC was recently implemented on PyPy and there we
> did also not hit this issue.

Is this on little-endian or big-endian PowerPC?

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU/Linux compilers and toolchain
  Ulrich.Weigand@de.ibm.com