Commits on Apr 17, 2019

1. Fix 64-bit Windows compatibility …

   Py_BuildValue() expects Py_ssize_t values for buffer lengths provided
   for "y#" and similar format specifiers. The PUBLICKEYBYTES and
   SECRETKEYBYTES constants passed to Py_BuildValue() in
   ed25519_publickey() are treated as 32-bit int values by default, so they
   must be cast to Py_ssize_t to work correctly on 64-bit architectures, as
   Py_ssize_t is 64 bits on such targets.
   
   For x86-64 targets, this was only causing issues on Windows, as the
   Microsoft x64 calling convention only uses four registers for argument
   passing instead of the six used by the System V AMD64 ABI (Linux, macOS,
   etc.). 32-bit values are automatically zero-extended to 64-bits when
   loaded into a register, so the size arguments get promoted to 64-bits
   automatically if they can be passed in a register. The SECRETKEYBYTES
   argument, being the fifth argument to Py_BuildValue(), gets passed on
   the stack on Windows, so the upper 32-bits of the value read for that
   argument are pulled from whatever is in memory adjacent to the value in
   the stack, often leading to a MemoryError being raised as
   Py_BuildValue() attempts to allocate a large amount of memory for the
   "signkey" bytes object.

   

   okready committed Apr 17, 2019
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