[DISPATCH-2270] Do not rely on long type being large enough to transfer C pointer values from C to Python

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.17.0
• Fix Version/s: 1.19.0
• Assignee: Jiri Daněk
• Reporter: Jiri Daněk
• Created: 31/Oct/21 09:26
• Updated: 22/Mar/22 19:12
• Resolved: 31/Jan/22 11:14

Description

// We pass pointers as longs via the python interface, make sure this is safe.
STATIC_ASSERT(sizeof(long) >= sizeof(void*), pointer_is_bigger_than_long);

This is wrong on Win64, where long is 4 bytes. There is multiple possible solutions:

1. use long long, trivial workaround
   • https://docs.python.org/3/c-api/arg.html#c.Py_BuildValue
2. construct the python value explicitly, probably the nicest solution, and should not even add extra overhead
   • https://docs.python.org/3/c-api/long.html#c.PyLong_FromVoidPtr
3. use PyCapsules, not a good fit for existing code, requires changing signature in C on the callee side
   • https://docs.python.org/3/c-api/capsule.html
   • https://docs.python.org/3/extending/extending.html?highlight=capsule#providing-a-c-api-for-an-extension-module

and maybe even more possibilities. I am inclined to go with the PyLong_FromVoidPtr value constructor.