[Python-Dev] Update on PEP 523 and adding a co_extra field to code objects (original) (raw)

Christian Heimes christian at python.org
Tue Aug 30 06:28:11 EDT 2016

On 2016-08-30 01:14, Brett Cannon wrote:

So the struct in question can be found at https://github.com/python/cpython/blob/2d264235f6e066611b412f7c2e1603866e0f7f1b/Include/code.h#L10 . The official docs say the fields can be changed at any time, so re-arranging them shouldn't break any ABI compatibility promises: https://docs.python.org/3/c-api/code.html#c.PyCodeObject . Would grouping all the fields of the same type together, sorting them by individual field size (i.e. PyObject*, void*, int, unsigned char*), and then adding the coextra field at the end of the grouping of PyObject * fields do what you're suggesting?

You don't have to resort them all, just move co_firstlineno after co_flags, so all int fields are together. Pointers are typically alignment to multiple of 64 on a 64bit machine. In its current shape PyCodeObject is padded with two unused areas of 32bit: 5 * int32 + 32 bits of padding, 9 * pointers (64 bits each), 1 * int32 + another 32 bits of padding, 3 * pointers. When you move co_firstlineno, you fill in the gap.

Christian

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