[WIP] bpo-31626: Rewrite _PyMem_DebugRawRealloc() by vstinner · Pull Request #3898 · python/cpython

Previously, _PyMem_DebugRawRealloc() expected that the old memory
block remains readable and unchanged after realloc(). This assumption
is wrong on OpenBSD.

Rewrite _PyMem_DebugRawRealloc() as malloc()+free() rather than
realloc(). Debug hooks are reused. The old memory block remains valid
after the new memory block was allocated, so bytes can be safely
copied in a portable way.

The drawback is that _PyMem_DebugRawRealloc() now allocates a new
memory block while the old memory block remains allocated, until the
old memory block is freed, so the peak memory usage can be the double
in the worst case.

The second drawback is that the system realloc() is no more used in
debug mode.