Commpage is a special memory structure that is always located at the same address in all processes. On macOS, this mapping is provided by the kernel. In case of Darling, this functionality is supplemented by
It is somewhat related to vDSO on Linux, except that vDSO behaves like a real library, while commpage is just a chunk of data.
The commpage is not documented anywhere, meaning it's not an API intended to be used by 3rd party software. It is however used in source code provided on opensource.apple.com. Darling provides a commpage for compatibility reasons.
The address differs between 32-bit and 64-bit systems.
Note that the 32-bit address is outside of permissible user space area on 32-bit Linux kernels. This is why Darling runs only under 64-bit kernels, which don't have this limitation.