What is the posix_memalign() equivalent for the PostgreSQL?

I am developing an extension for the PostgreSQL that write/read some external files from the PostgreSQL. In order to write/read, I am using the O_DIRECT flag and using the posix_memalign to allocate memory. I would like to know if the postgresql internal library provides an equivalent function for the posix_memalign since I am getting unexpected errors. All my allocations are in the TopMemoryContext since I am working with several buffers that must be alive while the PostgreSQL Server is activated.