How can I create a function call in GIMPLE representation?

I'am trying to create a function call in Gimple.
Since the documentation on this is so poor, I can't see how to proceed.
In particular I would like to know how to build this function:

uint32_t *m_addr = mmap(0,8, PROT_READ | PROT_WRITE , MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

I looked everywhere but I couldn't find anything clear.
I would also be grateful if you had some advice on where to study this subject. Because gcc's documentation is really poor