In current master, the static trampoline code tries to create a temporary file, fill it with trampoline instructions, then map it into the caller's address space. This approach isn't ideal: it mutates external state (in creating the temporary file) and it requires that a file descriptor be free.

Why not instead just generate the trampoline code in the text section of libffi itself, then remap that text section of libffi itself in multiple places? On Linux, you can even perform this remapping without making a file descriptor by using mremap.