Search notes:

arch/x86/include/asm/syscall.h

Access to user system call parameters and results (See asm-generic/syscall.h for description of what we must do here).

sys_call_ptr_t

sys_call_ptr_t is a syscall function pointer:

typedef long (*sys_call_ptr_t)(const struct pt_regs *);

sys_call_table is an array of sys_call_ptr_t.

sys_call_table is populated in arch/x86/um/sys_call_table_64.c and/or arch/x86/entry/syscall_64.c.

The function corresponding to a sys call number is looked up in the array and called in do_syscall_x64().