Search notes:

include/uapi/asm-generic/unistd.h

include/uapi/asm-generic/unistd.h contains the system call numbers, based on the layout of the x86-64 architecture, which embeds the pointer to the syscall in the table: 
#define __NR_io_setup     0
#define __NR_io_destroy   1
#define __NR_io_submit    2
…
#define __NR_cachestat  451
The macro __NR_syscalls keeps the number of syscalls: 
#define __NR_syscalls   452

See also

The syscall function prototypes are defined in include/linux/syscalls.h.

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