Look at the files in glibc:

sysdeps/unix/sysv/linux/read.c
sysdeps/unix/sysdep.h
sysdeps/unix/sysv/linux/include/sys/syscall.h
sysdeps/unix/sysv/linux/x86_64/64/arch-syscall.h
sysdeps/unix/syscalls.list

Use arch-syscall.h to show the system call numbers for the x86_64 architecture.

And look at 
bionic/arch/x86/entry/entry_64.S
bionic/arch/x86/entry/syscalls/syscall_64.tbl
bionic/include/linux/syscalls.h