Implementation of Linux kernel syscalls

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http://stackoverflow.com – I have read the general answers to these related questions, understanding-the-linux-kernel-source How is the system call in Linux implemented? How does a syscall actually happen on linux? but still left with questions of my own. For example, on int 0x80 the kernel services the system call, but what does it mean to "service" a call? e.g. if a service call is made for getuid #define __NR_getuid (__NR_SYSCALL_BASE+ 24) then once int 0x80 occurs, the kernel services the call. So what exactly must the kernel do to implement getuid? Somewhere there must be some code which (HowTos)