title: Is malloc/free a syscall or a library routine provided by libc?
body: <p>If malloc/free is implemented as a library routine in libc, then is it implemented on top of the <em>sbrk</em> syscall or the <em>mmap</em> syscall, or something else?</p>
  
  <p>And to be general, does the function declared in <em>sys/syscall.h</em> contains ALL the system calls in the target machine?</p>