3 The source listing is preceded by a cross-reference that lists every defined
4 constant, struct, global variable, and function in xv6. Each entry gives,
5 on the same line as the name, the line number (or, in a few cases, numbers)
6 where the name is defined. Successive lines in an entry list the line
7 numbers where the name is used. For example, this entry:
10 0374 2428 2466 2657 2658
12 indicates that swtch is defined on line 2658 and is mentioned on five lines
13 on sheets 03, 24, and 26.