Editing Position-independent code (section)

== Multics ==
In [[Multics]] each procedure conceptually{{efn|name="NB_REASON"}} has a code segment and a linkage segment.<ref>{{cite book
 | title       = The Multics system; an examination of its structure
 | first       = Elliott Irving
 | last        = Organick
 | author-link = Elliott Organick
 | year        = 1972
 | isbn        = 9780262150125
 | lccn        = 78157477
 | publisher   = [[MIT Press]]
 }}
</ref>
<ref>{{cite journal
 | journal     = [[Communications of the ACM]]
 | volume      = 11
 | number      = 5
 | title       = Virtual Memory, Processes, and Sharing in Multics
 | first1      = Robert C.
 | last1       = Daley
 | first2      = Jack B
 | last2       = Dennis
 | authorlink2 = Jack B. Dennis
 | pages       = 306–312
 | date        = May 1968
 | publisher   = [[Association for Computing Machinery]]
 | doi = 10.1145/363095.363139
 | url         = https://multicians.org/daley-dennis.html
 | access-date = July 21, 2024
 }}
</ref> The code segment contains only code and the linkage section serves as a template for a new linkage segment. Pointer register 4 (PR4) points to the linkage segment of the procedure. A call to a procedure saves PR4 in the stack before loading it with a pointer to the callee's linkage segment. The procedure call uses an indirect pointer pair<ref name="Honeywell_1982"/> with a flag to cause a trap on the first call so that the dynamic linkage mechanism can add the new procedure and its linkage segment to the Known Segment Table (KST), construct a new linkage segment, put their segment numbers in the caller's linkage section and reset the flag in the indirect pointer pair.