Page "Virtual memory" Paragraph 35

This is not the same as the mechanisms provided by calls such as mmap and Win32's MapViewOfFile, because inter-file pointers do not work when mapping files into semi-arbitrary places.

In Multics, a file ( or a segment from a multi-segment file ) is mapped into a segment in the address space, so files are always mapped at a segment boundary.

A file's linkage section can contain pointers for which an attempt to load the pointer into a register or make an indirect reference through it causes a trap.

The unresolved pointer contains an indication of the name of the segment to which the pointer refers and an offset within the segment ; the handler for the trap maps the segment into the address space, puts the segment number into the pointer, changes the tag field in the pointer so that it no longer causes a trap, and returns to the code where the trap occurred, re-executing the instruction that caused the trap.

This eliminates the need for a linker completely and works when different processes map the same file into different places in their private address spaces.