pdp11-ld

The link editor — the authentic 2.9BSD ld.c on an LP64 host. Links classic 2BSD a.out objects and archives into 0407/0410/0411 executables and 0430 auto-overlay images.

pdp11-ld [-o a.out] [-X|-x] [-r] [-s] [-n] [-i] [-d] [-t]
         [-Z ovl.o ... -Z ... -L] [-u sym] [-e entry] files... [-lx]

• Overlays are not an afterthought. The MENLO overlay machinery is unconditional in the 2.9 source (-Z brackets overlay segments, -L ends them, NOVL=7), and the roundov() LP64 infinite-loop fix here is what makes overlay links terminate. Proven by linking the GENERIC 2.9 kernel: unix comes out byte-identical to the native link.
• Era libraries without flags. -lx resolves against ../lib/<universe>/libx.a relative to the binary ($PDP11_UNIVERSE, default bsd29), falling back to a flat ../lib.
• Middle-endian faithful. Archive dates/sizes and __.SYMDEF offsets pass through the PDPL() PDP-11 long swap, so what ld reads is exactly what native tools wrote.

Documentation

• Design — the two-pass link model, segment and overlay layout, and relocation resolution.
• User guide — options, overlay control, library search, and examples.
• docs/porting.md — the 16-bit-I/O porting story (every on-disk word pinned to uint16_t).

Build and test

make          # builds ../../bin/pdp11-ld
make check    # covered by tests/ld/*.sh at the repo root and the
              # ld-sweep / kernel-link oracles (213 clean links, 0
              # differ; byte-identical overlay kernel)