pdp11-xdevalpha

Documentation

pdp11-das — user guide

pdp11-das is the PDP-11 disassembler — the inverse of as. It reads a PDP-11 object, linked executable, or archive from any era (First Edition 1971 through V7 and 1/2.8/2.9/2.10/2.11BSD) and prints the instructions back,…

pdp11-das — user guide

pdp11-das is the PDP-11 disassembler — the inverse of as. It reads a PDP-11 object, linked executable, or archive from any era (First Edition 1971 through V7 and 1/2.8/2.9/2.10/2.11BSD) and prints the instructions back, labelling functions, data, and branch/call targets from the symbol table. It decodes through the same opcode table the assembler encodes from, so the two agree on the whole instruction set. It runs on your host.

For the input shapes, the two era symbol-table formats, the code/data walk, and the round-trip property, see the design document; for the byte-level reassembly rules, the field guide.

1. Synopsis

pdp11-das [-a] [-p] [-s] [-6] [-2] [-y] [-J]
          [--sys=...] [--isa=...] [--std=...] file

file is a bare object (.o), a linked a.out, or an archive (.a). The format is auto-detected from its first word — a First-Edition 0405 executable, a 0407/0410/0411 a.out, or an archive (0177545); the era dialects below are the only things chosen by option.

Options

option meaning
(none) a listing: address, bytes, and disassembly, with symbols as labels
-a emit reassemblable as source — as turns it back into the object
-p write every listing to stdout (instead of per-object .dis files)
-s content-only: drop the symbol table of a relocation-stripped image (all-numeric)
-6 V5/V6 syscall personality (sys/trap inline-argument counts)
-2 1972 syscall personality, plus the V1-era .. load bias (040000)
-y accepted as a no-op (its behavior is now the default)
-J decode late J11 hardware (MFPT, SPL, CSM, TSTSET/WRTLCK, FIS, MED/XFC, CIS)
--sys= syscall axis alone: none, v1, v6, bsd211
--isa= instruction set: v1, v4, bsd211, extended (extended = -J)
--std= era dialect(s), comma-separated: v1..v7, bsd, newbsd, extended

By default, das keeps the symbol table of a relocation-stripped image (a kernel or unstripped executable) and labels from it; -s reverts to the older all-numeric mode. --std is a convenience that sets the syscall and ISA axes together for a named era; the object format is always detected from the file, never from a flag.

Output

By default a single listing — a bare object, or an a.out with no per-object boundaries — goes to stdout. When there are several listings to separate, each is written to its own <stem>.<object>.dis file:

  • a linked a.out is split back into per-object listings by the N_FN file-name symbols the linker left behind (<stem>.crt0.o.dis, <stem>.main.o.dis, …); its data and bss, which cannot be attributed to an object, go together to <stem>.DATA.dis;
  • an archive disassembles each member to <stem>.<member>.dis.

-p overrides that and sends everything to stdout instead. Each output opens with a banner naming the tool and the object; a listing also prints the magic and segment sizes, and the banner flags any reassembly caveat it detected (as -n for a 2.11 string-table symtab, as -V for an overlay-assembler object, as --isa=bsd211 for a PC-relative MMU operand).

In -a mode the output is clean as source — / comments, .globl declarations, synthetic .L<addr> labels for un-named targets — with no address/byte columns, so as can read it straight back.

The round-trip

das -a produces assembly that as reassembles into the same object, byte for byte across the text and data segments — the disassembler is a faithful inverse, proven over the whole multi-era corpus. This is useful for inspecting, patching, and rebuilding an object you only have in binary form.

pdp11-das -a foo.o > foo.s        # recover reassemblable source
pdp11-as -o foo2.o foo.s          # foo2.o's text+data is byte-identical to foo.o

Exit status

Zero on success. Non-zero on a usage error (an unknown option or a missing file argument), a file it cannot open or fully read, or input whose first word is not a recognized PDP-11 object, executable, or archive magic.

Examples

pdp11-das foo.o                   # a listing to stdout
pdp11-das -a foo.o > foo.s        # reassemblable source
pdp11-das -p prog                 # a linked a.out, all objects to stdout
pdp11-das prog                    # split into prog.<object>.dis + prog.DATA.dis
pdp11-das libc.a                  # each member to libc.a.<member>.dis
pdp11-das -2 --sys=v1 v1.out      # First-Edition personality: 1972 syscalls, .. bias
pdp11-das -J --isa=bsd211 kern    # decode the late J11 hardware instructions
pdp11-das -s vmunix               # a stripped kernel, all-numeric content

Continue to the design document for the input shapes, the two symbol-table formats, the recursive-descent code/data walk, and the round-trip guarantee.