pdp11-c1 — user guide

pdp11-c1 is the code generator of Ritchie's PDP-11 C compiler — the second pass. It reads the intermediate form pdp11-c0 produced and writes PDP-11 assembler text for pdp11-as. It is not a command you run directly: it is a compiler pass, driven by pdp11-cc, with a fixed three-argument calling convention and temp files cc creates and cleans up. This guide documents that convention so you can recognise it in cc -v output or drive it by hand when debugging.

For how it works inside — the code table, the table build pipeline, the soft floating point — see the design document.

1. Synopsis

pdp11-c1 intfile strfile out.s [-V]

intfile — c0's first temp file, the intermediate expression/statement stream (read as stdin);
strfile — c0's second temp file, the strings and initialised data, appended in .data; pass "-" to skip it;
out.s — the assembler output (written as stdout);
-V — enable Menlo overlay mode (only in a MENLO_OVLY build); cc passes it when overlays are requested.

All three positional arguments are required — c1 exits with Arg count if fewer are given. It reads no environment and no other options.

2. What it emits

Assembler text for pdp11-as: .text/.data/.bss segments, .globl directives, function labels with the jsr r5,csv / jmp cret prologue and epilogue, and the instruction stream chosen by the code table. Integer constants are printed in octal (the 2BSD as convention), so return 42 emits mov $52,r0. Floating-point constants are emitted as DEC F/D-format .data words computed by the soft floating point (see design §5), and any FP use emits a .globl fltused reference.

3. Invocation (via cc)

cc runs c1 as the c1 stage of cpp → c0 → c1 [→ c2 with -O] → as → ld. It is invoked as

c1 tmp1 tmp2 tmp3          # or  c1 tmp1 tmp2 tmp5   under -O

where tmp1/tmp2 are c0's two temp files and the third argument is the assembler source: tmp3 normally, or tmp5 under -O so that pdp11-c2 can rewrite it into tmp3 afterwards. cc -S names the output file.s and stops after this pass. You do not choose these paths; cc allocates and removes them. cc -v prints Pass 1 when it reaches c1.

4. Exit status

0 — success (assembly written).
non-zero — one or more errors were emitted (nerror != 0): a missing temp file, an unwritable output, a malformed intermediate stream, an illegal operation, or register/table exhaustion. Each error is printed to stderr as <line>: <message>.

cc treats a non-zero c1 status as a failed compile for that file and moves on.

5. Examples

Normally you never type c1; you drive the pipeline through cc:

pdp11-cc -S prog.c            # stop after c1: leaves prog.s
pdp11-cc -O -S prog.c         # same, but c2-optimised assembly
pdp11-cc -v -c prog.c         # see each pass, including "Pass 1" (c1)

To run the pass by hand for debugging (reproducing what cc does between the temp files):

pdp11-cpp prog.c > prog.i
pdp11-c0  prog.i t1 t2        # c0 writes its two temp files
pdp11-c1  t1 t2 prog.s        # c1: intermediate + strings -> assembly
pdp11-c1  t1 -  prog.s        # skip the string/data file

Continue to the design document for the code-table interpreter and how table.s becomes compiled-in C.