Blog publication task for PR #1250

Source: #1250
Merged commit: e7919fdc91bd9ff4aa7ab91dd2a6dd4218176357

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The TRI-27 emulator stops lying about its own container

DRAFT — Merged PR; unpublished blog draft

PR: #1250

Head SHA: 6a9d1ac8dee8c876edd906612f1e1d70e49aaad0

This file is an unpublished artifact, not an instruction to an agent.

Merged PR; unpublished blog draft. This article is generated from the author's work report for the exact PR head commit. Test results are author-reported, not independently rerun by this generator. Merge status is not proof of deployment or runtime correctness.

Work report

The six pinned TRI-27 emulator defects from the S05 findings are fixed: CALL pushes the next address, the loader and the fetch agree on one four-byte word per fetch unit at byte 12, the writer and loader share the twelve-byte header, the CONSTANTS parser reads id then count then count*8 bytes, the modulus labels say 3^9, and the SACR mode round-trips through the decoder.

What changed

• executor.zig: CALL pushes pc + 1, so RET resumes after the call site (issue 1165).
• loader.zig: the CODE payload is repacked one word per four-byte fetch unit at byte 12 + i*4 and pc is set to 3, so a program executes with no padding NOPs and jump targets line up (issue 1166).
• loader.zig: the loader skips the two padding bytes the writer emits, so a container written by tri_asm.zig loads at the addresses its labels count from (issue 1167).
• loader.zig: the CONSTANTS parser reads the section id, then the count, then count * 8 bytes as documented (issue 1168).
• tri_cpu.zig: the modulus comments label 19683 as 3^9 instead of 3^27 (issue 1169).
• decoder.zig: SACR is an immediate instruction in both decode and encode, so its mode field is read and written (issue 1170).
• tri_emu_main.zig: instruction count and code size count from the twelve-byte header.
• specs/tbin_format.md: the container documentation restates the canonical twelve-byte header and the constants layout.

Context and reasoning

Where the six defects came from: the S05 specs of the pinned TRI-27 emulator recorded them as findings, and each sub-issue quotes the spec, the code at the pin and a conformance vector that reproduces the failure.

Why CALL looped forever: the executor pushed the address of the CALL itself, so RET returned to the call site and every CALL/RET pair spun until the instruction budget; the fix pushes pc + 1 and a regression test drives a full call and return.

One code word per fetch unit: the loader wrote eight-byte memory words while run fetches four-byte units at pc * 4, so programs executed padding NOPs; the loader now repacks the payload at byte 12 + i*4 and pc starts at 3.

The two-byte header disagreement: tri_asm.zig pads its header to twelve bytes while the loader read the code from byte ten; the loader now skips the same padding, so a written container loads at the addresses its labels count from.

The remaining three fixes: the CONSTANTS parser reads the id, then the count, then count * 8 bytes; the modulus labels say 3^9 instead of 3^27; and the SACR mode is an immediate the decoder reads, so every sacred operation mode round-trips.

Reported verification

• [passed] Command: zig test src/tri27/emu/loader.zig. Result: All 2 tests passed, including container placement and CONSTANTS parsing.. Evidence: zig 0.16.0 on aarch64-macos; the two new regression tests in loader.zig.
• [passed] Command: zig test src/tri27/emu/executor.zig -lc. Result: All 16 tests passed, including CALL/RET resumption.. Evidence: zig 0.16.0 in a scratch copy with the three host-file handlers stubbed (unrelated to the change; the host's zig 0.15.2 cannot link libSystem on macOS 26).
• [passed] Command: zig test src/tri27/emu/decoder.zig -lc. Result: All 7 tests passed, including the SACR round-trip in every mode.. Evidence: zig 0.16.0 with a scratch shim for std.meta.intToEnum, which 0.16 removed; the repository CI pins zig 0.15.2.
• [passed] Command: zig test -fno-emit-bin for loader, decoder, executor, tri_asm, tri_cpu, tri_emu_main. Result: Semantic analysis passed for all six files.. Evidence: zig 0.15.2, the version the repository CI uses.

Limits and open questions

• The emulator tests do not run in this repository's CI; the change is compile-verified there through the tri executable and behavior-verified on a host that can link tests.
• The S05 specs in gHashTag/t27 (specs/isa/tri27_machine.t27, tri27_bytecode.t27, ternary_encoding.t27), the Python model in tools/trinity_tri27.py and the conformance vectors still describe the pinned pre-fix behavior and need a matching follow-up pull request in gHashTag/t27.
• The CALL stack guard and the sp word/byte semantics were left as pinned; they are outside the six issues.

Receipts

• gHashTag/trinity PR #1250
• Reported head commit 6a9d1ac8dee8
• Merge commit e7919fdc91bd

Topic tags

#tri27 #emulator #loader #bugfix