Day 22 evidence

Date: 2026-09-19

Source baseline

  • Base commit: 346525f3a5c1924da6c01f87ff168ee3bc1511cf
  • Kernel image SHA-256 after the final source assertion change: 44fa4a4324acc22ef69b8e185e672c3238bf0744b210cd645d4994fcb455d959
  • Disk image SHA-256: 15349fd7449d2260e3df91c93127b3f320fa3f27e6b0e75423cf4e2653fa5573
  • Day 22 user ELF SHA-256: 0fe8e6739c5c5ad32fc3a88e923ef3e6b17cf3ab37ad04b2c799e99f372d0b01

The final attachment hash and standalone rebuild result are added after packaging. The Git commit containing this file is intentionally not self-referenced; use git log -- <path> to recover it.

Environment

  • QEMU 8.2.2 (Debian 1:8.2.2+ds-0ubuntu1.18)
  • SeaBIOS 1.16.3 package image
  • GDB 15.1
  • GCC 13.3.0
  • GNU Binutils 2.42
  • NASM 2.16.01
  • Machine: pc-i440fx-7.2, TCG, qemu32, 1 CPU, 64 MiB

The unpacked QEMU/GDB binaries live under /tmp/build-an-os-tools and are not delivery artifacts.

Command

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PATH=/tmp/build-an-os-tools/bin:$PATH \
LD_LIBRARY_PATH=/tmp/build-an-os-tools/root2/lib/x86_64-linux-gnu:\
/tmp/build-an-os-tools/root2/usr/lib/x86_64-linux-gnu \
QEMU_MODULE_DIR=/tmp/build-an-os-tools/root2/usr/lib/x86_64-linux-gnu/qemu \
make check-fd \
  QEMU=/tmp/build-an-os-tools/bin/qemu-system-i386 \
  GDB=/tmp/build-an-os-tools/bin/gdb-multiarch \
  BIOS=/tmp/build-an-os-tools/root2/usr/share/seabios/bios-256k.bin \
  QEMU_DATA=/tmp/build-an-os-tools/root2/usr/share/qemu

Exit status: 0.

Normal run

day22-fd-gdb.txt records both checkpoints:

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PASS: faulting child closed every fd before ZOMBIE publication
PASS: independent/shared offsets, short EOF, limits, rollback, exit cleanup and page recovery verified

Final values checked by GDB:

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fd_passed=1
fd_terminal_mode=0
fd_root_status=22
fd_reaped=5
fd_exit_closes=14
fd_exit_tasks=5
fd_pointer_faults=5
file_peak_live=7
file_allocations=file_releases=16
free_pages=fd_initial_pages

The guest checks two independent opens, a shared parent/child offset, a page-faulting child, EOF and short reads, zero length, read/write permissions, fd reuse, fd/open-file table exhaustion, and five rejected user-buffer ranges. The full-file FNV-1a is f34dc752 for 1479 bytes.

Injected failure run

day22-fd-fail-gdb.txt records:

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PASS: six ELF allocation failures plus kernel-stack failure rolled back mapped refs, then recovered

The image observes fd_spawn_rollbacks=7, then performs a successful spawn/read/wait. File allocation/release and free-page counts return to their baselines.

Terminal run

day22-fd-terminal-blocked.txt observes the reader in BLOCKED, with trap_depth=1 and waiting_on=&keyboard_waiters. day22-fd-terminal-idle.txt observes a later PIT tick, no extra block attempt, idle HLT=1, and IF set. QEMU HMP then sends a, b, and Return through the emulated PS/2 controller.

day22-fd-terminal-done.txt records:

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PASS: terminal reader blocked in trap depth 1, idle PIT advanced, HMP keys produced ab\n

The user process performs three one-byte reads and reports D22 TERMINAL read ab\n one byte at a time. This validates the QEMU i8042 path, not a physical keyboard, canonical terminal mode, Ctrl-D, or multiple readers.

Boundaries

  • FAT corruption and non-contiguous chains are dynamically covered by Day 21 check-fat; Day 22 does not rerun a corrupt volume through the fd syscall layer.
  • The implementation is single-CPU and relies on syscall trap depth plus preemption suppression to serialize the non-reentrant FAT workspace and shared offsets.
  • Directory descriptors, seek, writable files, canonical terminal input, Ctrl-D, close-driven terminal EOF, SMP, and concurrent close-vs-read are not implemented.

Cumulative regression

The cumulative run in day22-cumulative.txt records successful exits for:

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PASS check-fat
PASS check-block
PASS check-process
PASS check-syscall
PASS check-elf
PASS check-memory
PASS check-runtime-limit
PASS check-keyboard

These are real QEMU/GDB checks, not build-only targets. check-fat includes the non-contiguous chain and eleven corrupt-volume images; check-block includes timeout, missing DRQ, and device ERR; check-runtime-limit boots the exact 128 KiB file and 256 KiB runtime boundaries.

Standalone attachment verification

os-day-22.zip SHA-256 is 068c86aa51a33813a837e4a91ab2646a9db72209825bd1d221563a21c787b8a0. The archive contains no build/ directory. It was extracted into a new mktemp directory and rebuilt from scratch before running check-fd, check-fat, check-block, check-process, check-syscall, check-elf, check-memory, check-runtime-limit, and check-keyboard; every target exited 0.

The rebuilt kernel.bin, mbr.img, and day22-user.elf hashes match the source workspace values above and all three files pass byte-for-byte cmp. Full output is saved as docs/day22-zipcheck.txt. This log verifies the already frozen ZIP, so it is intentionally kept outside the archive itself.