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Filename Latest commit message Latest commit date
Nexoniarz b012060699 zsh: one word in a cross-compile cache, and every $(...) hung 
`X=$(echo hi)` never returned. It has been in docs/history/kernel.md section 7
as "mksh's job control still doesn't reliably progress ... root cause not yet
isolated" with three suspects, and it was none of them, and it was not the
kernel at all.

ports/zsh/Makefile carries a block of `zsh_cv_*` answers for the checks
autoconf cannot run when cross-compiling. One of them was

    zsh_cv_sys_killesrch=no

which reads like a reassuring property and is in fact the answer to the
question configure asks: *does kill(pid, 0) return ESRCH correctly?* `no` makes
configure emit BROKEN_KILL_ESRCH, and Src/zsh_system.h answers that with

    #ifdef BROKEN_KILL_ESRCH
    #undef ESRCH
    #define ESRCH EINVAL
    #endif

zsh's waitforpid() ends its wait on `errno != ESRCH` (Src/jobs.c:1569). With
ESRCH redefined to EINVAL (22) and the kernel correctly returning ESRCH (3),
that condition was true for ever: the shell sat in sigsuspend waiting for a
child it had already reaped. An instrumented zsh says the whole thing in one
line -- kill returned -1, errno is 3, and the constant it is compared against
is 22:

    WFPkill -1 3 22

**Autoconf's own cross-compilation default for that check is `yes`.** Deleting
the line would have been correct. Writing it down as "a fact about SchOS" is
what got it wrong, and the block's comment now says to read each name as the
question rather than as a property.

Verified: `X=$(echo inline)`, `$(/bin/echo external)`, backticks, nested
`$(echo $(echo deep))`, a slow child, and `$(ls /bin | wc -l)` all return.
mksh -- as /bin/sh -- was never affected.

Two corrections to yesterday's note, both confident and both wrong:

  - "Not zsh, mksh hangs the same way" was false. mksh installs as /bin/sh,
    so that test was a `command not found` whose output scrolled past. Had the
    binary been named right, this would have localised to zsh's build in one
    step instead of a day.
  - cmd/sigtest had already proven the kernel's SIGCHLD/sigsuspend contract,
    and a musl-linked probe had already shown kill(pid,0) returning -1 with
    errno == ESRCH == 3 and zsh's own loop condition evaluating false. Both
    results were right; both were read as "so it must be subtler in the
    kernel". What they actually pointed at was the one place the probe and the
    shell differed -- how each was compiled.

The lesson is narrow enough to state: when a probe that reproduces a program's
exact syscall sequence behaves correctly and the program does not, stop looking
under the syscalls and look at the build.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
2026-09-22 00:29:39 +02:00
..
architecture syscall: three globals on the entry path, shared by every CPU 2026-09-21 22:56:45 +02:00
branding branding: one mark, and PSOGM draws it 2026-09-21 21:35:58 +02:00
guides docs: the tree moved and the documentation did not 2026-09-13 20:05:06 +02:00
history zsh: one word in a cross-compile cache, and every $(...) hung 2026-09-22 00:29:39 +02:00
plan zsh: one word in a cross-compile cache, and every $(...) hung 2026-09-22 00:29:39 +02:00
Website branding: one mark, and PSOGM draws it 2026-09-21 21:35:58 +02:00
licensing.md userland: 268 applets, an editor, names that resolve, and a web server 2026-09-14 19:24:55 +02:00
README.md branding: one mark, and PSOGM draws it 2026-09-21 21:35:58 +02:00

README.md

SchOS documentation

Four kinds of document, kept in four directories, because they answer four different questions and go stale at four different rates.
architecture/ What SchOS is Present tense. Describes what is built and working.
plan/ What SchOS will be Future tense. Everything here is unbuilt.
guides/ How to work on it Imperative. Build it, test it, add to it.
history/ Why it is the way it is Past tense. Bugs whose cause is not visible from the fix.

Plus two that belong to no category and apply to everything: licensing.md — read it before copying anyone else's code in — and branding/, which holds the marks and the rules for using them.

The rule that keeps this from rotting

When something is finished, it moves from plan/ to architecture/ and is rewritten as a description of the thing rather than a record of building it.

A completed item is not a ticked checkbox. A ticked checkbox says the work happened; it does not say what the work produced, and six months later the checkbox is the only thing left and it explains nothing.

So finishing a piece of work has three steps, and the third is not optional:

  1. The code works and is tested.
  2. The plan entry is deleted.
  3. A description exists in architecture/ written for somebody who was not there — what it does, what shape it has, what it costs, and what it still does not do.

This is not bookkeeping. The tree has already proved it necessary: the network stack was finished, verified end to end, and for a month afterwards the only description of it anywhere was a checkbox in a roadmap, four levels of indentation deep, written in the past tense of somebody arguing for the work rather than explaining the result.

The "what it does not do" section is the one that pays. Every description in architecture/ ends with one. A document that only lists a subsystem's strengths is marketing, and the reader who most needs the document is the one about to trip over a limitation nobody wrote down.

Start here

New to the tree → architecture/README.md, the system layer by layer, then guides/layout.md for where the files are.

Trying to build it → guides/building.md.

Wondering what happens next → plan/1.0.md, which is the finish line and the register of everything half-built. Then plan/README.md for the order.

About to start something new → the register, first. Nothing new starts while it has rows in it, and a row leaves only by being finished or deleted.

Something is broken and it feels familiar → history/. There is a good chance it is in there.

architecture/ — what SchOS is
README The system, layer by layer. Read first.
boot.md Firmware to the first userspace process.
kernel.md SchIFT: memory, processes, scheduling, traps, signals, SMP.
syscalls.md The call table, and the Linux personality that lets real software run.
filesystem.md The VFS, the buffer cache, procfs, mounts.
schfs.md SchFS: the copy-on-write root filesystem.
devices.md The device model, driver binding, the class vtables.
usb.md xHCI, the USB core, and the class drivers.
graphics.md Framebuffer, text rendering, console, and the crash screen.
terminals.md The six virtual terminals, and how one is switched to.
networking.md Drivers, lwIP, sockets — Unix and INET.
init.md schinit, PID 1 as a role, and the job manifests.

plan/ — what SchOS will be
README The three current decisions and the order they happen in.
1.0.md The finish line, and the freeze. What 1.0 contains, what is deferred, and the register of every half-built thing in the tree.
foundations.md The kernel work everything else is blocked on.
wayland.md The GUI stack, and what gets deleted to make room.
hybrid.md Moving drivers out of the kernel.
schapi.md The long-term API layering, and the compatibility promise.
roadmap.md Everything else still open.

guides/ — how to work on it
building.md Prerequisites and the build, per host.
testing.md The harnesses, and what each one actually proves.
layout.md Repository map, and how to add a program or a port.
adding-a-driver.md Writing one, binding it, publishing its class vtable.

branding/ — the marks
README Shift, the one mark: what it is for, the colour rule, why an icon and a mascot were removed, and why a raster is committed next to its SVG.

history/ — why it is the way it is
README What belongs in here and what does not.
kernel.md Bugs whose cause was nowhere near their symptom.
schfs.md The filesystem's own, from the same period as its design.
moving-to-linux.md The Windows-to-Fedora move, kept for the parts that recur.

Writing one of these

Four conventions, all of them observable in the existing files:

State the cost. Every design choice gave something up. A document that does not say what is a document that will be argued with later by somebody who only sees the downside.

Prefer the measured number to the remembered one. "500 of 3565 files carry the advertising clause" is worth more than "some do", and it was worth the minute it took to count.

Write down the bug that shaped it. Half the non-obvious code in this tree is non-obvious because something failed once. If a design is strange, the strangeness is load-bearing and the reader deserves to know why before changing it.

No dates in headings. A date in a heading turns a description into a changelog, and the description is the thing with a long life. Dates belong in history/, where they mean something.