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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
..
1.0.md zsh: one word in a cross-compile cache, and every $(...) hung 2026-09-22 00:29:39 +02:00
foundations.md sockets: a descriptor can cross between processes 2026-09-13 19:49:37 +02:00
hybrid.md hybrid: H4 withdrawn -- USB is not a peripheral 2026-09-14 01:45:58 +02:00
README.md debugger: D5, the network transport -- and the plan closes 2026-09-14 15:33:53 +02:00
roadmap.md docs: the tree moved and the documentation did not 2026-09-13 20:05:06 +02:00
schapi.md freeze: one register for everything half-built, and the corners cleared 2026-09-13 20:28:05 +02:00
wayland.md freeze: one register for everything half-built, and the corners cleared 2026-09-13 20:28:05 +02:00

README.md

What happens next

Everything in this directory is unbuilt. When a piece of it is finished it leaves — deleted from here, rewritten as a description in ../architecture/. See the rule.

Read 1.0.md first.

It draws a finish line and puts most of the work below on the far side of it. Anything not named there is not being worked on, and the documents in this directory describe more than 1.0 contains.

It also holds the register of unfinished work, which is the one place anything half-built is listed. No new capability starts until that register is empty, and a row leaves it only by being finished or by being deleted from the tree.

The three current decisions

Taken together, because they turn out to need the same foundation.
wayland.md The GUI stack becomes Wayland. SchWM and SchDE are deleted — actually gone from the tree, not marked; Schcom survives and changes its wire format.
hybrid.md Built. All four mechanisms exist, the GPU driver runs outside the kernel, it survives being killed, and the display mode can be changed from a process. H4 (USB) was withdrawn rather than left open — USB is the bus peripherals arrive on, not a peripheral.
init.md Built. PID 1 is now a role the kernel refills; the description moved to ../architecture/init.md.

And the one they all wait on:
foundations.md Descriptor passing, shared memory, sockets in the filesystem. The critical path. Item 1 is built — sendmsg/recvmsg with SCM_RIGHTS.

And the one that says which parts of the above are actually being worked on:
1.0.md The finish line. Four gates, and everything else explicitly deferred.

And the one the hybrid mechanisms were built for:
ldls.md Built. The Linux Driver Layer for SchOS: someone else's drivers, in a process, reached through /dev/pci. ping works over 8139too and over e1000. The description moved to ../architecture/ldls.md.
debugger.md Built, all of it, including the network transport. A debugger that observes rather than halts and answers in this kernel's own vocabulary: symbols, a log that outlives the kernel, /dev/dbg, whose, hardware watchpoints, and schdbgd. The description moved to ../architecture/debugging.md.

Two longer-horizon documents sit behind these: schapi.md, the API layering and the compatibility promise, and roadmap.md, which holds everything still open that is not one of the three above.

The order

Set by 1.0.md, which is the authority. In short:

0. Fix what is already wrong — first

Not a document of its own; it is Gate 0 of 1.0.md, assembled from the What it does not do sections in ../architecture/.

Before any new capability, and the reason is the one that put netdev_selftest() before the TCP/IP stack: a compositor built on a kernel with an unexplained hang and a socket layer that reports success for things it did not do will fail in ways indistinguishable from its own bugs.

1. foundations.md — the critical path

Both the Wayland work and the hybrid work stop here. Descriptor passing and shared memory are the substrate for handing a buffer to a compositor and for handing a device to a driver process. Doing it once for both is the entire reason these are one plan rather than three.

2. init.md — before the desktop, not after — done

A compositor being brought up for the first time crashes constantly, and something that restarts it and says why is worth far more during that work than at the end of it. Built; see ../architecture/init.md.

3. hybrid.md — moved up, and the reason is worth recording

This document used to put the hybrid work after 1.0, deliberately last, on this argument:

designing a userspace driver interface with no driver consuming it produces an interface that is wrong in ways nobody can see

The argument was sound and the conclusion drawn from it was wrong. What forced the change was the driver situation: SchOS cannot write a driver for every device that exists, no project can, and the only route to the hardware support an established OS has is a compatibility layer with the foreign drivers kept outside the kernel. That layer is this plan's mechanisms. It is not optional and it is not late work.

The original argument still holds, and it is answered rather than ignored: SchOS's own drivers are the consumers. vgpud is a real driver, with real requirements, and building the interface against it is what keeps it a general mechanism rather than a hole shaped like something foreign. The compositor is still a demanding consumer — it is no longer the only one available.

Four mechanisms, all built. One eviction done, the second withdrawn with its reasons recorded, and the foreign driver host they were for is ../architecture/ldls.md — built, and carrying packets.

4. wayland.md — with the GPU driver either side of the seam

W1–W3 and a terminal. W4 and W5 are post-1.0. Item 1 of foundations.md — descriptor passing — was the thing it could not start without, and it now exists.

In one sentence

Fix what is broken, build the descriptor-passing and shared-memory substrate, make init survivable, move the drivers out through an interface SchOS's own drivers have to live with first — and put a terminal on the screen.

What this plan does not address

Stated here so it is not mistaken for covered:

  • No IOMMU, so the hybrid work isolates against bugs and not against a hostile driver.
  • No page cache, so foundations.md delivers a memfd and not a general answer to shared file mappings. The general answer is still owed.
  • No garbage collector for descriptors in flight, so an AF_UNIX socket passed over itself and never received leaks. Bounded at thirty-two sockets, and nothing on this plan does it.
  • No dynamic linking, so no Mesa, no accelerated clients, and no third party shipping a .so for anything.
  • A new compatibility surface between PID 1 and PID 2, created by a plan whose own schapi.md §3 spends a section warning about those.
  • The three open networking items — getsockname, routing, and interrupt-driven receive — are untouched by any of this and still open. They are in roadmap.md.