SDL 3 has no OSS backend and SchOS has no ALSA kernel side, so sound now
goes SDL -> alsa-lib -> alsa-plugins' OSS plugin -> /dev/dsp. That path
found two bugs underneath it:
- ac97: resetting the PCM-out box also clears the descriptor list address,
and nothing set it again. Every stream after the first stop played a
"list" at physical address 0 -- silence -- and ALSA resets before each
stream. If the engine halts at the end of the queue, the run bit is set
again.
- /dev/dsp: SETFRAGMENT, GETFMTS, GETCAPS, SETTRIGGER, GETOPTR and GETODELAY
for the plugin's ring-and-pointer model, and poll(), writable once a whole
fragment fits (ALSA spun at 76% CPU otherwise). speaker-test now plays in
real time at 0% CPU, verified in a recording of QEMU's AC'97.
- /etc/asound.conf: the default device is a plug to the OSS device at 16-bit
stereo 48 kHz, what every SchOS audio driver plays.
Also:
- getstackpcs: each frame link must go up the same stack by less than
KSTACKSIZE. The chain ends at the syscall entry with the user's rbp,
which lbreakouthd uses as a register (-1024); the walk dereferenced it
under the syscall tracer and the kernel panicked inside acquire().
- fb: FBIOGET_VSCREENINFO reports nominal timings, as Linux's efifb does,
instead of zeros, which Xorg's fbdev turned into a 0 Hz RandR mode.
- procdump (Ctrl-P) shows where runnable threads are in user space.
- World: lbreakouthd instead of lbreakout2 (its stk.c passes vsnprintf a
size of 511 plus the prefix length, and Alpine's fortified headers trap on
that), plus curl, alsa-lib and alsa-plugins.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
Sixty-five headers sat side by side in include/, so `#include "irq.h"`
said nothing about where irq.h was or what it belonged to, and errno.h,
stat.h and fcntl.h at the top shadowed the system's for any host tool
built with -I./include. They are in folders now -- arch/ core/ fs/
dev/ gfx/ net/ uapi/ (and ldls/ for the Linux driver layer) -- and
every include names the folder, as Linux's do: "core/proc.h".
Done mechanically and checked the hard way: the kernel built from this
tree disassembles identically to the one built from the tree before
it. The full image boots, and userland is the same set of programs.
Paths in docs and comments follow; docs/guides/layout.md has a table
of what is where, and tools/fix-includes.py rewrites old-style
includes from the folders in the tree, for code written before this.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
Neither is Fedora-specific. A different host and a freshly built
userland simply drove code that Windows never reached.
tools/mkfs.c did not compile at all. The DT_UNKNOWN/DT_DIR/DT_REG
fallbacks sat above <dirent.h>, so on glibc -- which spells them as
enumerators -- the #ifndef asked before the header was read, always
answered "missing", and then the header's own enum expanded to
`enum { 0 = 0, ... }`. Move the fallbacks below the include. The
include cannot move up instead: it has to follow the #undef that ends
the `#define dirent schfs_dirent` block.
getstackpcs() page-faulted. It dereferenced rbp[1] without validating
rbp, and the guard rejected 0xffffffff -- dead code on x86-64, already
caught by the KERNBASE test -- while the value that actually turns up
is all-ones, which is above KERNBASE. rbp[1] then wrapped to 0x7 and
took trap 14. `cp` panicked the kernel every time. Bound rbp from
above and require 8-byte alignment.
That second one masks other bugs: getcallerpcs() runs on every lock
acquisition and again from the trap handler, so a walker that can
fault replaces a real diagnosis with a bogus one.
Baseline on the Fedora laptop is now green: make ports, make,
make schfs-check including the round-trip that had never run, and
bootcheck at 27/27 plus 108 [ok] across the extended suites.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.
No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.
