Port library/modules/std/sched.sx to run on aarch64-linux alongside
aarch64-macOS, validated byte-identical on both via Apple `container`.
Per-OS bits are comptime-branched:
- MAP_AP (mmap MAP_ANON flag): linux 0x22 / macOS 0x1002.
- fd-readiness backend: epoll on linux, kqueue on darwin (epoll import
scoped to the linux branch). block_on_fd, the run-loop Mode-2 drain,
and cancel_io_waiter_for each branch; the epoll paths EPOLL_CTL_DEL on
fire and on early-wake (EPOLLONESHOT only disables a registration;
kqueue EV_ONESHOT auto-removes it).
- first-entry trampoline: a per-OS hand-written global-asm symbol becomes
a naked sx fn fib_tramp (mov x0,x19; br x20) + register-indirect
dispatch (spawn presets regs[1] == x20 == &fib_dispatch), dropping the
per-OS .global symbol entirely.
Fixes issue 0193 Bug A: the trampoline redesign bus-errored on the
go/wait/sleep capstone (1817) because fib_dispatch was not pinned to the
C ABI. Without an explicit ABI, fib_dispatch uses sx's internal calling
convention (x0 = implicit context, first arg self shifted to x1) while
the trampoline hands self over in x0 (C-ABI); on first entry the body
runs (x1 happens to alias self) but the closure then loads
regs[1] == &fib_dispatch as its first capture and re-invokes fib_dispatch
forever -> stack overflow -> bus error. Annotating fib_dispatch
`abi(.c)` pins it to the C-ABI (self in x0), matching the trampoline.
`abi(.c)` rather than `export` because the fn is reached only by address
through the trampoline, never by an external name -- so it needs the
convention, not a public symbol (it stays a local symbol). Root cause
found via lldb on an AOT build; confirmed against the compiler source.
Bug B (a top-level asm block wrapped in inline-if is dropped during the
comptime-conditional flatten) is carved out to issue 0194 (OPEN) -- no
live trigger remains, since the naked-fn trampoline sidesteps it.
1811/1814/1816/1817 run byte-identical on the aarch64-macOS host and in
an aarch64-linux container; full suite green (817/0). Documents the fiber
runtime in readme.md.
Port of std/sched.sx (the M:1 fiber runtime) to aarch64-linux. The epoll
bindings + std.event.Loop epoll backend are already committed and runtime-
validated (cc137002); this records the SCHEDULER port, which is WIP:
- WORKS, validated in an Apple `container` Linux VM: 1811 (round-robin) and 1816
(block_on_fd over the epoll fd path) run identically to macOS kqueue.
- Bug A: a register-indirect trampoline (naked fn + `br x20`, to avoid a per-OS
hand-written global-asm symbol) bus-errors on the 1817 go/wait/sleep capstone
on both platforms, though 1811/1816 work — unresolved.
- Bug B: wrapping the original global `asm` trampoline in an `inline if`/`case`
drops it (nm: fib_tramp U) in sched.sx's context, though every minimal repro
emits fine — a flatten/lowering interaction in src/imports.zig.
The WIP sched.sx port is preserved both in `git stash` and as
issues/0193-linux-fiber-port.patch. Two resolution paths (either suffices)
documented in the issue. sched.sx itself is left at HEAD (macOS green).
