danos/system/abi.zig

//! The **private kernel ↔ runtime** ABI: the raw system_call contract — the call
//! numbers, `mmap` protection flags, the page size those calls work in, and the IPC
//! name-registry ids and notification bit. Shared by the kernel dispatcher
//! (system/kernel/process.zig) and the user-space runtime library (library/runtime/),
//! so the two can never drift.
//!
//! **Application code does not speak this.** danos programs call the `runtime` library —
//! the stable, danos-native ABI — and the runtime is the one thing that issues the
//! actual system calls (POSIX code layers over the runtime, never on this directly). It
//! is the same split as libSystem on macOS or win32 over the NT syscalls: the numbers
//! here are an implementation detail the runtime hides and may renumber, not a public
//! interface. See docs/coding-standards.md and library/runtime/.
//!
//! This is the *core* contract; the device half — `DeviceDescriptor` and friends, which
//! also cross this boundary — lives with the device sub-project as [[device-abi]]
//! (system/devices/device-abi.zig). The loader↔kernel handoff is [[boot-handoff]].

/// Page size every `mmap`/`munmap` grant and the boot memory map are measured in.
/// 4 KiB on every architecture danos targets so far. Part of the ABI because the
/// runtime aligns to it (grants are page-granular) and the kernel guarantees it.
pub const page_size = 4096;

/// The kernel system_call numbers — the single source of truth shared by the kernel
/// dispatcher (system/kernel/process.zig) and the user runtime library, so the two
/// can never drift. The set is deliberately microkernel-minimal: file/device I/O
/// is not here — it lives in user-space servers reached through the IPC calls.
/// The table grows one milestone at a time; see docs/syscall.md.
pub const SystemCall = enum(u64) {
    exit = 0, // exit(code): end the calling process
    yield = 1, // yield(): give up the rest of this quantum
    debug_write = 2, // debug_write(ptr, len): raw bytes to the kernel log (bring-up only)
    sleep = 3, // sleep(ms): block the caller for ms milliseconds
    mmap = 4, // mmap(len, prot) -> base: grant zeroed, page-aligned user pages
    munmap = 5, // munmap(base, len): release pages from a prior mmap
    create_ipc_endpoint = 6, // create_ipc_endpoint() -> handle: a new IPC endpoint
    ipc_register = 7, // ipc_register(service_id, handle): publish an endpoint by well-known id
    ipc_lookup = 8, // ipc_lookup(service_id) -> handle: find a published endpoint
    ipc_call = 9, // ipc_call(h, message, len, reply, cap) -> reply_len: send + block for reply
    ipc_reply_wait = 10, // ipc_reply_wait(h, reply, len, receive, cap) -> receive_len (+badge in rdx)
    device_enumerate = 11, // device_enumerate(buffer, maximum) -> count: snapshot the device table
    device_claim = 12, // device_claim(id) -> ok: take exclusive ownership of a device
    mmio_map = 13, // mmio_map(id, resource_index) -> vaddr: map a claimed device's MMIO into this AS
    irq_bind = 14, // irq_bind(id, resource_index, endpoint): deliver a device IRQ as an IPC notification
    irq_ack = 15, // irq_ack(id, resource_index): re-arm a bound IRQ after servicing it
    device_register = 16, // device_register(parent_id, descriptor) -> id: publish a child of a device you claimed
    system_spawn = 17, // system_spawn(name_ptr, name_len) -> 0: start a named initial-ramdisk binary as a new ring-3 process
    dma_alloc = 18, // dma_alloc(len, flags) -> vaddr (rax), paddr (rdx): contiguous, pinned, uncacheable DMA memory
    dma_free = 19, // dma_free(vaddr, len) -> 0: release a prior dma_alloc
    msi_bind = 20, // msi_bind(device_id, endpoint) -> address (rax), data (rdx): a per-device MSI vector for a claimed device
    io_read = 21, // io_read(device_id, resource_index, offset, width) -> value: read a port in a claimed device's io_port resource
    io_write = 22, // io_write(device_id, resource_index, offset, width, value) -> 0: write a port in a claimed device's io_port resource
    clock = 23, // clock() -> nanoseconds since boot: a monotonic time source (for timeouts/delays)
    _,
};

/// The x86 MSI message address base (`0xFEE0_0000`): a device raises an MSI by writing
/// `data` to this address, which the Local APIC turns into an interrupt at the vector
/// in `data`. The kernel returns the concrete (address, data) from `msi_bind`; this is
/// the fixed prefix, exposed so a driver's config-space programming reads clearly.
pub const msi_address_base: u64 = 0xFEE0_0000;

/// `dma_alloc` flags. `coherent` (uncacheable) is the portable default; the others are
/// opt-in for specific hardware. `write_combining` needs PAT programming (not yet — it
/// currently falls back to coherent); see docs/driver-model.md (M14).
pub const dma_coherent: u64 = 1; // strong-uncacheable — the default, the only portable one
pub const dma_write_combining: u64 = 2; // write-combining (framebuffers); needs PAT
pub const dma_below_4g: u64 = 4; // physical address must fit 32 bits (legacy DMA engines)

/// Set in the badge returned by `ipc_reply_wait` when what arrived is an
/// **asynchronous notification** (today: a device interrupt bound with `irq_bind`)
/// rather than a message from a client. There is no payload and no reply owed; the
/// low bits carry the source, a GSI. Shared so the kernel's ISR and the driver's
/// event loop can't disagree about which bit means "the hardware spoke".
pub const notify_badge_bit: u64 = 1 << 63;

/// Well-known IPC service ids for the bootstrap name registry (create_ipc_endpoint +
/// ipc_register/ipc_lookup). Small integers, so no string interning is needed
/// during bring-up. The VFS server registers under `vfs`; clients look it up.
pub const ServiceId = enum(u32) {
    vfs = 1,
    _,
};

/// Protection flags for `mmap` (matching the usual C bit values).
pub const prot_read: u64 = 1;
pub const prot_write: u64 = 2;
pub const prot_exec: u64 = 4;

/// `send_cap` / `received_cap` sentinel meaning "no capability" on the `ipc_call` /
/// `ipc_reply_wait` cap-passing path (M13). `~0`, like `no_parent` — a real handle is
/// a small index, so it can never collide.
pub const no_cap: u64 = ~@as(u64, 0);