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ABI_SYSCALL.md

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Compat Syscall ABI (clan-abi-v1)

Frozen snapshot of scopes 1–100 compat syscall surface. Native syscall IDs are reserved separately (scope 107+); they must not redefine compat numbers.

See: AXIOMS.md, USER_SYSCALLS.md, ABI_STABILITY.md, ABI_SECURITY.md.

Register ABI (x86_64 hardware path)

Register Role
rax Syscall ID
rdi arg0
rsi arg1
rdx arg2

Entry: syscall instruction → kernel trampoline → sysret return.

Scope 81 validates real sysret path (HW_SYSRET_REAL counter).

Allowlisted hardware syscalls (scope 100)

From kernel/src/user_syscall_hw.rs ALLOWED_HW_SYSCALLS:

ID Name Notes
1 GetTickCount
60 UserCopyProbe copyin validation
61 ExitProcess
62 WaitProcess
63 ReadFileProbe
64 WriteFileProbe
65 ReadPathProbe path string — compat
66 OpenFile path — compat
67 CloseFile
68 ReadFd
69 WriteFd
70 DupFd
71 Mprotect
72 Mmap
73 WritePathProbe
74 Chdir
75 Munmap
76 ForkLite
77 Fcntl
78 WaitLite
79 GetCwd
80 Pipe PipeLite — compat IPC
81 ExecLite
82 Poll PollLite — compat

Signal delivery syscalls (83–86) are documented in docs/architecture/ when the signal subsystem is linked; they are not yet in the HW dispatch table.

Kernel-internal IDs 2–59 (counters, telemetry) exist in SyscallId but are not in the Ring 3 hardware allowlist unless invoked from kernel/shell paths.

Error encoding (compat)

SyscallError: InvalidSyscall, InvalidArgument, Storage — returned via dispatcher; user copy paths use probe counters.

Native errors (future) will use a separate enum bound to clan-semantics-v*.

Native ID space (kernel smokes; ring-3 allowlist deferred to scope 128 G4)

Range Owner
1–82 Compat (frozen clan-abi-v1)
256+ Native caps, endpoints, async wait

Native syscalls must not expose path-string open for native processes (ABI_SECURITY.md).

Native syscall IDs (scope 112)

Kernel-only dispatch via kernel/src/native_syscall.rs — not in ALLOWED_HW_SYSCALLS until scope 128.

ID Name Notes
256 CapCreate Mint cap (arg0=ObjectId, arg1=rights mask)
257 CapClose Close cap slot arg0
258 CapTransfer Move cap arg0 to process arg1

PipeLite compat bridge

Pipe = 80 creates /@pipe/{id}/r and /@pipe/{id}/w FD paths (kernel/src/pipe.rs). Native Endpoint objects supersede this for native apps (scope 134+); compat unchanged (spec E-* compat preservation).