Personalities

A personality is the OS ABI a process expects. Every context carries one, and it drives syscall dispatch, argument translation, error encoding, signals, and process startup.

Supported personalities

Personality	Value	Binary format	Status
Kernel (native)	0	ELF (native)	Native ABI, default
Linux	1	ELF (OS/ABI 0 or 3)	~80/450 syscalls mapped
Windows (NT)	2	PE (machine 0x8664 / 0xAA64)	Not started
Darwin (macOS)	3	Mach-O (x86_64 / arm64)	Not started
FreeBSD	4	ELF (OS/ABI 9)	Not started
NetBSD	5	ELF (OS/ABI 2)	Not started
OpenBSD	6	ELF (OS/ABI 12)	Not started

The numeric values are the on-wire representation stored in each Context and shared with the Zig layer; they match the C enum in include/personality.h.

Detection

Personality is detected from the binary during exec(), before the first return to userspace. The Zig layer provides the detection helpers:

ELF — fromElfOsAbi(osabi, machine)

Reads e_ident[EI_OSABI]:

OS/ABI byte	Meaning	Personality
0	ELFOSABI_NONE (System V)	Linux (most common default)
3	ELFOSABI_LINUX / GNU	Linux
9	ELFOSABI_FREEBSD	FreeBSD
2	ELFOSABI_NETBSD	NetBSD
12	ELFOSABI_OPENBSD	OpenBSD
other	—	native kernel

Modern Linux toolchains emit ELFOSABI_NONE, so 0 is treated as Linux by default; the loader may override based on other signals.

PE — fromPe(machine, subsystem)

Maps the PE machine type (0x8664 AMD64, 0xAA64 ARM64, 0x14C i386, …) to the Windows personality.

Mach-O — fromMachO(cputype, filetype)

Maps the Mach-O cputype (0x01000000 arm64, 0x00000007 x86_64, …) to the Darwin personality.

Wiring status

These helpers are implemented and unit-tested in Zig, but the Rust exec() path does not yet call them — contexts currently default to the native personality. Wiring this is part of the M1 milestone. See ELF & ABI spec.

Per-OS conventions

Different personalities encode results differently. The Zig dispatcher re-encodes the kernel's -errno/value convention into:

• Linux — negative errno in the return register (no carry flag on x86_64).
• Windows — NTSTATUS return convention.
• *Darwin / BSD — error signalled via the carry flag on x86_64 (value in the return register otherwise).

Adding a new personality

1. Add a variant to the Personality enum (personality/src/personality.zig).
2. Add a detection clause in fromElfOsAbi() / fromPe() / fromMachO().
3. Create personality/src/<name>/tables.zig with the syscall-number table.
4. Create personality/src/<name>/shim.zig with argument/structure translators.
5. Wire dispatch in personality/src/main.zig.
6. Add binary-format loading on the Rust side (src/elf.rs, future src/pe.rs / src/macho.rs).

See the generated Personality Components for the current Zig surface.