Low-level syscall primitives for Go on Linux, Darwin, and experimental FreeBSD.

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zcall provides low-level syscall entry points that bypass Go's runtime syscall machinery (entersyscall/exitsyscall). It targets code paths that need direct control over syscall boundaries, such as io_uring submission.

• Direct syscall entry points, provided through assembly stubs for each platform.
• Kernel-style return values, with wrappers returning the raw result alongside errno.
• Syscall numbers and related constants defined internally, without depending on syscall or x/sys/unix.
• Platform-specific implementations selected through build tags.

• Primitive entry points for 4-argument and 6-argument syscalls.
• Wrappers for common I/O, socket, memory, and socket-option operations.
• Linux-specific helpers for network link queries, special file descriptors, zero-copy operations, and io_uring.

go get code.hybscloud.com/zcall

msg := []byte("Hello from zcall!\n")
// Direct kernel write to stdout
_, _ = zcall.Write(1, msg)

msg := []byte("hello\n")
n, errno := zcall.Write(1, msg)
if errno != 0 {
	return zcall.Errno(errno)
}

fd, errno := zcall.Socket(zcall.AF_INET, zcall.SOCK_STREAM|zcall.SOCK_NONBLOCK|zcall.SOCK_CLOEXEC, 0)
if errno != 0 {
	return zcall.Errno(errno)
}
defer zcall.Close(fd)

links, err := zcall.Links()
if err != nil {
	return err
}

// 4-argument syscall
Syscall4(num, a1, a2, a3, a4 uintptr) (r1, errno uintptr)

// 6-argument syscall
Syscall6(num, a1, a2, a3, a4, a5, a6 uintptr) (r1, errno uintptr)

┌─────────────────────────────────────────────────────────┐
│                    User Application                     │
├─────────────────────────────────────────────────────────┤
│                      zcall API                          │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────────┐  │
│  │  Syscall4   │  │  Syscall6   │  │ Convenience API │  │
│  └──────┬──────┘  └──────┬──────┘  └────────┬────────┘  │
├─────────┴────────────────┴─────────────────┴────────────┤
│                  internal/asm_*.s                       │
│         Raw Assembly (SYSCALL / SVC / ECALL)            │
├─────────────────────────────────────────────────────────┤
│                     Operating System                    │
└─────────────────────────────────────────────────────────┘

MIT — see LICENSE.

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