Pure Swift raw syscall to retrieve the name of a semaphore

psem.swift

import Foundation

struct psem_fdinfo {
    struct proc_fileinfo {
        var fi_openflags: UInt32
        var fi_status: UInt32
        var fi_offset: Int64
        var fi_type: Int32
        var fi_guardflags: UInt32
    }
    
    struct psem_info {
        struct vinfo_stat {
            var vst_dev: UInt32
            var vst_mode: UInt16
            var vst_nlink: UInt16
            var vst_ino: UInt64
            var vst_uid: UInt32
            var vst_gid: UInt32
            var vst_atime: Int64
            var vst_atimensec: Int64
            var vst_mtime: Int64
            var vst_mtimensec: Int64
            var vst_ctime: Int64
            var vst_ctimensec: Int64
            var vst_birthtime: Int64
            var vst_birthtimensec: Int64
            var vst_size: Int64
            var vst_blocks: Int64
            var vst_blksize: Int32
            var vst_flags: UInt32
            var vst_gen: UInt32
            var vst_rdev: UInt32
            var vst_qspare: (Int64, Int64)
        }
        
        var psem_stat: vinfo_stat
        // normally there would be a 1024 byte array here, but fixed sized arrays don't exist in Swift
    }
    var pfi: proc_fileinfo
    var psem: psem_info
}

let PROC_INFO_CALL_PIDFDINFO: UInt64 = 0x3
let PROC_PIDFDSEMINFO: UInt64 = 4

func sem_info(_ sem: Semaphore) -> (psem_fdinfo, String) {
    let syscall_ptr = dlsym(dlopen(nil, RTLD_NOW), "syscall")
    let syscall_sem_info = unsafeBitCast(syscall_ptr, to: (@convention(c)(
            Int32, // syscall #
            UInt64, UInt64, UInt64, UInt64, UInt64, UInt64, UInt64, // filler for x1-x7
            UInt64, // call #
            UInt64, // pid
            UInt64, // flavor
            UInt64, // arg (semaphore)
            UInt64, // buffer
            UInt64 // buffer_size
    ) -> Int32).self)
    
    let sem_info_size = 1184
    let sem_info_buf = UnsafeMutableRawPointer.allocate(byteCount: sem_info_size, alignment: 1)
        
    let s_ret = syscall_sem_info(
        SYS_proc_info,
        0, 0, 0, 0, 0, 0, 0, // filler for x1-x7
        PROC_INFO_CALL_PIDFDINFO,
        UInt64(getpid()),
        PROC_PIDFDSEMINFO,
        UInt64(UInt(bitPattern: sem)),
        UInt64(UInt(bitPattern: sem_info_buf)),
        UInt64(sem_info_size))
    
    assert (s_ret == Int32(sem_info_size))
    
    let sem_info = sem_info_buf.load(as: psem_fdinfo.self)
    let sem_name_raw = sem_info_buf.advanced(by: MemoryLayout<psem_fdinfo>.size).bindMemory(to: CChar.self, capacity: 1024)
    let sem_name = String(cString: sem_name_raw)
    
    return (sem_info, sem_name)
}