LinuxInterop.cs

namespace VaListInterop
{
    using System;
    using System.Runtime.InteropServices;

    public static class LinuxInterop
    {
        [DllImport("libdl", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        public static extern IntPtr dlsym(IntPtr handle, string symbol);

        [DllImport("libdl", CallingConvention = CallingConvention.Cdecl)]
        public static extern bool dlclose(IntPtr handle);

        public const int RTLD_LAZY = 1;
        [DllImport("libdl", CallingConvention = CallingConvention.Cdecl)]
        public static extern IntPtr dlopen(string lpFileName, int flags);

        [DllImport("libdl", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        public static extern string dlerror();


        /// <summary>
        /// Format a string using printf style markers
        /// </summary>
        /// <remarks>
        /// See https://stackoverflow.com/a/37629480/2663813
        /// </remarks>
        /// <param name="buffer">The output buffer (should be large enough, use _vscprintf)</param>
        /// <param name="format">The message format</param>
        /// <param name="args">The variable arguments list pointer. We do not know what it is, but the pointer must be given as-is from C back to sprintf.</param>
        /// <returns>A negative value on failure, the number of characters written otherwise.</returns>
        [DllImport("libc", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        public static extern int vsprintf(
            IntPtr buffer,
            [In][MarshalAs(UnmanagedType.LPStr)] string format,
            IntPtr args);

        /// <summary>
        /// Compute the size required by vsprintf to print the parameters.
        /// </summary>
        /// <param name="format"></param>
        /// <param name="ptr"></param>
        /// <returns></returns>
        [DllImport("libc", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
        public static extern int vsnprintf(
            IntPtr buffer,
            UIntPtr size,
            [In][MarshalAs(UnmanagedType.LPStr)] string format,
            IntPtr args);
    }
    
    /// <summary>
    /// The va_list structure of linux x64
    /// https://www.uclibc.org/docs/psABI-x86_64.pdf page 52
    /// </summary>
    [StructLayout(LayoutKind.Sequential, Pack = 4)]
    public struct VaListLinuxX64
    {
        private UInt32 gp_offset;
        private UInt32 fp_offset;
        private IntPtr overflow_arg_area;
        private IntPtr reg_save_area;
    }
}