diff --git a/Rsconscript b/Rsconscript
index 0dfea37..78b76b2 100644
--- a/Rsconscript
+++ b/Rsconscript
@@ -75,7 +75,7 @@ hel_env = env "hel", use: %w[ldc2 x86_64-w64-mingw32-gcc] do |env|
   env.add_builder(Image)
   env["sources"] = glob("src/hel/**/*.d")
   env["sources"] += glob("uefi-d/source/**/*.d")
-  env["DFLAGS"] += %w[-mtriple=x86_64-unknown-windows-coff --betterC -release -O3]
+  env["DFLAGS"] += %w[-mtriple=x86_64-unknown-windows-coff --betterC -release -O3 --wi]
   env["D_IMPORT_PATH"] += %w[src/hel uefi-d/source]
   env["LD"] = "x86_64-w64-mingw32-gcc"
   env["LDFLAGS"] += %w[-nostdlib -Wl,-dll -shared -Wl,--subsystem,10 -e efi_main -Wl,-Map,${_TARGET}.map]
diff --git a/src/hel/hel.d b/src/hel/hel.d
index 9a6b48d..4199ea3 100644
--- a/src/hel/hel.d
+++ b/src/hel/hel.d
@@ -10,6 +10,7 @@ extern (C) EFI_STATUS efi_main(EFI_HANDLE image_handle, EFI_SYSTEM_TABLE * st)
     st.ConOut.ClearScreen(st.ConOut);
 
     writeln("HOS EFI loader");
+    writeln("Firmware vendor: '%S', version: 0x%x", st.FirmwareVendor, st.FirmwareVendor);
     writeln("Press any key...");
 
     st.ConIn.Reset(st.ConIn, FALSE);
diff --git a/src/hel/output.d b/src/hel/output.d
index fa4e304..96506f4 100644
--- a/src/hel/output.d
+++ b/src/hel/output.d
@@ -1,21 +1,122 @@
 import uefi;
 import hel;
+import core.stdc.stdarg;
 
-void write(string s)
+private size_t format_hex(CHAR16 * s, ulong v, bool ptr)
+{
+    string hex_chars = "0123456789ABCDEF";
+    bool print = ptr;
+    size_t si = 0u;
+    for (size_t i = 0u; i < 16u; i++)
+    {
+        if (ptr && (i == 8u))
+        {
+            s[si++] = '_';
+        }
+        ulong n = (v >> (60u - 4u * i)) & 0xFu;
+        if (n != 0u)
+        {
+            print = true;
+        }
+        if (print || (i == 15u))
+        {
+            s[si++] = hex_chars[n];
+        }
+    }
+    return si;
+}
+
+private size_t format_dec(CHAR16 * s, ulong v)
+{
+    string dec_chars = "0123456789";
+    bool print;
+    char[20] buf;
+    size_t buf_i;
+    while ((buf_i == 0u) || (v != 0u))
+    {
+        ulong n = v % 10u;
+        buf[buf_i++] = dec_chars[n];
+        v /= 10u;
+    }
+    for (size_t si = 0u; si < buf_i; si++)
+    {
+        s[si] = buf[buf_i - si - 1u];
+    }
+    return buf_i;
+}
+
+void write(string s, va_list args)
 {
     __gshared static CHAR16[256] s16;
     size_t i = 0u;
-    while (i < s.length)
+    bool escape = false;
+    foreach (char c; s)
     {
-        s16[i] = s[i];
-        i++;
+        if (escape)
+        {
+            if (c == '%')
+            {
+                s16[i++] = '%';
+            }
+            else if (c == 'x')
+            {
+                ulong v;
+                va_arg(args, v);
+                i += format_hex(&s16[i], v, false);
+            }
+            else if (c == 'p')
+            {
+                ulong v;
+                va_arg(args, v);
+                i += format_hex(&s16[i], v, true);
+            }
+            else if (c == 'S')
+            {
+                const(CHAR16) * s2;
+                va_arg(args, s2);
+                for (size_t s2_i = 0u; s2[s2_i] != 0; s2_i++)
+                {
+                    s16[i++] = s2[s2_i];
+                }
+            }
+            else if (c == 'u')
+            {
+                ulong v;
+                va_arg(args, v);
+                i += format_dec(&s16[i], v);
+            }
+            else
+            {
+                s16[i++] = c;
+            }
+            escape = false;
+        }
+        else if (c == '%')
+        {
+            escape = true;
+        }
+        else
+        {
+            s16[i++] = c;
+        }
     }
     s16[i++] = 0u;
     g_st.ConOut.OutputString(g_st.ConOut, &s16[0]);
 }
 
-void writeln(string s)
+extern (C) void write(string s, ...)
 {
-    write(s);
-    write("\r\n");
+    va_list args;
+    va_start(args, s);
+    write(s, args);
+    va_end(args);
+}
+
+extern (C) void writeln(string s, ...)
+{
+    va_list args;
+    va_start(args, s);
+    write(s, args);
+    write("\r\n", args);
+    va_end(args);
 }