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Visual Basic 6 ​

Status: Planned — No implementation started.

Format ​

VB6 applications are compiled into Windows .exe or .dll files in one of two modes:

  • P-Code (pseudo-code) — compiled to VB6's proprietary bytecode VM; the default and most common
  • Native code — compiled to x86 machine code via MASM; much harder to decompile

The P-Code VM is well-documented through reverse engineering. The executable contains:

  • A PE header with the standard Windows executable structure
  • A VB6-specific header (VBHeader) with project name, threading model, and control references
  • P-Code bytecode in code segments, one per procedure
  • String and type information tables
  • COM object references (for controls: VBForm, TextBox, CommandButton, etc.)
  • Resource data (icons, bitmaps, dialogs)

Lifting Strategy ​

Full recompilation for P-Code (Tier 2). Native-code VB6 requires native decompilation (much harder, lower priority).

  1. Parse the PE file and locate the VB6-specific header
  2. Walk the project structure to find all forms, modules, and class modules
  3. Decode P-Code bytecode per procedure
  4. Identify VB6 runtime boundaries (MSVBVM60.DLL function imports)

VB6 is event-driven: forms have event handlers (Form_Load, Button1_Click, etc.) and properties. The object model maps cleanly to TypeScript classes.

What Needs Building ​

Format Parser (new crate: reincarnate-frontend-vb6) ​

  • [ ] PE header parser (or reuse an existing crate)
  • [ ] VB6 header (VBHeader, EXEPROJECTINFO) parser
  • [ ] Project structure walker: forms, standard modules, class modules
  • [ ] P-Code bytecode decoder — the P-Code instruction set is documented in community research (VB Decompiler, p-code research papers)
  • [ ] Form description extractor (control layout, property values, event bindings)
  • [ ] Type library references (for external COM control types)

P-Code Instruction Set ​

VB6 P-Code is a stack-based VM with ~200 opcodes. Key categories:

  • Load/store (local variables, module-level variables, properties)
  • Arithmetic (integer, single, double, currency, date)
  • String operations
  • Comparison and logical
  • Control flow (branch, call, return)
  • Object operations (COM dispatch: CreateObject, Set, Nothing, Is)
  • Collection operations (For Each, With)
  • Error handling (On Error GoTo, Resume)
  • Array operations (fixed-size and dynamic ReDim)
  • I/O operations (file-based: Open, Print #, Input #, Write #, etc.)
  • UI operations (form/control method calls via COM dispatch)

IR Mapping ​

  • VB6 procedure → IR function
  • Form_Load / Button1_Click → event handler functions
  • COM dispatch on controls → SystemCall("VB6.Control", methodName, args)
  • MsgBox → SystemCall("VB6.MsgBox", text, buttons, title)
  • InputBox → SystemCall("VB6.InputBox", prompt, title, default) + Yield
  • File I/O → SystemCall("VB6.File.Open", ...) etc.
  • DoEvents → Yield (yield to event loop)
  • Timer function → SystemCall("VB6.Timer")
  • Err object → error state in function context

Replacement Runtime (runtime/vb6/ts/) ​

VB6's object model is COM-based. The replacement runtime needs to model:

  • [ ] Form — window with title bar, resize, minimize, maximize, close
  • [ ] Label — text display
  • [ ] TextBox — single/multiline text input
  • [ ] CommandButton — button with click event
  • [ ] CheckBox / OptionButton — toggle/radio
  • [ ] ComboBox / ListBox — dropdown/list selection
  • [ ] Frame / PictureBox / Image — containers and image display
  • [ ] Timer control — recurring interval events
  • [ ] CommonDialog — file open/save dialog
  • [ ] MsgBox / InputBox — modal dialog functions
  • [ ] Printer object — print output (→ browser print API)
  • [ ] File I/O (Open, Close, Print #, Input #, Line Input #, Get, Put)
  • [ ] Registry access (GetSetting, SaveSetting) → localStorage
  • [ ] Clipboard (Clipboard.GetText, Clipboard.SetText) → navigator.clipboard
  • [ ] Date / Time / Now functions
  • [ ] Shell function — launch external program (→ web Worker or stub)

Known Challenges ​

  • Native code VB6 — If compiled with /native, the bytecode is x86. This is outside the Tier 2 scope; it would require a native decompiler (Ghidra, IDA). Much rarer in practice than P-Code.
  • COM controls — VB6 apps heavily use ActiveX controls (MSCOMCTL.OCX, Sheridan, Infragistics, etc.). The commonly used controls can be shimmed; obscure third-party ActiveX controls may be impossible to replicate.
  • Database access — Many VB6 apps use ADO/DAO for database access. These would map to IndexedDB or a backend API.
  • MDI forms — Multiple Document Interface forms (parent + child windows) have no direct web equivalent; need a window manager shim.
  • VB6 string type — VB6 String is a BSTR (COM string, length-prefixed, Unicode). Arithmetic on strings follows VB coercion rules, not JavaScript rules.

References ​