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A Deep Dive into the Turbo Pascal Compiled Code

Overview

This is a walkthrough through the compiled code of an basic Pascal program that does nothing. The source was compiled under Turbo Pascal 7.0 (TP7). Because TP7 uses Smart Linking, the final .EXE file will not contain any code or variable that is not called, used, or referenced. The main content within these pages refer to this basic Pascal program. On the final section (Functions/Procedures), we attempt to disassemble and analyze System Library functions and procedures that are normally not included in final .EXE generated for the basic Pascal program. That section will be updated and expanded as we are able to analyze more code.

Table of Contents

• Files in this repository
• System Data
• Text File Type
• File Modes
• DOS Standard Handles
• Main Program
• System Library (Minimal)
  • 0000 Initialize System Library
  • 0088 Initialize Input File Record
  • 009C Initialize Output File Record
  • 00B1 Test for 8086/80186/80286
  • 00D6 Heap error exit routine
  • 00DB Critical Error Handler
  • 0104 Overlay manager not installed error
  • 010C INT 00h Handler
  • 0113 Ctrl-C / INT 23h Handler
  • 018B Flush and Close Input and Output Files
  • 019D Restore interrupt vectors
  • 01B7 Print Runtime error
  • 01E9 DOS Exit
  • 01F0 Print string
  • 01FE Convert number to ASCII
  • 0218 Print digits
  • 0232 Print character
  • 0239 Interrupt List
  • 024C Runtime error strings
  • 0263 Empty string and Hidden Copyright string
  • 02C1 Range check error
  • 02C7 Arithmetic overflow error
  • 02CD Check stack
  • 02E6 Assign Function
  • 0364 Reset/Rewrite Function
  • 03BA Reset/Rewrite Function (II)
  • 03FA I/O Function Dispatcher
  • 040B Read Function
  • 043B Write to File Function
  • 0460 Write Function
  • 0480 Close Function
  • 0499 Open Function
  • 0526 Open Function (II)
  • 0580 Clear input/output file records and interrupt vector array
• Runtime Error Codes
• Functions and Procedures
  • 8087/80287/80387 x87 Control Word
  • 8087/80287/80387 x87 Status Word
  • 8087/80287/80387 x87 FPU Evironment
  • 8087/80287/80387 Temporary data
  • Identify 8087/80287/80387 FPU
  • Initialize 8087/80287/80387
  • Ports used by 8087/80287/80387
  • Randomize
  • Random Number Generator Engine
  • Random: Real
  • Random: Real, FPU: 87/287/387
  • Random(Int): Int
  • Real Type
  • Convert Real Number to String
  • Print Real Number