CODEWITHSUNDEEP
windowsx86loaderassemblyportable-executable
Nicolas Repiquet
Nicolas Repiquet

Reputation: 9265

Windows initial execution context

Once Windows has loaded an executable in memory and transfert execution to the entry point, do values in registers and stack are meaningful? If so, where can I find more informations about it?

Upvotes: 5

Views: 1837

Answers (2)

Pete
Pete

Reputation: 401

Chapter 5 of Windows Internals Fifth Edition covers the mechanism of Windows creating a process in detail. That would give you more information about Windows loading an executable in memory and transferring execution to the entry point.

I found this up-to-date reference that covers how registers are used in various calling conventions on various operating systems and by various compilers. It's quite detailed, and seems comprehensive: Agner Fog's Calling Conventions document

Upvotes: 1

Igor Skochinsky
Igor Skochinsky

Reputation: 25288

Officially, the registers at the entry point of PE file do not have defined values. You're supposed to use APIs, such as GetCommandLine to retrieve the information you need. However, since the kernel function that eventually transfers control to the entry point did not change much from the old days, some PE packers and malware started to rely on its peculiarities. The two more or less reliable registers are:

  • EAX points to the entry point of the application (because the kernel function uses call eax to jump to it)

  • EBX points to the Process Environment Block (PEB).

Upvotes: 8

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