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Version analysis of David23

This code appears in the following versions (click to see it in the source code):

Code variations between these versions are shown below.

Name: David23 Type: Variable Category: Copy protection Summary: Address pointer to the start of the 6502 stack
This two-byte address points to the start of the 6502 stack, which descends from the end of page 2, less LEN bytes, which comes out as &01DF. So when we push 33 bytes onto the stack (LEN being 33), this address will point to the start of those bytes, which means we can push executable code onto the stack and run it by calling this address with a JMP (David23) instruction. Sneaky stuff!

Code variation 1 of 1Specific to an individual platform

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EQUW (512-LEN) \ The address of LEN bytes before the start of the stack
EQUW 6 \ This value is not used in this unprotected version of \ the loader, though why the crackers set it to 6 is a \ mystery