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points by ihavesomeexampl 3 days ago | 0 comments

But.. alter data that gets executed (interpeter?), I mean, how does this work even in theory? All data is potentially code?

[–] AdamH12113 3 days ago

To clarify what intrasight is talking about: A Harvard architecture CPU has two physically separate memory busses for code and data. This makes it possible to build a computer with a program memory that cannot be altered through the data bus. In practice, this isn't normally done -- even on Harvard architecture microcontrollers, the flash and RAM are connected to both busses because memory is expensive. And having inalterable program memory doesn't save you from stack-smashing attacks that alter a return address.

[–] intrasight 3 days ago

All data is potentially code only in a Von Neumann architecture, but not in a Harvard architecture, where there's a separation of data and code with different memory access to each.

[–] esterna 3 days ago

Code and data being equivalent is a consequence of Turing completeness; you can always write a Python interpreter, point it at "data" and have it execute that via interpretation.

[–] lelanthran 3 days ago

> All data is potentially code only in a Von Neumann architecture, but not in a Harvard architecture, where there's a separation of data and code with different memory access to each.

Says you. I wrote a program for a Hardvard architecture chip (PIC) that read bytecode from the data memory and executed it. Updates were made by replacing the data block with a new data block.

In practice, there is no way to separate data and instructions. After all, JS downloaded inside a webpage is literally data, and it gets executed.