Data transfers across segments

[jj1984]

Hi,

Assuming that privilege levels work out, is the following or any variation of the following allowed on Intel machines:

mov es:[ebx], fs:[eax]

That is, can you reach across data segments to move, add, etc. arguments?

 

[Cromewell]

In this case, I'd say write a small program and try it out, see what happens

 

[jj1984]

Haha... OK...

 

[jj1984]

Got an assembly error.

I forgot that direct memory to memory manipulations are forbidden; though, I don't see why a processor can't be constructed to allow such a thing.

 

[Cromewell]

I forgot that direct memory to memory manipulations are forbidden; though, I don't see why a processor can't be constructed to allow such a thing.

They can, just for the most part we didn't. The DEC VAX could, or more recently ARM11 based processors. There are others, but research in the 70s showed that it wasn't the most bit efficient.

 

[jj1984]

They can, just for the most part we didn't. The DEC VAX could, or more recently ARM11 based processors. There are others, but research in the 70s showed that it wasn't the most bit efficient.

What about other manipulations besides MOV?

For modern Intel systems, can we ADD two RAM locations directly or SUB, or compare, etc?

 

[Cromewell]

For modern Intel systems, can we ADD two RAM locations directly or SUB, or compare, etc?

Knowing what you found above what do you think?

 

[jj1984]

Knowing what you found above what do you think?

I would assume that we can't.

 

[Cromewell]

Good call