How to address above 4GB using assembly language ?

[prayag.ganoje]

Can any one tell me how to represent the physical address above 4GB using assembly language... viz

Code: Select all

DS:EDI

?

[JamesM]

Using PAE or long mode? In a x86_64 machine all registers are 64 bits long anyway...

[Brendan]

Hi,

Can any one tell me how to represent the physical address above 4GB using assembly language... viz

Code: Select all

DS:EDI

?

For 32-bit code you'd do it the exact same way you'd store any other 64-bit integer. For example, EDX might hold the highest 32-bits of the address and EAX might hold the lowest 32-bits.

If you're wondering how to access a 64-bit address in 32-bit assembly, the simple answer is you don't. Without paging you can't access anything above 4 GB, and with paging (PAE or PSE36) you're still using 32-bit linear addresses. To access a 64-bit physical address you need to map the page containing the address into the 32-bit linear address space, then use a 32-bit linear address to access it.


Cheers,

Brendan

[rv6502]

have a look at how EMS memory works, how a C128 can have more than 64KiB of ram, how a C64 can have 64KiB ram + 32Kib ROM, how a NES can access 1MiiB ROM cartridges, etc.

http://en.wikipedia.org/wiki/Bank_switching

you can implement something similar using paging

good luck