how would i get my (DOS) program to run all out of upper memory?

[miker00lz]

relatively new to C, but have used BASIC for many many years. i'm programming a program that takes over int 13h BIOS code and simulates a physical hard drive by accessing a raw image over TCP. what i'm not sure how to do is make my code run entirely out of the highest point in memory possible (highest under 640 KB that is) so that i can modify the BIOS data area to make the OS think the highest available block of memory is under my program's memory space. this way i can keep my routines in RAM while loading a boot sector over the network and jumping to it for a full boot over TCP.

otherwise, the newly booting instance of DOS/windows/linux would overwrite my code and that's certainly no good. any ideas?

[phantomotap]

Most (all?) modern operating systems will quickly load "protected mode" drivers to avoid the use of "int13"; therefore, such operating systems will avoid your code and its network images.

For example, you can do this with some older versions of Windows (Windows 98), but I don't think the Linux kernel has ever used "int13" (the loader may well read the kernel into memory using "int13").



However, you can use the technique to load an entire Linux kernel and customized initial image into memory (loaded entirely by the... loader); once your computer is "running under Linux" you can "chain" your way into virtually any operating system image stored on a network drive, floppy disc, or almost anything else. (Using some combination of "VirtualBox", "Grub", "SysLinux", and other such tools.)

Soma

[miker00lz]

Most (all?) modern operating systems will quickly load "protected mode" drivers to avoid the use of "int13"; therefore, such operating systems will avoid your code and its network images.

For example, you can do this with some older versions of Windows (Windows 98), but I don't think the Linux kernel has ever used "int13" (the loader may well read the kernel into memory using "int13").



However, you can use the technique to load an entire Linux kernel and customized initial image into memory (loaded entirely by the... loader); once your computer is "running under Linux" you can "chain" your way into virtually any operating system image stored on a network drive, floppy disc, or almost anything else. (Using some combination of "VirtualBox", "Grub", "SysLinux", and other such tools.)

Soma

you can actually make linux use the bios routines if the option is enabled in the kernel. it's in there as a fallback. i'm mostly just writing to this get some more practice at C.

[Salem]

There are plenty of things to practice on which are a hell of a lot easier to debug than boot loaders "Hey, where did I put my OS install disks?"

[rags_to_riches]

Cross-posted

[miker00lz]

There are plenty of things to practice on which are a hell of a lot easier to debug than boot loaders "Hey, where did I put my OS install disks?"

i've mostly got all the code written already, just needed some info on this. this isn't technically a boot loader, either. it's more of a.... boot loader loader. õ_ô

[User Name:]

you can actually make linux use the bios routines if the option is enabled in the kernel. it's in there as a fallback. i'm mostly just writing to this get some more practice at C.

Yeah, that's kind of impossible... Once in protected mode, int 13, along with all ints from 0 to 31h, are reserved for cpu exceptions.