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Hi there, if anybody still checks this forum? Anyway, I've been going back to my BOS source and started doing some work again. 
And I'm now sure that I'll base my drivers/programs on some relocatebale file format and not the segment approch, mainly becasue it's not supported on 64-bit systems, higher language compiler issues and so on.
While I research the executable format options I thought I might as well post my proof-of-concept segment based loading code here, in case anybody finds it useful!
It's not 100% completed, but you should be able to get a hang of how it works. It sets up new GDT selectors on the fly for each program/driver so that the ORG statement can be set to zero.
[b]drv_load.inc[/b]
;----------------------------------------------------------; ; BOS kernel Christoffer Bubach, 2005. ; ;----------------------------------------------------------; ; ; ; Handles all loading/unloading of drivers. ; ; ; ;----------------------------------------------------------; drv_selector dw 0 ; driver CS drv_offset dd 0 ; driver offset stack_pointer dd 0 ; temporary stack pointer driver_struct: ; space to save driver times 4096 dd 0 ; pointer. max 4096.. ;--------------------------------------------------------------------------; ; Load driver/program ; ; sets up mem and selectors for program.. ; ; ; ; in: ebx = address of app or 0 if it should be loaded ; ; ecx = size of app if already in mem ; ; dl = media # if it's to be loaded ; ; dh = 1 for driver/module, 0 for a program ; ; esi = ASCIIZ file name. eg. '/bubach/apps/test/test1.app', 0 ; ; '/bubach/drivers/mouse.drv', 0 ; ; ; ; ^----- Just forward to VFS that handles the rest ; ;--------------------------------------------------------------------------; load_module: cmp ebx, 0 jne .cont mov ax, 50-11 ; <- this is a fake-call.. ;) int 0x32 ; load via VFS .cont: cmp ecx, 0 je drv_error mov dl, 1 ; code sel. add ecx, 4096 ; add standard 4kb stack cmp dword [ebx+41], 'DRV_' ; sign. check jne drv_error ;-------------------------; ; add it to the list ; ;-------------------------; push ecx ; save size xor ecx, ecx .loop: cmp dword [driver_struct+ecx], 0 je .add_it inc ecx cmp ecx, 4096 jb .loop pop ecx jmp drv_error .add_it: mov dword [driver_struct+ecx], ebx pop ecx ; restore size push ebx ; save base and push ecx ; size mov dh, 1 ; 32bit thx call set_gdt mov word [drv_sel], cx ; store selector number pop ecx pop ebx mov dx, word [drv_sel] mov word [ebx+23], dx ; store CS selector # mov dl, 0 ; data sel. mov dh, 1 ; 32bit thx push ebx ; save base call set_gdt mov edx, ebx ; save allocate bytes pop ebx mov word [ebx+25], cx ; store DS selector # mov dword [ebx+27], edx ; store stack pointer mov dword [stack_pointer], esp ; store stackp. mov ax, word [ebx+25] mov ebx, dword [ebx] ; get init-pointer mov dword [drv_off], ebx ; save offset mov esp, edx ; set new stack, and push dword [stack_pointer] ; then mess with a local mov ds, ax ; variable for the last mov es, ax ; time before we set new mov fs, ax ; ds,es, fs mov ax, 0x10 ; and gs for mov gs, ax ; the driver. ;) db 0x9a ; far call drv_off dd 0 ; driver offset drv_sel dw 0 ; driver CS mov ax, 0x10 mov ds, ax mov es, ax mov fs, ax mov gs, ax pop esp ; our old stack pointer jmp quit_drv_load drv_error: xor eax, eax quit_drv_load: ret ;---------------------------------------------------------------; ; unload_driver - Unload driver/program ; ;---------------------------------------------------------------; ; in: ebx = driver address ; ; ecx = size ; ; ; ; out: eax = 1 if error, 0 if OK ; ;---------------------------------------------------------------; unload_module: ;--------------------------; ; remove driver from list ; ;--------------------------; push ecx ; save size xor ecx, ecx .loop: cmp dword [driver_struct+ecx], ebx je .remove_it inc ecx cmp ecx, 4096 jb .loop pop ecx jmp unload_error .remove_it: mov dword [driver_struct+ecx], 0 pop ecx ; restore size push ebx push ecx ; save info mov ecx, [ebx+4] mov dword [unl_off], ecx ; unload function offset mov cx, [ebx+23] mov word [unl_sel], cx ; unload func. code sel. mov ax, word [ebx+25] ; and data selector push ax ; save DS for later.. mov edx, dword [ebx+27] ; stack pointer mov dword [stack_pointer], esp ; store current stackp. mov esp, edx ; set new stack, and push dword [stack_pointer] ; then mess with a local mov ds, ax ; variable for the last mov es, ax ; time before we set new mov fs, ax ; ds,es, fs mov ax, 0x10 ; and gs for mov gs, ax ; the driver. ;) db 0x9a ; far call unl_off dd 0 ; driver offset unl_sel dw 0 ; driver CS ;cli ; BOCHS debug.. ;hlt mov ax, 0x10 mov ds, ax mov es, ax mov fs, ax mov gs, ax pop esp ;mov esp, dword [stack_pointer] pop bx ; saved DS from before call del_gdt ; data segment mov bx, [unl_sel] call del_gdt ; code segment pop ecx ; restore it pop ebx ;------------------; ; free memory ; ;------------------; ; cmp ebx, 0x100000 ; jb .low_mem ; call free_mem ; xor eax, eax ; jmp quit_drv_unl ; .low_mem: ; shr ebx, 10 ; / 1024 = 1 kb units ; call free_low_mem ; xor eax, eax ; jmp quit_drv_unl unload_error: mov eax, 1 ; error.. quit_drv_unl: ret
And my test driver, that sets up an interrupt service and then quits:
[b]test_drv.inc[/b]
use32 ;---------------------------------------------------; ; driver structure ; ; must be the first thing in all drivers ; ;---------------------------------------------------; driver_structure: dd init_driver ; sets up the syscalls etc dd deactivate ; unload, free mem and int db 'Test driver ' ; 15 bytes driver name dw 0 ; driver CS, to be filled dw 0 ; driver DS, to be filled dd 0 ; stack pointer.. dw 12345 ; Unique driver ID dd 0, 0 ; Reserved db 'DRV_V 0.01' ; 10 byte driver signature ;------------------------; ; other data ; ;------------------------; testing db ' Test driver: Init - Setting up int 0x33 for my test service..',0 testing2 db ' Test driver: INT 0x33 called!',0 testing3 db ' Test driver: Unloading myself..',0 ;---------------------------------------------------------------; ; init_driver - Start the driver, set up int(s) etc.. ; ;---------------------------------------------------------------; ; in: nothing ; ; ; ; out: nothing ; ;---------------------------------------------------------------; init_driver: pushad mov ax, 0x1e ; make new line int 0x32 mov ax, 0x1c ; print string mov esi, testing mov bl, 0x07 int 0x32 mov ax, 0x00 ; set up int mov cl, 0x33 ; # 0x33 mov dx, cs ; with current CS mov edi, interrupt_33 ; function pointer int 0x32 popad retf ;---------------------------------------------------------------; ; deactivate - Kill the driver, free mem and int(s). ; ;---------------------------------------------------------------; ; in: nothing ; ; ; ; out: nothing ; ;---------------------------------------------------------------; deactivate: push eax push ebx push esi mov ax, 0x1e ; make new line int 0x32 mov ax, 0x1c ; print string mov esi, testing3 mov bl, 0x07 int 0x32 pop esi pop ebx pop eax retf ;-------------------------------------; ; driver interrupt/service(s) ; ;-------------------------------------; interrupt_33: push gs push fs push ds push es push ax ; the code segment gets mov ax, [cs:0x19] ; adjusted by it's self mov ds, ax ; but I better fix ds, mov es, ax ; es.. mov fs, ax ; ..and fs. pop ax mov ax, 0x1e ; make new line int 0x32 mov ax, 0x1c ; print string mov esi, testing2 mov bl, 0x07 int 0x32 pop es pop ds pop fs pop gs iret
In my test case, i simply included the assembled binary for the "driver" at the end of my kernel, making it into one file, so code for loading via VFS and freeing memory at exit is stubs/dummy code.
As I said, not perfect or complete, but maybe it can give some ideas to those that think about using segmentation.
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Noticed now that I set the new app/driver stack, push my own stack pointer on there - to later pop after we get back control. No idea why I did that, since the stack pointer is saved to a local variable anyway... Seems like an uneccecary "risk" to let our own stack-pointer be exposed to the loaded program for no apparent reason.. Hmm, well it's not quality all the way, but might still give someone an idea of how it might be done.
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Hi,
Nice to see you back into it. I am slowly getting back into it too. I am trying to transition to 64-bit via CD/DVD/BD boot loading. I'm currently working that rather slowly. I will review what you go here, sounds kewl from the scanning I did.
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Hi, yeah it's great to have some motivation back. But unfortunatly I just got a rather bad case of the flu, so nothing done this weekend.. 
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Thanks, I'm actually already feeling better. Which is odd becasue I can usally be sick for a week or more 
Got my setup back where it should be, found me a floppy emulator for win7, did some batch file work to get the assemble->test time down and also started to get back into using boch debugger... I had forgotten most commands, which is scary, I hope my asm skills isn't in the same shape. But atleast I've fixed a natsy bug in my directory listing code, and I'll continue with full FAT12 support before looking more deeply into the exec format.
Sometimes I can have troubles focusing becasue I start drifting away from what I'm doing and looking ahead on stuff that I'd like to implement/support later on. Anyway, it's looking better each day, and I hope that I can find a balance in my life to give BOS a few hours every other day or so.
How far along are you with smiddyOS, have you done anything worth mentioning since last time I was active here? Haven't checked your webpage hosted here, but maybe you got a new one? Either way, it would be nice to get a chance to test your latest img-file 
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I have not done anything significant. I'm working on getting the CD/DVD/BD boot loading working. I'm nearly there. Then I will focus on moving to 64 bit. I haven't touched that site in ages. I know I've forgotten the password for sure. I think I tried a few weeks back to get on there, but failed. If you wish you can remove it. I appreciate you keeping it up BTW. If we ever meet in person I owe you a few beers (or your favorite beverage).
I need to find a balance too, which I'm working to simplify my life a bit more. I have been traveling nearly every week for the past two years and have essentially stopped that since I am transitioning jobs shortly.
How did school go? Did you finish? As I recall you were headed for college?
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Hehe, ok well as long as I keep this site there's no problem hosting it. But I could remove it if you want, doesn't matter to me either way.
Well I first went for a free-standing year called like "technical base-year" with basically all math, physics and chemistry... That was fun. Not. Think I managed to pass on like 50% of the courses, if that. But all I really needed was one of the earlier math courses so I could get in to the computer science program, which lasts for 3 years.
There I went for 2 years before dropping out, when my homepage wwwjoox.net took off. Too much money, too quickly kind of made me loose my footing. Eventually the site died, but pulled in a truckload of money while it was up.
I wish I had partied less, and planned ahead more, could have started a serious business, or invested in stock. All I did was waste every penny of it which left me with IRS-debt here.
Well, thats in the past now, and I'm slowly building up a more stable and serious web business while at the same time paying off my debts.
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@Bubach: I spent 7 years in college before getting my degree, there was some partying in there, and a transfer to another school. So now I do have my degree, but I have a home mortgage worth of student debt. It is going to take me some time to overcome that. A shame I can't transfer you some credits, I have enough for 2 degrees, one of which happens to be computer science with a focus in computer engineering/firmware.
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Wow, seven years? What I've heard about your college costs, it would seem that you are fortunate to have been able to pull it off at all. All education here is free, but you still have to support your own living with only around 400 dollars in government support each month, so rest is usually managed with student loans or extra work on the side.
Motivation was a big thing for me, what wasn't basic stuff that I knew since several years was so boring and unrelated that I lost all interest when the money started rolling in.
Anyway, won't need any degree since I'm still working on my own business - trying to get it back on track.
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$28,000 a year in school costs. That doesn't include living expenses. However, I had a scholarship that covered $10,000 a year for being brilliant;-). . I had a paid internship that covered most of my living expenses, then worked full time my last 2 years. The current president has made it possible to claim more of the loan interest on taxes for an extra couple years, however it would seem likely our gov't will change again this year, meaning I'll probably be picking up the debt of a rich man's son as well as my own.
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hehe, well yeah i guess
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