[SOLVED] a kernel i wrote myself cannot find data

smeezekitty · 09-30-2009, 08:40 PM

for example if i put

Code:

kernel_print("Hey!");

the cursor moves 4 spaces but i see nothing on screen

manu-tm · 09-30-2009, 09:15 PM

What do you mean exactly? Did you compile the kernel or develop one on your own? And you must give much more info because I have no idea about what you want to know...

smeezekitty · 09-30-2009, 10:13 PM

i developed it from scratch and got the bootloader from theNbomr
it bootloads and runs but string litterals cannot be read

smeezekitty · 09-30-2009, 11:50 PM

ok let me MAKE MY SELF CLEAR
i wrote a kernel from scratch and had a F### of a time getting it to work
i finnaly got it to work but i cannot read anything in the data segment
i think that DS is set wrong but i really ddo not know how to fix it
so could someone with experence please help me?

manu-tm · 10-01-2009, 07:42 AM

I understand now but I have no experience in this, sorry. You use assembly?

ntubski · 10-01-2009, 10:33 AM

Unless you are doing something fancy, you should use the flat memory model, so DS should be same as the other segments. EDIT: didn't realize this is a 16-bit kernel.

Does it work if you print data from the stack?

Code:

char str[] = "Hey!";
kernel_print(str);

smeezekitty · 10-01-2009, 01:29 PM

Quote:

Originally Posted by ntubski

Unless you are doing something fancy, you should use the flat memory model, so DS should be same as the other segments. Does it work if you print data from the stack?

Code:

char str[] = "Hey!";
kernel_print(str);

no but this does:

Code:

char str[5];
str[0] = 'H';
str[1] = 'e';
str[2] = 'y';
str[3] = '!';
str[4] = 0;
kernel_print(string);

yours did not work because it still had a constant

johnsfine · 10-01-2009, 02:48 PM

If your goal is the "tiny" memory model (CS == DS == SS) then you should make sure your tool chain is linking that way and you should have your startup code copy CS to both DS and SS.

Your failure to get DS right, could represent either or both of the above are wrong.

If your goal is some other memory model, make sure you understand what memory model you want and how to get the tool chain to compile/link for that memory model and how to make your startup code initialize for that memory model.

Quote:

Originally Posted by smeezekitty

no but this does:

Code:

char str[5];
str[0] = 'H';
str[1] = 'e';
str[2] = 'y';
str[3] = '!';
str[4] = 0;
kernel_print(string);

That working indicates that DS == SS. It does not indicate that either DS or SS is correct and it doesn't indicate that you are linking correctly for the desired memory model.

Quote:

Originally Posted by ntubski

you should use the flat memory model

There is not complete agreement on the terminology, but usually "flat" memory model implies the offset size is at least 32 bits. In 16 bit programming, the "flat" memory model is usually called the "tiny" memory model.

So if you want to look up in your tool chain documentation how to get that memory model, you'll have an easier time using the common terminology.

You can find that terminology documented at:

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

The default memory model in 16 bit tool chains is "small". CS < DS == SS. If you want "small" memory model, you need to figure out how to make your startup code initialize DS and SS with the correct value.

smeezekitty · 10-01-2009, 02:57 PM

let me post the batch file i used to compile it
just a second

smeezekitty · 10-01-2009, 03:02 PM

Code:

tasm call.asm
nasm16 -f bin -o bnl.bin boot.asm
tcc -c nodos.c
tlink /n call+nodos, _k.exe
exetobin _k.exe kernel.ker
copy /b bnl.bin+kernel.ker kernel.out
copy kernel.ker dbg.com

dbg.com is to be debugged with a debugger
kernel.out is the bootable image

johnsfine · 10-01-2009, 03:09 PM

Quote:

Originally Posted by smeezekitty

let me post the batch file i used to compile it

It has been many years since I used tlink. I expect the same is true for almost anyone else here who ever used it.

I certainly don't remember tlink command line switches for tiny memory model, nor do I remember where my copy of tlink documentation is.

If you have an easy URL for tlink documentation, I might take a look and then explain the relevant switches.

smeezekitty · 10-01-2009, 03:24 PM

i copy and pasted this from the output of tlink

Code:

  /3      │ Enables processing of 32-bit modules
  /A      │ Specifies segment alignment
  /c      │ Treats case as significant in symbols
  /d      │ Warns of duplicate symbols in libraries
  /e      │ Ignores Extended Dictionary
  /i      │ Initializes all segments
  /l      │ Includes source line numbers
  /L      │ Specifies library search paths
  /m      │ Creates map file with publics
  /n      │ Doesn't use default libraries
  /o      │ Overlays following modules or libraries
  /s      │ Creates detailed map of segments
  /t      │ Generates .COM file. (Also /Tdc.)
  /Td     │ Creates target DOS executable
  /Tdc    │ Creates target DOS .COM file
  /Tde    │ Creates target DOS .EXE file
  /v      │ Includes full symbolic debug information
  /x      │ Does not create map file
  /ye     │ Uses expanded memory for swapping
  /yx     │ Configures TLINK's use of extended memory
  /r      │ Restores the AX register on return

johnsfine · 10-01-2009, 03:44 PM

I thought you could get tlink to generate tiny memory model after tcc compiles object files for small memory model. Maybe you can by specifying /t which also makes the output a .com instead of a .exe. Or maybe I'm misremembering and you need a switch to tcc to get tiny memory model instead of small.

Do you understand which you want "tiny" or "small"?

I don't recall the exetobin program. A .com is a flat binary format normally used with tiny memory model, but there is an implied extra 0x100 bytes at the beginning. Does exetobin also have an implied extra 0x100 bytes?

All those details must be coordinated between your loader and startup code and the way you use the tool chain.

smeezekitty · 10-01-2009, 03:48 PM

yes it converts .exe to .com files
because if i tell the linker to do it i get an error (Error: Cannot generate COM file : invalid initial entry point address)

smeezekitty · 10-01-2009, 04:35 PM

I attach the a dissasmebley of most of the kernel below
i will release the full C source when i am done with it