OSDev.org

Posted: **Mon Apr 10, 2017 3:52 pm**

Hello.

I try to make my bootloader, but have trouble with data address offset after linking.
Here my wlink config:

FILE MBR.asm.obj
FILE MBR.c.obj
NAME MBR.bin
OUTPUT raw
OPTION nodefaultlibs, quiet, start=_start
DISABLE 1014
ORDER
        clname CODE
        clname DATA
FORMAT dos

If use it, as a result all data addresses in program calculated as offsets from 0000.
If use next:

Code: Select all

FILE MBR.asm.obj
FILE MBR.c.obj
NAME MBR.bin
OUTPUT raw
        offset = 0x7c00
OPTION nodefaultlibs, quiet, start=_start
DISABLE 1014
ORDER
        clname CODE offset = 0x7c00
        clname DATA
FORMAT dos

It only use offset from 0x7c00 for code, but still use offset from 0000 for data.

If use next:

Code: Select all

FILE MBR.asm.obj
FILE MBR.c.obj
NAME MBR.bin
OUTPUT raw
        offset = 0x7c00
OPTION nodefaultlibs, quiet, start=_start
DISABLE 1014
ORDER
        clname CODE offset = 0x7c00
        clname DATA offset = 0x7d00
FORMAT dos

It generates valid program, puts data at offset 0x7d00 and use valid offset, but this version work only if my code < 0x100 byte and use hardcoded offset for data, so that is not good idea.

How I can set wlink to place DATA right after CODE and use global offset 0x7c00?

Posted: **Tue Apr 11, 2017 9:36 am**

Far be it from me to discourage you from using your favourite compiler, but Open Watcom is not widely used for OS development, which means that it can be a little difficult - compared to the more popular toolsets - to obtain the relevant information. A starting point is http://wiki.osdev.org/Watcom , but you may need to do further research.

Posted: **Tue Apr 11, 2017 11:19 am**

iansjack wrote:Far be it from me to discourage you from using your favourite compiler, but Open Watcom is not widely used for OS development, which means that it can be a little difficult - compared to the more popular toolsets - to obtain the relevant information. A starting point is http://wiki.osdev.org/Watcom , but you may need to do further research.

Can you help me find more suitable compiler and linker for this?
I use Watcom because it can without troubles link C with ASM, generate small code and support very old processors as 8086.

Posted: **Tue Apr 11, 2017 1:09 pm**

I'm afraid I can't make any suggestions as to a good toolkit for 8086 programming. I haven't written anything for it in decades.

Have you tried the Open Watcom forums? You are more likely to find someon who can help you there. (Although I believe that rdos - a user here - is a Watcom fan. Hopefully he will see your post and reply.)

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