Re: [Nasm-users] calling 'C' functions

[zak100 <zul...@ya...>]

Hi,
Thanks for your help. 
 

I have received your mz folder. It has two binaries: boot and image. 'boot'
is fine
but when i tried to load image to sector 2 it didnt work. Maybe I am doing
something 
wrong. However, I didnt find any 'C' files. Still waiting for your response
in this 
regard.

Zulfi.

Frank Kotler-3 wrote:
> 
> zak100 wrote:
>> Hi,
>> I am trying to call 'C" functions from my tiny kernel code. Can somebody
>> plz
>> help me with this?
>> ; call c function
>> extern [_K_main]
>> ;--- test kernel.bin---
>> 
>> ;    push cs
>> ;    push cs
>> ;    pop ds
>> ;    pop es
>>     mov ax, 7E0H
>>     mov ds,ax
>>     mov es,ax
>>     mov si, msg
>> 
>>     mov ah, 0Eh
>>     mov bx, 7
>> top:
>>     lodsb
>>     cmp al, 0
>>     jz blackhole
>>     int 10h
>>     jmp short top
>> 
>> blackhole:
>>     
>>     mov cx,1000
>>     Delay: Loop Delay
>>     call _K_main; this is in main.c
>>     hlt
>>     jmp blackhole
>> 
>> msg db 'Welcome to the Kernel!', 0
>> 
>> times 0x200-($-$$) db 0
>>         
>> 
>> I am getting following error mesg:
>> D:\nasm prog>nasm -f bin -o boot.bin test_kernel2.asm
>> test_kernel2.asm:5: error: label or instruction expected at start of line
> 
> Hi Zulfi,
> 
> Removing the brackets will at least give you correct syntax (extern 
> _K_main), but binary format still doesn't know about external 
> references. What format is your proposed _K_main in? OMF probably, for 
> 16-bit code(???).
> 
> Try assembling with "nasm -f obj test_kernel2.asm" this will produce 
> "test_kernel2.obj", by default. If your linker won't handle long file 
> names, you can shorten it with the "-o" switch, but your linker is 
> probably going to be happier with ".obj" than ".bin" (maybe not?).
> 
> Then... your linker is probably going to want to produce an MZ 
> executable by default. I don't think it's too hard to write a loader for 
> MZ, but it might be easier to persuade your linker to produce a .com 
> file. I believe ld (for 32-bit Linux - won't help you) can be coerced to 
> produce a flat binary, explicitly specifying origins for the various 
> sections (if you know how - I don't). If your linker will do that, 
> you're in luck. Failing that... I dunno.
> 
> Make sure your compiler isn't producing any "dosisms" in your C code, of 
> course.
> 
> The OS-development guys may have better advice on this.
> 
> Best,
> Frank
> 
> P.S. Thanks for asking here, rather than nasm-devel, Zulfi! :)
> 
> 
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