How to compile kernel?

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I have created a simple c kernel that prints Hello world and an another object file using nasm. my question is how to compile c kernel with gcc and after that create flat binary kernel by linking both object files and put on address 0x7e12. It should be 32bit kernel. I am on Lubuntu 14.04

What I have tried:

i have seen some samples and tired this but this does not give correct thing.

Compile.sh:

gcc -c kernel.c -o kernel.o
<br />nasm base.asm -f elf -o base.o
<br />ld -oformat=binary kernel.o base.o -Ttext=0x7e12

base.asm:

[bits 32]
[extern _start]

call _start

kernel.c:

C++

void start { char *v = (char*) 0xb8000; *v="M";}

Posted 6-Apr-17 21:01pm

Neonbird

Updated 6-Apr-17 21:44pm

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Jochen Arndt · Answer 1 · 2017-04-06T21:43:00

The first step is to fix the reported errors and warnings.

# gcc -c kernel.c
error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘{’ token

It must be

void start() { char *v = (char*) 0xb8000; *v="M";}

Next try:

# gcc -c kernel.c
warning: assignment makes integer from pointer without a cast

Understanding this error is a bit tricky. It complains about *v="M" because "M" is a pointer (to a constant string). Your code won't work as expected. You have to use a function that copies a string or assign each character:

void start() 
{ 
    char *v = (char*)0xb8000; 
    v[0] = 'M';
    v[1] = '\0';
}

I have nasm nowhere installed so I can't check it.

Regarding the linking read the documentation. The -T option requires to be followed by a script file.