I made a simple hello world ,, kernel ''. It doesn't print anything. What did I do wrong?

Question

I have followed this tutorial: https://www.youtube.com/watch?v=1rnA6wpF0o4 in order to write a very very basic hello world after boot, as it seems very complete on the next episodes. My problem is that I cannot see what I've done wrong as I verified twice if my code is exactly the same as in the video. It passes grub and then it is just black screen instead of printing the message. I have tried connecting to the forum in the description to ask questions but it is in German and forum page does not load.

So here are the sources: kernel.cpp

void printf(char *str)
{
    unsigned short* VideoMemory = (unsigned short*)0xb8000;
    for(int i=0; str[i]!= '\0'; ++i)
        VideoMemory[i]=(VideoMemory[i] & 0xFF00) | str[i];
}

extern "C" void kernelMain(void* multiboot_structure, unsigned int magicnumber)
{
    printf("Hello World!");
    while(1);
}

linker.ld

ENTRY(loader)
OUTPUT_FORMAT(elf32-i386)
OUTPUT_ARCH(i386:i386)

SECTIONS 
{
    . = 0x0100000;
    
    .text :
    {
     *(.multiboot)
     *(.text*)
     *(.rodata)
    }
    
    .data :
    {
        start_ctors = .;
        KEEP(*( .init_array ));
        KEEP(*(SORT_BY_INIT_PRIORITY( .init_array.* )));
        end_ctors = .;
        
        *(.data)
    }
    
    .bss :
    {
        *(.bss)
    }
    
    /DISCARD/ : 
    {
        *(.fini_array*)
        *(.comment)
    }
}

loader.s

.set MAGIC, 0x1badb002
.set FLAGS, (1<<0 | 1<<1)
.set CHECKSUM, -(MAGIC + FLAGS)

.section .multiboot
    .long MAGIC
    .long FLAGS
    .long CHECKSUM


.section .text
.extern kernelMain
.global loader

loader:
    mov $kernel_stack, %esp
    push %eax
    push %ebx
    call kernelMain
    
_stop:
    cli
    hlt
    jmp _stop
    
.section .bss
.space 2*1024*1024 # 2 MiB
kernel_stack:

and Makefile

GPPPARAMS = -m32 -fno-use-cxa-atexit -nostdlib -fno-builtin -fno-rtti -fno-exceptions -fno-leading-underscore
ASPARAMS = --32
LDPARAMS = -melf_i386

objects = loader.o kernel.o

%.o: %.cpp
    g++ $(GPPPARAMS) -o $@ -c $<

%.o: %.s
    as $(ASPARAMS) -o $@ $<
    
mykernel.bin: linker.ld $(objects)
    ld $(LDPARAMS) -T $< -o $@ $(objects) 

install: mykernel.bin
    sudo cp $< /boot/mykernel.bin

in /boot/grub/grub.cfg, i added:

menuentry 'My kernel' {
    multiboot /boot/mykernel.bin
    boot
}

Thanks in advance and have my excuses if I didn't write my question clear enough.

Answer 1

Solution: It only works under MBR/CSM legacy configurations and I found out that all the computers which I tried were UEFI/GPT. Now I do not know how to make it compatible for UEFI/GPT, but if I cannot that's fine, I could not find anything on the internet. It works under Virtualbox, after replacing 0F00 instead of FF00 as it was also writing black on black. (check comments for more details)