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When I write code works fine.

but when I do this Instead of printing 'X' it prints ' '(blank space/ deletes character that's already there)

Here's my full code:

https://github.com/Optimizer0/IAOS

Is this in protected mode? If so, could you share your gdt. -snip dumb misreading-

Yes this is protected mode.

Here's my gdt. yeah but I can't use char to send strings can I?

Thank you.

I'd offer you the same advice as before, but you'd only ignore it so there's no point.

You're not showing us enough of your code for a sensible answer - link to your repository.

Optimizer wrote:When I write

Code: Select all

void main()
{
 print("");
}
void print(char* message)
{
 char c = 'X';
 char* vga = (char*)0xb8000;
 vga[offset] = c;
 vga[offset+1] = 0x0f;
}

code works fine.

but when I do this

Code: Select all

void main()
{
 print("X");
}

void print(char* message)
{
 char c = message[0];
 char* vga = (char*)0xb8000;
 vga[offset] = c;
 vga[offset+1] = 0x0f;
}

Instead of printing 'X' it prints ' '(blank space/ deletes character that's already there)

Maybe because you're passing an string instead of a character... (change char* message to char message, and instead of "X" use 'X') I don't know, we don't have enough info.

Optimizer wrote:When I write

Code: Select all

void main()
{
 print("");
}
void print(char* message)
{
 char c = 'X';
 char* vga = (char*)0xb8000;
 vga[offset] = c;
 vga[offset+1] = 0x0f;
}

code works fine.

but when I do this

Code: Select all

void main()
{
 print("X");
}

void print(char* message)
{
 char c = message[0];
 char* vga = (char*)0xb8000;
 vga[offset] = c;
 vga[offset+1] = 0x0f;
}

Instead of printing 'X' it prints ' '(blank space/ deletes character that's already there)

Maybe because you're passing an string instead of a character... (change char* message to char message, and instead of "X" use 'X') I don't know, we don't have enough info.

iansjack wrote:I'd offer you the same advice as before, but you'd only ignore it so there's no point.

You're not showing us enough of your code for a sensible answer - link to your repository.

Sir I didn't ignore your last message. I didn't debug right now because I couldn't get the gdb and qemu working. I didn't worry about this much cause I'm soon switching to linux.

I'm a beginner to this and by your stars I know you are far more experienced than me and I know what you say is important.

Here's my repo.
https://github.com/Optimizer0/IAOS

hextakatt wrote:

Optimizer wrote:When I write

Code: Select all

void main()
{
 print("");
}
void print(char* message)
{
 char c = 'X';
 char* vga = (char*)0xb8000;
 vga[offset] = c;
 vga[offset+1] = 0x0f;
}

code works fine.

but when I do this

Code: Select all

void main()
{
 print("X");
}

void print(char* message)
{
 char c = message[0];
 char* vga = (char*)0xb8000;
 vga[offset] = c;
 vga[offset+1] = 0x0f;
}

Instead of printing 'X' it prints ' '(blank space/ deletes character that's already there)

Maybe because you're passing an string instead of a character... (change char* message to char message, and instead of "X" use 'X') I don't know, we don't have enough info.

It will work fine but I want pass strings

Are you sure you are loading enough sectors from the disk?

Optimizer wrote:

iansjack wrote:I'd offer you the same advice as before, but you'd only ignore it so there's no point.

You're not showing us enough of your code for a sensible answer - link to your repository.

Sir I didn't ignore your last message. I didn't debug right now because I couldn't get the gdb and qemu working. I didn't worry about this much cause I'm soon switching to linux.

I'm a beginner to this and by your stars I know you are far more experienced than me and I know what you say is important.

Here's my repo.
https://github.com/Optimizer0/IAOS

1- Open qemu with the -s and -S flag
2- Open GDB and type target remote localhost:1234

Are you linking in a section called ".rodata"? It belongs just past the .text section. It's where all the strings are stored.

This is only a possible guess:

You aren't use a cross compiler. If the OS you are building on is 64-bit then it is likely generating 64-bit code. GCC will need the -m32 option and LD will need the option -melf_i386 added to them to generate and link 32-bit code. This is a guess based on similar problems with video output working inconsistently as you describe are often related to 64-bit code running in 32-bit protected mode. It won't work as expected. If this is your problem then I rote a Stackoverflow answer about something similar: https://stackoverflow.com/questions/398 ... y/39815993
If building 32bit kernels I recommend using an i686 (or i386) cross compiler. OSDev Wiki has information on doing that: https://wiki.osdev.org/GCC_Cross-Compiler
I see you are using Windows. If you are using a 64-bit toolchain you might have to use -mi386pe with LD.

I won't delete this but it appears this likely isn't your problem.

nullplan wrote:Are you linking in a section called ".rodata"? It belongs just past the .text section. It's where all the strings are stored.

Since he seems to be using a Windows GCC compiler(and not a cross compiler) he might need to use *(.rdata*)in the liner script.

I learned you were using MingGW 6.3.0 and Nullplan'ss general observation about the read only data section appears correct, except with MinGW the read only data sections are .rdata*. Try modifying your linker script to look like:I also amended it to be *(.text*) as it is possible for GCC to create a number of .text sections that begin with .text.

It really is a symptom though that you are only reading 2 sectors in boot.asm. The default alignment with the MinGW linker is 4kb for sections that don't explicitly appear in the linker script. Your read only data happens to sit outside the sectors of the disk you did read so the memory where your string would have been was probably filled with zeros. Setting AL to 17 for int13h/ah=2 would be a start but hard coding the size is a hack.

hextakatt wrote:

Optimizer wrote:

iansjack wrote:I'd offer you the same advice as before, but you'd only ignore it so there's no point.

You're not showing us enough of your code for a sensible answer - link to your repository.

Sir I didn't ignore your last message. I didn't debug right now because I couldn't get the gdb and qemu working. I didn't worry about this much cause I'm soon switching to linux.

I'm a beginner to this and by your stars I know you are far more experienced than me and I know what you say is important.

Here's my repo.
https://github.com/Optimizer0/IAOS

1- Open qemu with the -s and -S flag
2- Open GDB and type target remote localhost:1234

I tried it but when I type commands like "continue" gdb says invalid remote reply