osdev

How do I perform an indirect far jump/call in protected mode? First I was thinking that doing this is allowable: jmp 0x10:eax; (Don't worry about the segment selector..the 2nd entry of my GDT is a valid code segment) But when nasm assembled it, it was a syntax error. Looking at the Book 2a of the Intel (instruction set reference) manual, it can only be done using jmp ptr16:32 , where the ptr16:32 is an immediate value, or using jmp m16:32 , where the m16:32 is a memory location containing the 48-bit jump address (the 16:32). Now I tried to encode it this way: mov dword[ds:jumpaddress_offset]

I'm developing a boot loader, which will boot into a simple kernel after switching into protected mode. I used this paper as a tutorial, somewhere in chapter four or five. In theory it is supposed to start in 16-bit real mode, load the kernel into memory, switch to 32-bit protected mode and start executing the kernel code. However, when I switch into protected mode and far jump or jump to another segment, it triple faults. Here is the main boot sector code: [org 0x7c00] KERNEL_OFFSET equ 0x1000 mov [BOOT_DRIVE], dl ;Get the current boot drive from the BIOS mov bp, 0x9000 ;Set up stack, with

I'm trying to write an extremely simple MBR to start learning how to write an MBR/Kernel. This is what I have so far (created from pieces of other MBRs). The binary I get from using nasm and then ld to link is a bit different from just using nasm for both, but that doesn't appear to be the problem. I first started with jmp 0:continue but that appears to jump to 0000:7c22 (or 001d with nasm alone... i believe i didnt specify that it starts at 7c00 ) but im looking to jump to :7a22 or :7a1d , the address of the relocated code. I tried using just jmp continue and then as seen uncommented below,

I was engaged with an expert who allegedly has vastly superior coding skills than myself who understands inline assembly far better than I ever could. One of the claims is that as long as an operand appears as an input constraint, you don't need to list it as a clobber or specify that the register has been potentially modified by the inline assembly. The conversation came about when someone else was trying to get assistance on a memset implementation that was effectively coded this way: void *memset(void *dest, int value, size_t count) { asm volatile ("cld; rep stosb" :: "D"(dest), "c"(count),

I am writing a tiny OS as part of an assigment for school,but I got stuck when it comes to get keyboard input (press a key -> display it on screen). I am using the Bare Bones tutorial from osdev.org (gcc cross-compiler, GRUB bootloader, ld linker) and since I am in protected mode I can not use BIOS interrupts for input, that's why I have to write my own interrupt handler (?) but I'm not sure how to do that even after I read some osdev articles and forum discussions. Very similar problem ( http://forum.osdev.org/viewtopic.php?f=1&t=9746 ) except that I don't know how to "set up the interrupts".

I am learning Operating system tutorials. I created 2 files. boot.asm kernel.c The kernel.c is as follows : int main() { char *src = (char *)0xB8000000L; *src = 'M'; src += 2; *src = 'D'; return 0; } The kernel is used to write a character to the text mode video display area. The kernel was compiled using Windows version of GCC with: gcc -ffreestanding -c -m16 kernel.c -o kernel.o I link the kernel object to a binary file using LD : ld -Ttext 0x10000 --oformat binary -o kernel.bin kernel.o The error I get is: ld : cannot link the file which is not PE executable type Can anybody solve this

I have developed a basic kernel in assembly/c that runs a basic terminal. I have set it up to run off of an iso with grub. I would like to continue this OS, but without a file system, I feel as if there's really nothing else I could do. After much time on the internet, I have come up with really nothing I can do to implement this. People have said implement FAT or make a VFS, but nothing any further, nor tutorials, nor any references to anywhere. Could someone explain how a file system works, where I can get started/where I can connect a pre-made system, and how to use it? Also, I do not have

I am trying to make a simple kernel using C. Everything loads and works fine, and I can access the video memory and display characters, but when i try to implement a simple puts function for some reason it doesn't work. I've tried my own code and other's. Also, when I try to use a variable which is declared outside a function it doesn't seem to work. This is my own code: #define PUTCH(C, X) pos = putc(C, X, pos) #define PUTSTR(C, X) pos = puts(C, X, pos) int putc(char c, char color, int spos) { volatile char *vidmem = (volatile char*)(0xB8000); if (c == '\n') { spos += (160-(spos % 160)); }