adds some comments, fixes a few tiny bugs

This commit is contained in:
2025-05-31 20:50:47 -04:00
parent c50d3f14a6
commit 89c02d6a93
3 changed files with 56 additions and 8 deletions

View File

@ -1,3 +1,7 @@
; Here is our entry point to the kernel
; A very simple assembly file
; We set up some parameters and then pass the execution to our kmain
global loader ; entry symbol for ELF
extern kmain
@ -6,12 +10,17 @@ FLAGS equ 0x3
CHECKSUM equ -(MAGIC_NUMBER + FLAGS) ; calculate the checksum
KERNEL_STACK_SIZE equ 4096
; The multiboot section is a semi requirement for grub
; All this is doing is placing the required magic number, flags, and the checksum into the file first
; This lets grub know if this is a valid multiboot kernel or not
section .multiboot
align 4 ; code must be 4 byte aligned
dd MAGIC_NUMBER
dd FLAGS
dd CHECKSUM
; Here we're setting up the stack
; Giving us 4096 bytes (resb)
section .bss
align 4
kernel_stack:
@ -19,10 +28,12 @@ kernel_stack:
section .text
loader:
mov esp, kernel_stack + KERNEL_STACK_SIZE
mov esp, kernel_stack + KERNEL_STACK_SIZE ; move the top of the stack into esp
call kmain
call kmain ; pass execution over to our kmain function, where all of the real stuff is done
;cli
; Should the system exit, we clear the interrupt flag
; and do an infinite loop of nothing
cli
loop: hlt
jmp loop

View File

@ -6,6 +6,25 @@
#include <kernel/_kernel.h>
#endif
/**
* What is this file?
*
* Well, to properly set up a lot of the system, we need something called a GDT
* or, a Global Descriptor Table.
*
* This table, establishes a few things.
*
* Mainly it sets 4 segments,
* A kernel code segment, with RING 0 permissions
* A kernel data segment, with RING 0 permissions
* A user code segment, with RING 3 permissions
* A user data segment, with RING 3 permissions
*
* This allows for future userspace to properly segment code and data,
* anything in userspace shouldn't have access to hardware like the kernel does
* So by passing through this GDT, we can dish out authority to access certain data, functions,
* etc, by going through the CPU permission system (RING 0 - 3)
*/
uint64_t gdt[GDT_SIZE];
@ -26,12 +45,14 @@ uint64_t create_descriptor(uint32_t base, uint32_t limit, uint16_t flag)
return descriptor;
}
#ifdef __TESTING__
void dump_gdt(void)
{
for (int i = 0; i < GDT_SIZE; i++) {
printf("GDT_ENTRY %d: %4 | %2\n", i, gdt[i], gdt[i]);
}
}
#endif
void gdt_init(void)

View File

@ -1,25 +1,41 @@
ENTRY(loader)
/**
* This is the linker file.
*
* This file tells the linker (ld) how we want to arrange the code into the output file.
*/
ENTRY(loader) /* This is the first entry point, defined in boot.s */
SECTIONS
{
. = 1M;
/*
* This is telling the linker that anything after here should be loaded at 2M onwards
* The reason for 2M, is that we want to give room for the BIOS, (and UEFI), 2M is generally regarded as a safe spot
* to place the memory offset
* */
. = 2M;
.text BLOCK(4K) : ALIGN(4K)
/*
* BLOCK is an alias for ALIGN, we're telling the linker that we want each section to be aligned at 4K
*/
.text BLOCK(4K) : ALIGN(4K) /* The first section we want is the text section, this is where most code is */
{
*(.multiboot)
*(.text)
*(.multiboot) /* Multiboot needs to be early in the file, required by grub */
*(.text) /* The text section */
}
/* R/O data */
.rodata BLOCK(4K) : ALIGN(4K)
{
*(.rodata)
}
/* Data */
.data BLOCK(4K) : ALIGN(4K)
{
*(.data)
}
/* BSS */
.bss BLOCK(4K) : ALIGN(4K)
{
*(COMMON)