figure it out

• (bozo)

TODO

• printing to terminal
• gdt
• idt
• timer interrupts
• keyboard interrupts
• enable paging
• replace nasm with just S cuz why do both lol
• jump to higher half kernel
• virtual memory management kmalloc, kfree, krealloc, kcalloc
  • heap implementation
  • all heap blocks be aligned to 8/16bits? am i bothered? google firstfit vs bestfit
  • add tests for kmalloc kfree
• move tests over to using mrt_test framework. (after malloc implementation)
• bitmap to some other physical memory allocators
• can there be multile regions of free memory to allocate page frames for?
• taskes, schedule(), yield() etc
• time slices for scheduler
• figure out why it when DDEBUG flag is off. why is it trying to run the kernellog command when i say NO WHY
• figure out how to kfree the kmallocs in task.c

TODO implementations

void* vmm_create_new_context(void) purpose: creates a new, blank page map level 4 (pml4) or page directory. logic: allocates a page for the top-level structure. crucially, it must map the kernel into this new context (usually the higher half) so that interrupts work regardless of which task is running.

void vmm_switch_context(void* pml4_phys_addr) purpose: context switching. implementation: on x86, this writes the physical address of the new directory into the cr3 register.

void vmm_destroy_context(void* pml4_phys_addr) purpose: clean up when a task dies. logic: frees the page tables associated with this task (but be careful not to free the kernel's pages!).

void vmm_page_fault_handler(registers_t* regs) purpose: called by the isr (interrupt service routine) when interrupt 14 (on x86) fires. logic: read cr2 (on x86) to find the address that caused the fault. check error code (was it a permission violation? was the page not present?). if valid (e.g., copy-on-write or lazy loading), fix the mapping and return. if invalid (e.g., null pointer dereference), terminate the task.