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	int pid = sys_fork();
	//block child as we wipe its page directory
	//strictly for prototyping
	block_task(task_with_pid(pid), ZOMBIE);
	if (!pid) {
		//asm stub which places arg in ebx and calls int 0x80 (syscall vector)
		sys__exit(0xdeadbeef);
	}
	else {
		task_t* child = task_with_pid(pid);
		uint32_t eip_addr = child->eip;
		page_directory_t* old = child->page_dir;

		//for each page table in page directory
		for (int i = 0; i < 1024; i++) {
			page_table_t* tab = old->tables[i];

			//find page table containing this address
			uint32_t instruction_table_idx = (eip_addr / 0x1000) / 1024;
			if (i == instruction_table_idx) {
				//skip clearing page table containing code we want to execute when the child runs
				continue;
			}
			
			//for each page in page table
			for (int j = 0; j < 1024; j++) {
				//skip unassigned pages
				if (!tab->pages[j].frame) continue;

				//many crashes if this is removed
				//don't remove any pages which were linked directly from the kernel
				extern page_directory_t* kernel_directory;
				if (tab->pages[j].frame == kernel_directory->tables[i]->pages[j].frame) {
					continue;
				}
				free_frame(&(tab->pages[j]));
				tab->pages[j].present = 0;
			}
		}
		sleep(3000);
		unblock_task(child);
		int stat;
		waitpid(pid, &stat, NULL);
		printf("Child exited with status %x\n", stat);
		while (1) {}

Code: Select all

		//go through each page table
		for (int i = 0; i < 1024; i++) {
			page_table_t* tab = old->tables[i];

			//if this page table is linked from kernel, make entirely new page table and replace
			if (tab == kernel_directory->tables[i]) {
				uint32_t new_tab_phys;
				page_table_t* new_tab = (page_table_t*)kmalloc_ap(sizeof(page_table_t), &new_tab_phys);
				memset((uint8_t*)new_tab, 0, sizeof(page_table_t));
				old->tables[i] = new_tab;
				old->tablesPhysical[i] = new_tab_phys | 0x07;
				continue;
			}

			printf("clearing non-kernel table @ idx %d\n", i);
			for (int j = 0; j < 1024; j++) {
				if (!tab->pages[j].frame) continue;

				uint32_t vmem_addr = vmem_from_frame(tab->pages[j].frame);
				printf("clearing %x [%x]\n", vmem_addr, tab->pages[j].frame);
				free_frame(&(tab->pages[j]));
				tab->pages[j].present = 0;
			}
		}

		page_t* eip_page = get_page(eip_addr, 1, old);
		printf("eip_page %x\n", eip_page);
		alloc_frame(eip_page, 1, 1);
		page_t* kernel_eip_page = get_page(eip_addr, 0, kernel_directory);

		printf("copying physical data from kernel frame %x to %x\n", kernel_eip_page->frame * 0x1000, eip_page->frame * 0x1000);

		extern void copy_page_physical(uint32_t page, uint32_t dest);
		copy_page_physical(kernel_eip_page->frame * 0x1000, eip_page->frame * 0x1000);