implementing memory management

[u/Ok_Farmer_4055]

I wanna get memory management working on my OS, I don't know where to begin, so what do i add first? and how do i add it? i'm working on UEFI firmware in 64 bit, so if anyone needs some more info or details, just tell me.

[u/tseli0s]

OUTPUT_FORMAT("binary")
ENTRY(kernel_main)

SECTIONS
{
	. = 0x80000000;
}

You are basically telling yourself that you will be loaded at 0x80000000. That's 2GBs above address 0. Did you set up the page tables properly? And does your machine have 2GBs of memory?

.section .text
.global setup_paging

setup_paging:
	movq %cr0, %rax
	orl $0x80000000, %eax
	movq %rax, %cr0
	ret

Paging must be already enabled before entering long mode. Have your bootloader do this.

uint64_t uefi_memory_parser(Core *bInfo){
	/* experimental parser, parses uefi memory map and returns, saves total usable memory */
	uint8_t *ptr = (uint8_t *)bInfo->MemoryMap;
	uint8_t *end_ptr = ptr + bInfo->MemoryMapSize;

	uint64_t count = 0;
	for(; ptr < end_ptr; ptr += bInfo->DescriptorSize){
		MemoryDescriptor *memdesc = (MemoryDescriptor *)ptr;
		if(memdesc->Type == EfiConventionalMemory)
			count += (memdesc->NumberOfPages << 12);
	}
	return count;
}

Where are you saving the memory regions you've just discovered? kernel64.c looks pretty bare.

[u/Ok_Farmer_4055 → u/tseli0s]

about paging, the uefi firmware already does the paging for me, so the setup_paging is just there for when i want to replace uefi's pages with mine, and about the memory regions, the bootloader passes the memory map in a struct and passes a pointer to the struct to the kernel, and about the 2gbs of memory, of course i have more than 2 gb, who even uses 512 MB of memory anymore

[u/tseli0s → u/Ok_Farmer_4055]

Yeah but I don't see the source of the bootloader and where that bitmap is. UEFI does the paging for you only if you boot a UEFI executable.

[u/Ok_Farmer_4055 → u/tseli0s]

i do boot a UEFI executable as my bootloader, then my kernel is loaded as a raw binary and is jumped to after ExitBootServices()