Memory map and Framebuffer after using ExitBootServices - 64-bit

Question

I guess the question is pretty straight forward itself.
Is there any way of detecting the memory (or getting he memory map) and framebuffer (or Graphics Output Protocol) after using ExitBootServices in UEFI in 64-bit mode? If so then how and is there any documentation?
I know that after using ExitBootServices, you the the sole owner of the entire machine.
There are many ways of getting the memory map but they all take help of the bootloader. I want to get the memory map directly from the kernel. Many websites such as OSDev and github sources use bootloaders to get the memory map and framebuffer.
After using ExitBootServices, I'm left in 64-bit mode and the only page on OSDev wiki about getting the memory map works on 32-bit architecture.
I have no language preferences, it may be in C, assembly or whatever and please don't say that it's useless or complicated or difficult to do. I just want an answer.

Answer 1

First, (Probably in (U)EFI) U cannot call boot services which is the only way to get what you want, you can get the memory map & Frame Buffer before ExitBootServices() and pass them to the kernel, you're lucky cause I'm not always on this platform, I've a Hybrid Boot Mechanism with LEGACY BIOS & UEFI Support, and here is an example of how to do that (I'm working on EDK2 Which is the Official Implementation of EFI)
This is how you get the frame buffer from G.O.P ( UGA documentation is removed ):
FRAME_BUFFER_DESCRIPTOR* GraphicsOutputProtocolInitialize(){
// First, we need to query the firmware of all G.O.P Protocol Instances
// (Each instance may represent a GPU or a monitor, GOP features multiple-screens
// U have asked for a simple implementation so we will use only 1 frame buffer
EFI_STATUS status = 0;
EFI_HANDLE* HandleBuffer = NULL;
UINTN NumProtocolHandles = 0;
if(EFI_ERROR(gBS->LocateHandleBuffer(
ByProtocol, &gEfiGraphicsOutputProtocolGuid, NULL,
&NumProtocolHandles, &HandleBuffer
)) || !NumProtocolHandles) return NULL;
// Then u need to create a structure that you can pass to the kernel containing information about frame buffers
FRAME_BUFFER_DESCRIPTOR* FrameBuffer = NULL;
if(EFI_ERROR(gBS->AllocatePool(
EfiLoaderData, sizeof(FRAME_BUFFER_DESCRIPTOR), (void**)&FrameBuffer
))) ALLOCATION_PROBLEM;
ZeroMemory((void*)FrameBuffer, sizeof(FRAME_BUFFER_DESCRIPTOR));
EFI_GRAPHICS_OUTPUT_PROTOCOL* gop = NULL;
status = gBS->OpenProtocol(
HandleBuffer[0], // Get first Graphics Output Protocol Instance
&gEfiGraphicsOutputProtocolGuid,
(void**)&gop,
NULL,
NULL,
EFI_OPEN_PROTOCOL_GET_PROTOCOL
);
if(EFI_ERROR(status) || !gop)
{
return NULL;
}
EFI_GRAPHICS_OUTPUT_MODE_INFORMATION* ginfo = NULL;
UINTN info_size = 0;
// if mode is not yet set by firmware, then set first mode
if(status == EFI_NOT_STARTED || !gop->Mode){
status = gop->SetMode(gop, 0);
if(EFI_ERROR(status) || !gop->Mode->Mode)
{
return NULL;
}
}
// Now we will ask firmware for the current Video Mode
status = gop->QueryMode(gop, gop->Mode->Mode, &info_size, &ginfo);
if(status != EFI_SUCCESS || !ginfo){
return NULL;
}
// You can also list availaible video modes
for(UINTN i = 0;i<gop->Mode->MaxMode;i++) {
status = gop->QueryMode(gop, i, &info_size, &ginfo);
if(status != EFI_SUCCESS || !ginfo){
return NULL;
}
// To set the mode :
status = gop->SetMode(gop, i);
if(EFI_ERROR(status))
{
return NULL;
}
}
FrameBuffer->FrameBufferSize = gop->Mode->FrameBufferSize;
FrameBuffer->HorizontalResolution = gop->Mode->Info->HorizontalResolution;
FrameBuffer->VerticalResolution = gop->Mode->Info->VerticalResolution;
FrameBuffer->FrameBufferBase = (char*)gop->Mode->FrameBufferBase;
ZeroMemory((void*)FrameBuffer, sizeof(FRAME_BUFFER_DESCRIPTOR));
}
return FrameBuffer;
}
This is how you get the memory map :
On the first Call you will get the size of the memory map (Status must be EFI_BUFFER_TOO_SMALL)
Then you add 2 * descriptor size coz there is always 2 additional entries, then you allocate buffer for memory map
On the second call, you will get the actual memory map (Status must be EFI_SUCCESS)
Then u can list memory map entries normally
This is how u make a call to GetMemoryMap() :
EFI_MEMORY_DESCRIPTOR* memory_map = NULL;
UINTN map_size = 0, map_key = 0, descriptor_size = 0;
// Must return EFI_BUFFER_TOO_SMALL on First Call
// map_size will contain buffer size needed
EFI_STATUS s = SystemTable->BootServices->GetMemoryMap(&map_size,memory_map,&map_key,&descriptor_size,&descriptor_version);
map_size+=2*descriptor_size; // this padding must be added since there is 2 additionnal entries
However, u can always ask for a code sample, the previous code of (G.O.P) is just copy-pasted and modified to make it a little bit easier to understand, it is not compiled so it may contain some faults.