Splitting out UEFI bootloader code from kernel

Now the bootloader should be responsible for all initial setup,
loading the kernel, and then handing off to the kernel with
proper data in place.

src/boot/loader.c

@@ -0,0 +1,75 @@
+#include "loader.h"
+#include "utility.h"
+
+static CHAR16 kernel_name[] = KERNEL_FILENAME;
+
+static EFI_STATUS loader_load_file(EFI_FILE_PROTOCOL *root, void **kernel_image, UINT64 *len) {
+	EFI_STATUS status;
+
+	EFI_FILE_PROTOCOL *handle = 0;
+	status = root->Open(root, &handle, kernel_name, EFI_FILE_MODE_READ, 0);
+	CHECK_EFI_STATUS_OR_RETURN(status, "Failed to open kernel file handle");
+
+	EFI_FILE_INFO *info = LibFileInfo(handle);
+    if (info->FileSize == 0)
+        return EFI_NOT_FOUND;
+
+    UINTN count = ((info->FileSize - 1) / 0x1000) + 1;
+    EFI_PHYSICAL_ADDRESS addr = 0x100000; // Try to load the kernel in at 1MiB
+    EFI_MEMORY_TYPE memType = 0xFFFFFFFF;  // Special value to tell the kernel it's here
+    status = ST->BootServices->AllocatePages(AllocateAddress, memType, count, &addr);
+    if (status == EFI_NOT_FOUND) {
+        // couldn't get the address we wanted, try loading the kernel anywhere
+        status = ST->BootServices->AllocatePages(AllocateAnyPages, memType, count, &addr);
+    }
+	CHECK_EFI_STATUS_OR_RETURN(status, "Failed to allocate kernel pages");
+
+    UINTN buffer_size = count * 0x1000;
+    void *buffer = (void*)addr;
+    status = handle->Read(handle, &buffer_size, &buffer);
+	CHECK_EFI_STATUS_OR_RETURN(status, "Failed to read kernel to memory");
+
+	*len = buffer_size;
+	*kernel_image = buffer;
+	return EFI_SUCCESS;
+}
+
+EFI_STATUS loader_load_kernel(void **kernel_image, UINT64 *len) {
+    if (kernel_image == 0 || len == 0)
+        CHECK_EFI_STATUS_OR_RETURN(EFI_INVALID_PARAMETER, "NULL kernel_image pointer or size");
+
+	EFI_STATUS status;
+
+	// First, find all the handles that support the filesystem protocol. Call
+	UINTN size = 0;
+	EFI_GUID fs_guid = EFI_SIMPLE_FILE_SYSTEM_PROTOCOL_GUID;
+	status = ST->BootServices->LocateHandle(ByProtocol, &fs_guid, NULL, &size, NULL);
+	if (status != EFI_BUFFER_TOO_SMALL) {
+		CHECK_EFI_STATUS_OR_RETURN(status, "Failed to find number of filesystem handles");
+	} else if (size == 0) {
+		CHECK_EFI_STATUS_OR_RETURN(EFI_NO_MEDIA, "Found zero filesystem handles");
+	}
+
+	EFI_HANDLE *buffer = 0;
+    status = ST->BootServices->AllocatePool(EfiLoaderData, size, (void**)&buffer);
+	CHECK_EFI_STATUS_OR_RETURN(status, "Failed to allocate buffer of filesystem handles");
+
+	status = ST->BootServices->LocateHandle(ByProtocol, &fs_guid, NULL, &size, buffer);
+	CHECK_EFI_STATUS_OR_RETURN(status, "Failed to find filesystem handles");
+
+	unsigned num_fs = size / sizeof(EFI_HANDLE);
+	EFI_HANDLE *fss = (EFI_HANDLE*)buffer;
+
+	for (unsigned i = 0; i < num_fs; ++i) {
+		EFI_FILE_HANDLE root = LibOpenRoot(fss[i]);
+
+		status = loader_load_file(root, kernel_image, len);
+        if (status == EFI_NOT_FOUND)
+            continue;
+
+		CHECK_EFI_STATUS_OR_RETURN(status, "Failed to load kernel");
+        return EFI_SUCCESS;
+	}
+
+    return EFI_NOT_FOUND;
+}