feat: aarch64 port - fix build system obstacles, add exception handling, page tables

GNUmakefile

@@ -10,6 +10,22 @@ QEMUFLAGS := -smp 4 -m 2G -d int -D qemu.log -no-reboot
 
 override IMAGE_NAME := montauk-$(ARCH)
 
+# Userspace exists only for x86_64 so far: other architectures get a
+# ramdisk holding just the boot files.
+ifeq ($(ARCH),x86_64)
+    KERNEL_ONLY ?= 0
+else
+    KERNEL_ONLY ?= 1
+endif
+
+override EFI_LOADER_x86_64 := BOOTX64.EFI
+override EFI_LOADER_aarch64 := BOOTAA64.EFI
+override EFI_LOADER_riscv64 := BOOTRISCV64.EFI
+override EFI_LOADER_loongarch64 := BOOTLOONGARCH64.EFI
+
+# AArch64 UEFI firmware for QEMU (Debian/Ubuntu: qemu-efi-aarch64).
+AARCH64_EFI_FIRMWARE ?= /usr/share/qemu-efi-aarch64/QEMU_EFI.fd
+
 # Toolchain for building the 'limine' executable for the host.
 HOST_CC := cc
 HOST_CFLAGS := -g -O2 -pipe
@@ -51,29 +67,34 @@ run-hdd-x86_64: $(IMAGE_NAME).hdd
 		$(QEMUFLAGS)
 
 .PHONY: run-aarch64
+# The machine mirrors the Raspberry Pi 4/400: Cortex-A72 cores and a GICv2.
+# The kernel console is mirrored to the PL011 (-serial stdio).
 run-aarch64: $(IMAGE_NAME).iso
 	qemu-system-$(ARCH) \
-		-M virt \
+		-M virt,gic-version=2 \
 		-cpu cortex-a72 \
 		-device ramfb \
 		-device qemu-xhci,id=xhci \
 		-device usb-kbd,bus=xhci.0 \
 		-device usb-mouse,bus=xhci.0 \
-		-bios /usr/share/ovmf/OVMF.fd \
+		-bios $(AARCH64_EFI_FIRMWARE) \
 		-cdrom $(IMAGE_NAME).iso \
+		-serial stdio \
 		$(QEMUFLAGS)
 
 .PHONY: run-hdd-aarch64
 run-hdd-aarch64: $(IMAGE_NAME).hdd
 	qemu-system-$(ARCH) \
-		-M virt \
+		-M virt,gic-version=2 \
 		-cpu cortex-a72 \
 		-device ramfb \
 		-device qemu-xhci,id=xhci \
 		-device usb-kbd,bus=xhci.0 \
 		-device usb-mouse,bus=xhci.0 \
-		-bios /usr/share/ovmf/OVMF.fd \
-		-hda $(IMAGE_NAME).hdd \
+		-bios $(AARCH64_EFI_FIRMWARE) \
+		-drive if=none,id=hd0,format=raw,file=$(IMAGE_NAME).hdd \
+		-device virtio-blk-pci,drive=hd0 \
+		-serial stdio \
 		$(QEMUFLAGS)
 
 .PHONY: run-riscv64
@@ -196,13 +217,23 @@ ports: programs
 	fi
 
 .PHONY: ramdisk
+ifeq ($(KERNEL_ONLY),1)
+ramdisk: limine/limine kernel
+	rm -rf .kernel-only-root
+	mkdir -p .kernel-only-root/boot/limine
+	cp -v limine/$(EFI_LOADER_$(ARCH)) limine.conf .kernel-only-root/boot/limine/
+	cp -v kernel/bin-$(ARCH)/kernel .kernel-only-root/boot/
+	./scripts/mkramdisk.sh .kernel-only-root ramdisk.tar
+	rm -rf .kernel-only-root
+else
 ramdisk: limine/limine kernel programs
 	mkdir -p programs/bin/boot/limine
-	cp -v limine/BOOTX64.EFI programs/bin/boot/limine/
+	cp -v limine/$(EFI_LOADER_$(ARCH)) programs/bin/boot/limine/
 	cp -v limine.conf programs/bin/boot/limine/
 	cp -v kernel/bin-$(ARCH)/kernel programs/bin/boot/
 	rm -f programs/bin/boot/ramdisk.tar
 	./scripts/mkramdisk.sh programs/bin ramdisk.tar
+endif
 
 $(IMAGE_NAME).iso: limine/limine kernel ramdisk
 	rm -rf iso_root