arm64: Add support for the architecture
This changeset adds basic support to run HelenOS on AArch64, targeting
the QEMU virt platform.
Boot:
- Boot relies on the EDK II firmware, GRUB2 for EFI and the HelenOS
bootloader (UEFI application). EDK II loads GRUB2 from a CD, GRUB2
loads the HelenOS bootloader (via UEFI) which loads OS components.
- UEFI applications use the PE/COFF format and must be relocatable. The
first problem is solved by manually having the PE/COFF headers and
tables written in assembler. The relocatable requirement is addressed
by compiling the code with -fpic and having the bootloader relocate
itself at its startup.
Kernel:
- Kernel code for AArch64 consists mostly of stubbing out various
architecture-specific hooks: virtual memory management, interrupt and
exception handling, context switching (including FPU lazy switching),
support for virtual timer, atomic sequences and barriers, cache and
TLB maintenance, thread and process initialization.
- The patch adds a kernel driver for GICv2 (interrupt controller).
- The PL011 kernel driver is extended to allow userspace to take
ownership of the console.
- The current code is not able to dynamically obtain information about
available devices on the underlying machine. The port instead
implements a machine-func interface similar to the one implemented by
arm32. It defines a machine for the QEMU AArch64 virt platform. The
configuration (device addresses and IRQ numbers) is then baked into
the machine definition.
User space:
- Uspace code for AArch64 similarly mostly implements
architecture-specific hooks: context saving/restoring, syscall
support, TLS support.
The patchset allows to boot the system but user interaction with the OS
is not yet possible.
