Episode Details

Assembly language on OpenBSD, using bhyve for FreeBSD development, FreeBSD Gaming, FreeBSD for Thanksgiving, no space left on Dragonfly’s hammer2, and more.

##Headlines
###Assembly language on OpenBSD amd64+arm64

This is a short introduction to assembly language programming on OpenBSD/amd64+arm64. Because of security features in the kernel, I have had to rethink a series of tutorials covering Aarch64 assembly language on OpenBSD, and therefore this will serve as a placeholder-cum-reminder.

OpenBSD, like many UNIX and unix-like operating systems, now uses the Executable and Linkable Format (ELF) for its binary libraries and executables. Although the structure of this format is beyond the scope of this short introduction, it is necessary for me to explain part of one of the headers.

Within the program header there are sections known as PT_NOTE that OpenBSD and other systems use to distinguish their ELF executables - OpenBSD looks for this section to check if it should attempt to execute the program or not.

• Our first program: in C!

It’s often a good idea to prototype your assembly programs in a high level language such as C - it can then double up as both a set of notes and a working program that you can debug and compile into assembly language to compare with your own asm code.

• See the article for the rest on:
• Our first program: in x86-64 Asm (AT&T/GAS syntax)
• Our first program: in inline x86-64 assembly
• Our first program: in x86-64 asm (NASM syntax)
• Our first program: in ARMv8 AArch64 assembly

###Using bhyve for FreeBSD Development

• The Hypervisor

The bhyve hypervisor requires a 64-bit x86 processor with hardware support for virtualization. This requirement allows for a simple, clean hypervisor implementation, but it does require a fairly recent
processor. The current hypervisor requires an Intel processor, but there is an active development branch with support for AMD processors.
The hypervisor itself contains both user and kernel components. The kernel driver is contained in the vmm.ko module and can be loaded either at boot from the boot loader or at runtime. It must
be loaded before any guests can be created. When a guest is created, the kernel driver creates a device file in /dev/vmm which is used by the user programs to interact with the guest.
The primary user component is the bhyve(8) program. It constructs the emulated device tree in the guest and provides the implementation for most of the emulated devices. It also calls the kernel driver to execute the guest. Note that the guest always executes inside the driver itself, so guest execution time in the host is counted as system time in the bhyve process.
Currently, bhyve does not provide a system firmware interface to the guest (neither BIOS nor UEFI). Instead, a user program running on the host is used to perform boot time operations including loading the guest operating system kernel into the guest’s memory and setting the initial guest state so that the guest begins execution at the kernel’s entry point. For FreeBSD guests, the bhyveload(8) program can be used to load the kernel and prepare the guest for execution. Support for some other operating systems is available via the grub2-bhyve program which is available via the sysutils/grub2-bhyve port or as a prebuilt package.
The bhyveload(8) program in FreeBSD 10.0 only supports 64-bit guests. Support for 32-bit guests will be included in FreeBSD 10.1.

• See the article for the very technical breakdown of the following: