35fad84fec
1 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
Roger Pau Monné
|
ca49b3342d |
loader: implement multiboot support for Xen Dom0
Implement a subset of the multiboot specification in order to boot Xen and a FreeBSD Dom0 from the FreeBSD bootloader. This multiboot implementation is tailored to boot Xen and FreeBSD Dom0, and it will most surely fail to boot any other multiboot compilant kernel. In order to detect and boot the Xen microkernel, two new file formats are added to the bootloader, multiboot and multiboot_obj. Multiboot support must be tested before regular ELF support, since Xen is a multiboot kernel that also uses ELF. After a multiboot kernel is detected, all the other loaded kernels/modules are parsed by the multiboot_obj format. The layout of the loaded objects in memory is the following; first the Xen kernel is loaded as a 32bit ELF into memory (Xen will switch to long mode by itself), after that the FreeBSD kernel is loaded as a RAW file (Xen will parse and load it using it's internal ELF loader), and finally the metadata and the modules are loaded using the native FreeBSD way. After everything is loaded we jump into Xen's entry point using a small trampoline. The order of the multiboot modules passed to Xen is the following, the first module is the RAW FreeBSD kernel, and the second module is the metadata and the FreeBSD modules. Since Xen will relocate the memory position of the second multiboot module (the one that contains the metadata and native FreeBSD modules), we need to stash the original modulep address inside of the metadata itself in order to recalculate its position once booted. This also means the metadata must come before the loaded modules, so after loading the FreeBSD kernel a portion of memory is reserved in order to place the metadata before booting. In order to tell the loader to boot Xen and then the FreeBSD kernel the following has to be added to the /boot/loader.conf file: xen_cmdline="dom0_mem=1024M dom0_max_vcpus=2 dom0pvh=1 console=com1,vga" xen_kernel="/boot/xen" The first argument contains the command line that will be passed to the Xen kernel, while the second argument is the path to the Xen kernel itself. This can also be done manually from the loader command line, by for example typing the following set of commands: OK unload OK load /boot/xen dom0_mem=1024M dom0_max_vcpus=2 dom0pvh=1 console=com1,vga OK load kernel OK load zfs OK load if_tap OK load ... OK boot Sponsored by: Citrix Systems R&D Reviewed by: jhb Differential Revision: https://reviews.freebsd.org/D517 For the Forth bits: Submitted by: Julien Grall <julien.grall AT citrix.com> |