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== Supported Platforms ==
* Legacy BIOS (x86_64 with PMBR)▼
* El Torito "no emulation" CDROM boot (x86_64)▼
* UEFI (x86_64)▼
* Raspberry Pi (AArch64)
* Legacy BIOS boot with any arbitrary boot manager (x86_64, chainloaded from VBR)
* Legacy BIOS boot with a single OS on a forward-compatible GPT disk (x86_64, booted from PMBR)
* Legacy BIOS for embedded systems (x86_64, in BIOS Expansion ROM)
▲* UEFI (x86_64)
* UEFI for embedded systems (x86_64, in PCI Option ROM)
* CDROM, El Torito UEFI boot Extension (x86_64)
* ISOLINUX / LILO / BOOTLIN / etc. (x86_64 via the Linux kernel boot protocol)
* COREBOOT: as a primary payload in ROM (x86_64)
For GRUB compatibility, BOOTBOOT is also Multiboot compliant, so you can add it to the grub.cfg in it's own entry. This is useful if want to dual boot multiple OSes.
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== Supported Sources ==
Your kernel can be wrapped in an initial ramdisk archive ([[USTAR]], cpio, James Molloy's initrd format etc.), which in turn can be a simple file on a [[FAT|FAT16/32]] partition; or can occupy the whole partition as well using a file system of your choosing ([[SFS]] among others). BOOTBOOT uses GPT partitions, so your boot partition should be either an [[EFI_System_Partition|ESP]], or it should have the bootable flag (attribute 2) set.
If despite the warning you decide to [[Roll Your Own Filesystem]], then BOOTBOOT is definitely for you. You can either write an FS module (one function), or just make sure the kernel is the first executable in the archive / on the partition. BOOTBOOT is capable of loading kernels from unknown file systems as well.
Optionally you can load your OS from ROM (see qemu's -option-rom command line argument, or bochs rc file; or with [https://coreboot.org coreboot] as a BIOS using qemu -bios), and the Raspberry Pi version can also load the ramdisk over serial line. Although it's not implemented as of yet, the BOOTBOOT protocol allows loading the initrd from a TFTP server.
== Your Kernel ==
You can use ELF64 or PE32+ formats for your kernel. You must link it as a [[Higher Half Kernel]], and your entry point should point to [[Long Mode]] code. That's all. Unlike all the other boot protocols (e.g. [[Multiboot]] and [[stivale]]), there's absolutely no need for special sections nor for magic structs, unimplementable in some languages. No real mode nor protected mode trampoline code needed
BOOTBOOT passes a configuration to your kernel in a newline separated, zero-terminated UTF-8 string. Each line contains a ''key=value'' pair, where only two keys, "screen" and "kernel" are reserved. You are free to use any other keys that your kernel wishes to use.
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== Console ==
BOOTBOOT does not support VGA text mode, it sets up graphic mode regardless to the platform. You don't have to mess around with [[VESA]] or [[GOP]] any more, you will get the frame buffer ready to use. The example Hello World kernel provided with the BOOTBOOT source has a minimal puts() example, which outputs text on that frame buffer using [[PC Screen Font]] (same that Linux Console uses). You can also use the [[Scalable Screen Font]] library's ''ssfn_putc()''.
The loader also initializes the [[Serial_Ports|serial console]] for you with 115200 baud, 8 data bits, no parity and 1 stop bit. Your kernel can send debug messages from the start.
== How to Install ==
You can install BOOTBOOT yourself following the [[Bootable_Disk|bootable disk]] tutorial and using one of the provided mkboot.c utilities. But the simplest way is to use
the multiplatform (Windows, MacOSX, Linux) disk image creator tool, [https://gitlab.com/bztsrc/bootboot/tree/master/mkbootimg mkbootimg] which is very similar to [[GRUB|grub-mkrescue]].
For input, you provide the contents of your initrd in a directory, and a JSON configuration describing what disk image you would like. The rest is taken care for you.
== There's more... ==
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== External Links ==
*[https://gitlab.com/bztsrc/bootboot Source on Gitlab] the repository
*[https://gitlab.com/bztsrc/bootboot/
*[https://gitlab.com/bztsrc/bootboot/tree/master/mkbootimg mkbootimg] simple to use, dependency-free [[Bootable_Disk|bootable disk]] creator
*[https://gitlab.com/bztsrc/bootboot/tree/master/mykernel Example Hello World Kernels] with Makefile and minimal linker script
*Mykernel in [https://gitlab.com/bztsrc/bootboot/tree/master/mykernel/c C]
*Mykernel in [https://gitlab.com/bztsrc/bootboot/tree/master/mykernel/cpp C++]
*Mykernel in [https://gitlab.com/bztsrc/bootboot/tree/master/mykernel/rust Rust]
*Mykernel in [https://gitlab.com/bztsrc/bootboot/tree/master/mykernel/pas Pascal]
*Mykernel in [https://gitlab.com/bztsrc/bootboot/tree/master/mykernel/ada Ada]
*Mykernel in [https://gitlab.com/bztsrc/bootboot/tree/master/mykernel/go Go]
[[Category:Bootloaders]]
[[Category:ARM]]
[[Category:Raspberry Pi]]
[[Category:x86-64]]
[[Category:UEFI]]
[[de:BOOTBOOT]]
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