… all is forgiven.
ARM booting sucks in several very concrete ways:
- As there is no standard display hardware nor standard serial port, it’s essentially impossible for a random firmware or kernel to output debug messages. (Like text mode + 16550 on a PC). The most likely outcome for the poor developer is a black screen of nothingness. This could be easily fixed if ARM allocated a standard serial port address and put it into every shipping ARM core.
- ARM instruction sets aren’t standardized. There’s no core of instructions that will work on any ARM (compare to 8086 on a PC). So there’s no way to write a bootloader that works everywhere. [For privileged instructions — unprivileged instructions are usually backwards compatible, except when they’re not (Thumb), but that doesn’t help when writing a bootloader.]
- There is a standard bootloader of sorts, or at least one which is very frequently used, called U-Boot. That’s good, but everyone and their uncle modifies it so it’s forked all over the place. And make sure you’ve got the exact fork for your hardware, otherwise you’ll brick it.
- U-Boot is generally bloody confusing, uses a binary blob + special tools for boot configuration, is hard to compile on x86, etc.
- U-Boot may not be replaceable on your hardware, or there may be some other, closed firmware underneath it (hello, R-Pi).
- The hardware isn’t discoverable and self-describing (unlike, say, PCI, USB and every recent PC peripheral). Thus you have Device Trees, big files that describe every piece of hardware, must be written specially for each piece of hardware, and must be correct else you’ll be looking at a black screen of death.
- Kernel signing. No standard toolset for signing kernels. Unfortunately this particular strain of madness is now infecting PCs too.
Anyhow, this explains how I’ve gone from 3 working Fedora ARM systems to 0 in the space of two days.
This is also the reason I think EFI is a terrible mistake. Having now used UEFI a lot more, I think it’s a vast improvement on the ARM bootloader zoo.