Ruben Safir ruben at mrbrklyn.com
Thu Sep 23 05:17:41 EDT 2021

On Thu, Sep 23, 2021 at 09:13:02AM +0200, Bjørn Mork wrote:
> Ruben Safir <ruben at mrbrklyn.com> writes:
> > OS's shouldn't need anything from a boot loader.
> Why do you need a bootloader then?

To boot and that is it.  It is a hardware specific ibinary boot chain that
finds the kernal on the hard drive and says - load that and run.

After that, it should serve no purpose.

> I'd suggest playing with embedded devices for a while. Their boot chain
> is usually much simpler than on PC hardware. There you can really get a
> feeling of how easy and decoupled stuff could have been. Load a kernel
> directly to some location in memory and just jump there.

That is pretty much all you want.  Firmware creep has gotten so 
unecesserily complex that UEFI has a virtual machine running in it.

I don't need or want it to play a multiplayer networked version of 
freecell.  I just need it to find the kernel and load it.

> Then try to expand a bit by reading the kernel from some specific flash
> device, or even network.  

Hardware interupts work to announce hardware on the bus.  The devices 
announce themselves on the system bus.

> Maybe trying to make the kernel do the right
> thing depending on where it was booted from.  

No it doesn't unless your hardware is broken.  Why should it?
The kernel responds independently to its hardware environment.
These show up is dmesg.

> Or add a file system to
> the flash.  Etc.  Maybe you even want some way to configure the
> bootloader from the OS?

This wasn't invented with UEFI.  

> Add all the features you take for granted on PC hardware.
> I think you will find that the OS has to be aware of some of the stuff
> the bootloader does.  And that many of the features depend on the OS
> communicating with the bootloader somehow.  

Why?  The Kernel interacts with the hardware independently.  
The devices each have their own firmware and process data
according to an API and the Kernel either natively, or through loaded
modules, processes data from the devices.  There is nothing here for a
boot loader to do.  It ran its bit on the stack and it should be gone.

If you run a system in BIOS mode or even with just a BIOS, the Kernal 
can still do everything, including SATA and Thunderbolt, Firewire,
PCI-Express, SATA etc.

What can it do with UEFI that it can not do with BIOS?

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