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The Linux Boot Process: From Power Button to Kernel

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Re: The Linux Boot Process: From Power Button to Kernel

#11

Post by megous »

superkuh wrote: post #4

Video device initialization is intimately intertwined and a dependency for all this early boot stuff. I was hoping to learn more but it's not even mentioned. Still, neat.

It's not a dependency for Linux boot at all. You can do well with serial port alone, as anyone who brought up eg. an ARM SoC in Linux will attest to.

Also it's not very interesting either. At simplest, Linux just needs to take a pointer to a beginning of a framebuffer and some metadata, and will write to the framebuffer whenever there's something to update.

Re: The Linux Boot Process: From Power Button to Kernel

#13

Post by superkuh »

megous wrote: post #11
superkuh wrote: post #4

Video device initialization is intimately intertwined and a dependency for all this early boot stuff. I was hoping to learn more but it's not even mentioned. Still, neat.

It's not a dependency for Linux boot at all. You can do well with serial port alone, as anyone who brought up eg. an ARM SoC in Linux will attest to. Also it's not very interesting either. At simplest, Linux just needs to take a pointer to a beginning of a framebuffer and some metadata, and will write to the framebuffer whenever there's something to update.

Maybe not linux specifically, but POST requires a video device software (BIOS Option ROM or UEFI GOP Drivers) of some sort does it not? That's been my experience with all PCs for 30 years. But maybe there are cases where it doesn't?

edit: Apparently it's a desktop motherboard firmware thing. Ubiquitous but not technically a requirement for POSTing a computer.

Re: The Linux Boot Process: From Power Button to Kernel

#15

Post by kuekacang »

hamasho wrote: post #14

Funny how those three posts are in hacker news top 5 now. I guess today is the low level appreciation day. * The Linux Boot Process: From Power Button to Kernel * The Journey Before main() * How programs get run: ELF binaries (2015) (lwn.net) edit: format

Oh hey, a fellow noticing person!

Re: The Linux Boot Process: From Power Button to Kernel

#16

Post by nickelpro »

UEFI is an interface implemented by firmware (literally, Unified Extensible Firmware Interface), it's not the firmware itself. Saying "it starts the machine" is a bit of a nomenclature faux pas. The firmware starts the machine, you talk to the firmware via UEFI.

This post skips all the interesting things in the modern firmware dance. Not the least of which is when you call ExitBootServices() you're already in long mode. There's no need for the journey through real and protected.

Re: The Linux Boot Process: From Power Button to Kernel

#18

Post by nightshift1 »

zahlman wrote: post #8
nightshift1 wrote: post #7

The topic is interesting but it seems to be targeted for my grandmother.

> When power stabilizes, the CPU resets itself to a tiny, old‑fashioned mode called real mode. Real mode dates back to the original 8086 chip. The rules are simple on purpose. Memory addresses are built from two values the CPU keeps in special fast storage called registers. You combine a segment and an offset like this: physical_address = (segment Your grandmother sounds unusually proficient with this sort of thing.

I dont know, i just don't like the tone. This is a complex subject where the target audience should probably already know what is an hexadecimal number or an interrupt and the explanation of a cpu register ought to be better than: "A register is a tiny slot inside the CPU. It holds a number the CPU is using right now." If the subject interest you, you deserve better.

Re: The Linux Boot Process: From Power Button to Kernel

#19

Post by nightshift1 »

kuekacang wrote: post #15
hamasho wrote: post #14

Funny how those three posts are in hacker news top 5 now. I guess today is the low level appreciation day. * The Linux Boot Process: From Power Button to Kernel * The Journey Before main() * How programs get run: ELF binaries (2015) (lwn.net) edit: format

Oh hey, a fellow noticing person!

yes, and the bar is not at all at the same level.
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