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Comment by arp242 | Hacker News Reader

> Why not just start the CPU in "long mode", which is what everyone is using it for, in the first place?

Are you sure it's "everyone"? No doubt it's "overwhelming majority", but that's not the same, and "everyone" is a lot of people.

As I understand how this works, the compatibility is perhaps slightly inconvenient to a small group of developers, but not that inconvenient and generally relatively cheap. So why not have and keep it?

ARM has a lot less history than x86. Yes, it goes back to 1985 in the BBC Micro, but didn't really see serious usage as a "generic platform" until the late 90s/early 2000s.

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Do you ever boot your machine only into 32-bit mode? Most UEFI firmware I've seen is launching /EFI/BOOT/BOOTX64.EFI, which means your bootloader is in long mode even if you then switch back to 32-bit mode (and UEFI is likely already there). I don't know if emulating a traditional bios avoids this or not, never thought about it. But I'd take a guess that the vast majority of people are passing through long mode and then back again if they installed a 32-bit OS.

I'm not saying remove the possibility of 32-bit userspace and nor are, it seems, freebsd. I am saying don't bother with a 32-bit kernel. Otherwise you're limited to a 4GB address space and hacks like PAE. No harm in running 32-bit binaries if you want and, I think Solaris actually left userspace as 32-bit only even on their 64-bit OS, unless the application really benefited from a 64-bit setup. Not sure what they do now, been a while since I used it.

It's arguable ASLR only works well in a 64-bit mode, as well.

> Do you ever boot your machine only into 32-bit mode?

No, but I'm not everyone.

Or let me put it this way: I don't know the motivation for why the things work like they do. It's entirely possible there is no good reason at all. Or maybe there is? Either way, I wouldn't assume anything so quickly.

Intel is currently trying to find out if it's everyone. The whole point of announcing the idea of dropping the old modes years before you plan to actually do so is to give a chance for people to speak up if it's a problem.

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