Re: amd64 kernel, i386 userland

[Alan Barrett <apb%cequrux.com@localhost>]

On Tue, 21 Jan 2014, Emmanuel Dreyfus wrote:
> In order to have more RAM without reinstalling everything, 
> using an amd64 kernel on to of a i386 userland seems 
> appealing. netbsd32 emulation works fine, and the machine boots 
> to multiuser without a hassle.
>
> But there are minor problems, with binaries that use ioctl to 
> talk with a kernel subsystem: I spoted ipf and raidctl.

If there are particular ioctls that don't have proper netbsd32 
compat equivalents, they can be fixed on a case by case basis. 
We'd need to start with a list of the problematic ioctls, either 
by noticing what fails, or by systematically searching for ioctls 
whose data includes fields that change size between 32-bit and 
64-bit systems.

I think that we should also avoid adding such problematic kernel 
interfaces in future, by using fixed width types wherever 
possible.

> Things would be much easier if the kernel searched 
> /emul/netbsd64 before / for native binaries. Of course such 
> a behavior cannot be made default because of the performance 
> penalty. But a compile time option would be nice without causing 
> any performance harm to people that do not want it.

I have also sometimes wished for that.

--apb (Alan Barrett)