Messages in this thread | | | From | (Eric W. Biederman) | Subject | Re: [RFC] ELF Relocatable x86 and x86_64 bzImages | Date | Tue, 08 Aug 2006 01:23:15 -0600 |
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Horms <horms@verge.net.au> writes:
> On Mon, Aug 07, 2006 at 09:32:23PM -0700, H. Peter Anvin wrote: >> Horms wrote: >> > >> >I also agree that it is non-intitive. But I wonder if a cleaner >> >fix would be to remove CONFIG_PHYSICAL_START all together. Isn't >> >it just a work around for the kernel not being relocatable, or >> >are there uses for it that relocation can't replace? >> > >> >> Yes, booting with the 2^n existing bootloaders. > > Ok, I must be confused then. I though CONFIG_PHYSICAL_START was > introduced in order to allow an alternative address to be provided for > kdump, and that previously it was hard-coded to some > architecture-specific value. > > What I was really getting as is if it needs to be configurable at > compile time or not. Obviously there needs to be some sane default > regardless.
CONFIG_PHYSICAL_START has had 2 uses. 1) To allow a kernel to run a completely different address for use with kexec on panic. 2) To allow the kernel to be better aligned for better performance.
For maintenance reasons I propose we introduce CONFIG_PHYSICAL_ALIGN. Which will round our load address up to the nearest aligned address and run the kernel there. That is roughly what I am doing on x86_64 at this point.
s/CONFIG_PHYSICAL_START/CONFIG_PHYSICAL_ALIGN/ gives me well defined behavior and allows the alignment optimization without getting into weird semantics.
Before CONFIG_PHYSICAL_START we _always_ ran the arch/i386 kernel where it was loaded and I assumed we always would. Since people have realized better aligned kernels can run better this assumption became false. Going to CONFIG_PHYSICAL_ALIGN allows us to return to the simple assumption of always running the kernel where it is loaded modulo a little extra alignment.
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