Re: [uml-devel] SKAS mode not working, x86_64 SMP host, x86_64 guest , problems with noprocmm

[Jeff Dike <jdike@addtoit.com>]

On Wed, Oct 18, 2006 at 01:39:55AM +0200, Blaisorblade wrote:
> Jeff, I remember vaguely a recent (>=2.6.17) patch about udelay fixing a 
> misbehaviour, would you please complete my recollection and verify the 
> interaction with this?

There were two problems.

One was that the declaration and definition of most arch
__const_udelay were mismatched.  It was simply a name mismatch, would
not cause miscompilation, but did cause conceptual problems:

arch/i386/lib/delay.c:
	inline void __const_udelay(unsigned long xloops)

include/asm-i386/delay.h:
	extern void __const_udelay(unsigned long usecs);

I'm also somewhat interested in how something that's defined inline in
a C file will be accessible to other files such that an extern
declaration would be needed.

The second problem (IIRC) was the mismatch you noted, although I
can't find that part of the patch any more.  I didn't understand the
magic constants in asm-i386/delay.h, and didn't see the comments in
arch/i386/lib/delay.c, which might have helped.

> This bug is here at least since 2.6.16.
> Suggested solution:
> 1) have _our own_ delay.h, to avoid depending on subarchs' changes
> 2) first avoid playing so complex tricks, then maybe copy their 
> implementation (note it is slightly different already among x86 and
> x86_64).

This sounds reasonable.

				Jeff

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