Re: [uml-devel] arch/um/include/kern_util.h:35: error: 'CONFIG_NR_CPUS' undeclared

[Blaisorblade <blaisorblade@yahoo.it>]

On Thursday 19 January 2006 01:08, Jeff Dike wrote:
> On Wed, Jan 18, 2006 at 05:42:56PM +0100, Blaisorblade wrote:
> > What about this? Inserting an asm volatile clobbering all unsaved
> > registers (what I thought for long time)?

> The gcc doc is somewhat confusing.  I read your description as saying
> that locals may be totally smashed to random numbers (and the first
> sentence in the gcc description implies that as well).

I agree with that.

> However, the 
> example they give is a pathological case where a local may have one of
> two (well-defined) values, and it's not defined which of those two
> well-defined values it will end up with.

It's confusing. Standard conformance page says that:

       * On some rare x86 targets, `setjmp' doesn't save the registers
          in all circumstances.  In those cases, GCC doesn't allocate
          any variables in registers unless they are marked `register'.
But we know it's totally wrong.

The example under "Incompatibilities of GCC" is what you say. However, it's 
just because it's a little example. If the var is placed in a register, and 
after a lot you longjmp there, that register is totally smashed.

> > Or taking the libc implementation and suiting
> > it for our use, solving the above problem?

> Yuck.  But how big is it?

Don't know... I suggested this mainly for the volatile vars problem, more than 
for the "access stack" problem.

> Another possibility is to do the magic wakeup thing we do with
> mconsole stack, and have it tell us what it registers are.  Not sure
> if that's any better.

You mean mconsole_kern.c:do_stack()? Hmm, ugly too, but more reliable, and not 
relying on glibc at least.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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