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Re: Status of revivesa

On Sat, Sep 27, 2008 at 06:33:46AM +0200, Quentin Garnier wrote:
> On Fri, Sep 26, 2008 at 08:44:29PM -0700, Bill Stouder-Studenmund wrote:
> [...]
> > 
> > I would appreciate debugging assistance. The exact specifics of upcall 
> > delivery are things that I'd hoped to leave as-was & have work. It is the 
> > one area I'm not too strong at.
> I have bad news, at least for 3.x users.  I know very well the
> difference between 3.x and 4.x because I did the commit (and the lengthy
> debugging before that) that produces the behaviour.
> libpthread used to use hard-coded values for the initial context of new
> threads or upcall handlers.  That didn't work under COMPAT_NETBSD32
> because the order of the GDT entries was different, thus the hard-coded
> values were illegal.  So I changed that to use the current values for
> the segment registers.

So the NetBSD 3.X libpthread had a problem w/ COMPAT_NETBSD32, and the 
NetBSD 4.X did not. But non-COMPAT_NETBSD32 usage didn't notice a 

> What happens now is that the order of GDT entries changed in i386.  See
> revision 1.42 of sys/arch/i386/include/segments.h, and that make the
> value of CS used by 3.x's libpthread invalid (selecting GUDATA instead
> of GUCODE).

Then this change, between 4.x and 5.x, changed things such that 
non-COMPAT_NETBSD32 now notices the issue fixed above.

> Andrew will have to confirm, but the comments say that the new order is
> mandatory for sysenter.  That said, AFAIK, we don't use sysenter by
> default.  The only way to use it is to compile libc with -DI686_LIBC, so
> we have the option of providing the compatibility as long as the user
> accepts not to use sysenter.

My "perfect world" solution would be to make the sysenter-compatible 
reshuffling an option and make COMPAT_30_PTHREAD or some such another 
option, and make the two incompatible. That way an admin can clearly 
select which way to go. If either were a default, I'd make the sysenter 
one default. :-)

The upshot, though, is that this means that revivesa didn't break this. So 
does anyone else have any issues that should be examined before a merge? 
The only one I see is to verify that I'm not really seeing a crash of 
named on boot.

Take care,


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