OpenBSD pch, take 2

[Marc Espie]

On Mon, Jan 31, 2005 at 03:47:56PM +0100, Paolo Bonzini wrote:
> >The very nasty thing is that they will *appear* to work. Namely, loading
> >a pch file will work 95% of the time... and fail whenever the file cannot
> >be mmaped at the same address due to randomization issues.
> >So, mark them as completely unreliable.
> 
> You may want to find the largest VMA and make the PCH reside in the 200 
> MB in the middle of it, or allocate the topmost free 200 MB in the 
> address space, etc.
> 
> Linux has similar problems, see host-linux.c.  If you bring the 
> percentage up to 99% or so, it can be ok because PCH should only cause a 
> compilation slowdown rather than incorrect results.
> 
> Paolo

Nope.
It doesn't work. Specifying pch on the command line will fail if the pch
loading doesn't work, it won't revert gracefully to normal headers.

And it's not a question of finding an address that works, no address works.

And 99% is not acceptable. How would you feel if you had this nifty
compilation procedure that works only 99% of the time and fails the
remaining 1% ?  This means that every automated build is doomed. Thus
pch are totally unfit for production on OpenBSD.