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Re: OpenBSD pch, take 2
- From: Marc Espie <espie at nerim dot net>
- To: Paolo Bonzini <paolo dot bonzini at lu dot unisi dot ch>
- Cc: GCC Development <gcc at gcc dot gnu dot org>
- Date: Mon, 31 Jan 2005 16:10:42 +0100
- Subject: Re: OpenBSD pch, take 2
- References: <20050131121547.GA24600@tetto.home> <41FE451C.email@example.com>
- Reply-to: espie at nerim dot net
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.
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.