owl-dev - Re: [bugzilla-daemon@...nvz.org: [Bug 1801] VDSO: Not enough room for program headers]

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Message-ID: <20110306115535.GA688@openwall.com>
Date: Sun, 6 Mar 2011 14:55:35 +0300
From: Solar Designer <solar@...nwall.com>
To: owl-dev@...ts.openwall.com
Subject: Re: [bugzilla-daemon@...nvz.org: [Bug 1801] VDSO: Not enough room for program headers]

On Sat, Mar 05, 2011 at 11:12:47PM +0300, Vasiliy Kulikov wrote:
> Reply from OpenVZ about the kernel build failure.

Thanks!  Well, we have a problem, which is not exactly surprising. ;-)
We knew we were using an unsupported version combination; we just did
not have time to update gcc before Owl 3.0, and doing it shortly before
the release could break other things (at least, we would not know if the
system is stable or not until more time would pass).

I've just posted a lengthy followup:

http://bugzilla.openvz.org/show_bug.cgi?id=1801#c2

Maybe Pavel or someone else will post something helpful in response, but
so far it looks like we're to patch the vdso issue on our own.  I suggest
that you look into it in a few days from now, unless another solution
emerges (e.g., Pavel changes his mind and takes care of the issue for
us, but this is unlikely because he won't even be able to get to that
point in the compile without our existing patches... we'd need to
provide full reproduction instructions first).

> --- Comment #1 from Pavel Emelyanov <xemul@...nvz.org> 2011-03-05 15:04:42 EST ---
> I'm not going to fix it. I've seen enough cases when rhel5 kernel (and others
> too) didn't even work when was compiled with too old/new gcc.
> 
> I use 4.1.2 20080704 for official builds, use some adjacent ones.
> 
> -- 
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> ----- End forwarded message -----

Alexander

P.S. My reply to Pavel, pasted in here just in case:

---
Solar Designer      2011-03-06 06:42:41 EST

Pavel - thank you for your prompt reply.  I understand and respect your
decision and the rationale behind it, yet I'd like to communicate more info to
you:

This is not an end-user's question/report/request.  We're using these kernels
in our distro, Owl.  One of the design principles of Owl is to include just one
version of a component in the distro, especially for a major/large component
such as gcc.  Thus, we can't reasonably have the kernel alone dictate the
version of gcc for us to use.  Rather, we need to pick a version of gcc that
works for everything we include in the distro at once, and moreover whenever we
update gcc we obviously want to update to the latest.  Sometimes this requires
patches.

At this time, we have gcc 3.4.5 in Owl 3.0-stable and in Owl-current.  The plan
is for Owl-current to move to latest stable gcc soon, which means to 4.5.x or
4.6.x.  We also intend to move from your rhel5 to your rhel6 kernels, though,
so we might make both changes at the same time if we have to (although it'd be
more convenient for us to make them as separate steps).

We also need to maintain Owl 3.0-stable with its gcc 3.4.5.  We need to issue
kernel updates for this Owl branch at least for the security fixes.  This means
that we need further rhel5 branch kernels compilable by gcc 3.4.5.

So far, our experience with your rhel5 branch kernels with our gcc 3.4.5 has
been mostly positive.  We're in fact patching a few things for the compile to
succeed (it's just that this vdso thing is new, not patched by us yet, and it
might be trickier to patch), but then those kernels work in production reliably
enough (as in: hundreds of days of uptime under serious load for older rhel5
branch kernels, such as -128 and -164, compiled with gcc 3.4.5; no problems
with -194 either, it's just not that old yet for "hundreds of days").

So it looks like we'll need to patch this vdso thing on our own in order to be
able to move beyond -238.1.1.el5.028stab084.3, which we currently have in
Owl-current.  While we could and intend to update to gcc 4.5+ in Owl-current,
we'll need those kernels working with gcc 3.4.5 for Owl 3.0-stable anyway.

Any comments, suggestions?

Also, while we're at it, what versions of gcc do you support for your rhel6
branch kernels?

Thanks again,

Alexander
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