Re: Anyone tried SystemTap with the latest RHEL5 Beta refresh

[David Wilder <dwilder at us dot ibm dot com>]

David Smith wrote:

> David Wilder wrote:
>
> > Frank Ch. Eigler wrote:
> >
> > > "Ken Robson" <ken@odtv.com> writes:
> > >
> > >  
> > >
> > > > [...]  To me it is valid to install minus the debuginfo files on
> > > > almost all Production hosts.  I am experimenting with developing my
> > > > scripts off box with my cache directory set to an exported read-only
> > > > NFS share which is then mounted as the module cache directory on my
> > > > Production boxes [...]
> > > >   
> > >
> > >
> > > More than that - on such production boxes, you will need to install
> > > only the "staprun" (formerly "stapd") binary, now separated into a
> > > systemtap-runtime RPM.  For the moment though please be careful with
> > > building probes for mismatching machines: the module address tables
> > > are not yet fully adaptive.
> > >
> > > - FChE
> > >  
> > The cached debuginfo is a really cool concept.
>
>
> You got a bit confused here.  The debuginfo isn't cached, the 
> systemtap compiled modules are cached.


Thanks for the clarification.

> > But it wont solve the problem of simplifying the use of systemtap for 
> > the customers. From a support standpoint if a customer system is 
> > missing a debug tool (or some dependent component) the tool may as 
> > well not exist! If it comes down to fix the debug tool or find 
> > another approach to solve the customers problem the later will 
> > generally win. To make stap successful we need to get people using it 
> > and providing feedback, let's make it as easy as possible to use. All 
> > dependencies must be installed when selecting a product for install.
>
>
> In general, I certainly agree with you that all dependencies must be 
> installed.
>
> However, systemtap (and any other program that would like to use 
> debuginfo) is a special case.  From my understanding, there is a 
> policy (perhaps unwritten) that no rpm can require a debuginfo rpm.  
> Plus, even if we did require the debuginfo rpm, it still wouldn't get 
> installed automatically.  For FC[56], the debuginfo yum repositories 
> are disabled by default.  For RHEL[34], the debuginfo RPMs aren't 
> available from a RHN channel, they have to be downloaded separately 
> (from my vague understanding which could be wrong).  In addition, 
> debuginfo RPMs are not present on RHEL/FC install media.  So, from a 
> current logistical point of view, if the systemtap RPM required the 
> kernel debuginfo RPM, systemtap itself could never be installed 
> because of missing dependencies that could never be met.
>
> Currently, using systemtap isn't much different than using gdb.  Let's 
> assume that /bin/ls keeps crashing on you for some strange reason that 
> you'd like to debug.  You are going to need to download/install the 
> coreutils debuginfo RPM, then use gdb to debug your problem.
Yea but gdb has other uses then debugging coreutils.  SystemTap is only 
used to instrument the kernel.

The more I think about it,  installing the debug info package at install 
time(ignoring the packaging issue for now) solves only half the 
problem.  The other half is,  when the kernel is updated and the 
debuginfo package is not, then stap breaks.

I bet I'll get a lot of objections to this suggestion....   But here 
goes..   Why not package the debuginfo "vmlinux" with the kernel rpm?  
Just the vmlinux, keep all the debug modules in the debuginfo package.   
I  bet that most of the users of  stap are debugging the kernel proper, 
and vmlinux is all that is needed.  Sure this will increase the size of 
the kernel package by about 40Meg, but the full debug info package is 
closer to 150Meg.

This would also solve the same issue for kdump/crash..

--
David Wilder
IBM Linux Technology Center
Beaverton, Oregon, USA 
dwilder@us.ibm.com
(503)578-3789