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Re: backwards compability of systemtap

John Liang wrote:
HI there,

It looks array syntax like "foobar["string",1]" is not supported in stap version 0.5.4 which comes with redhat 4 update 3. But it is definitely supported in stap Version 0.5.8 of redhat 4 update 4.

I am wondering if there is a way to run the compiled the module/C code
of version 0.5.8 on redhat 4 update 3. If yes, then it means I can use the most recent features of systemtap to old version of redhat

When I try this, I got the following message from /var/log/messages:

Mar 12 09:51:19 perf8 kernel: stap_7948: disagrees about version of symbol
Mar 12 09:51:19 perf8 kernel: stap_7948: Unknown symbol register_kprobe

You've got 2 problems here:

1) Kernel version differences (which is probably what you see above). If you take a kernel module compiled against the U4 kernel and try to run it against the U3 kernel, you are going to have problems. It would be possible to install the U3 kernel on your U4 system (but not actually run the U3 kernel), compile the systemtap module against the U3 kernel, then copy it to your U3 system.

But, then you'll come up against:

2) Possible backend differences. I don't deal much with the backend, but there are almost certainly differences between the 0.5.4 and 0.5.8 versions of staprun. The question is can the 0.5.4 staprun handle an 0.5.8 module? I don't believe we've ever tested this (or have ever made any promises that it would/could/should work). Martin Hunt would know more here.

You safest bet would be to compile the 0.5.8 version of systemtap on your U3 system.

David Smith
Red Hat
256.217.0141 (direct)
256.837.0057 (fax)

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