* R.F.C. Should we abandon User-land probes?
@ 2005-10-20 18:16 James Dickens
2005-10-20 18:53 ` Frank Ch. Eigler
2005-10-20 22:31 ` Richard J Moore
0 siblings, 2 replies; 10+ messages in thread
From: James Dickens @ 2005-10-20 18:16 UTC (permalink / raw)
To: SystemTAP
Hi
Because of Systemtap's language lack of support for structs, unions,
typedefs, Systemtap ends up just being a counter, couldn't a userland
app be written to count the number of times a function is called.
The lack of support for those language construct is bad enough for
kernel probes, it can be worked around with pre-made tapsets, but are
we going to write custom tapsets for every app every written?
Guru-mode is no solution, do we have to disable all the work the
Systemtap coders to make Systemtap as safe as possible. Guru-mode can
never be used in a production system without lots of testing. In the
end it would be easier to use other methods, to debug the problem.
Resorting to Guru-mode makes the system unstable. You end up debugging
your script, instead of debugging the app.
Further more, the chance of having an app pass a bad pointer increases
dramatically and may even be the reason they are probing the app in
the first place. As we all know passing a bad pointer in a userland
app, crashes the app, but do the same in the kernel we get an oops, or
the system crashes. You may even write code to handle such events in
Systemtap but that isn't used in guru-mode.
The only way I see that Systemtap can be useful with userland probes
is to implement support for structs, unions and typedefs. It would be
even more helpful if you implement cpp support, so you can include
header files into scripts.
James Dickens
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: R.F.C. Should we abandon User-land probes?
2005-10-20 18:16 R.F.C. Should we abandon User-land probes? James Dickens
@ 2005-10-20 18:53 ` Frank Ch. Eigler
2005-10-20 19:08 ` James Dickens
2005-10-20 22:31 ` Richard J Moore
1 sibling, 1 reply; 10+ messages in thread
From: Frank Ch. Eigler @ 2005-10-20 18:53 UTC (permalink / raw)
To: James Dickens; +Cc: SystemTAP
jamesd.wi wrote:
> [...] The only way I see that Systemtap can be useful with userland
> probes is to implement support for structs, unions and typedefs.
> [...]
Do you mean you want to build complex structures in your script? If
so, what does this have to do with probing that targets kernel vs user
space? Or else are you under the impression that systemtap can't
know/expose such structured data types present in the probed target
software? Perhaps you need to pay more attention to the project
instead of chicken-little editorializing.
- FChE
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: R.F.C. Should we abandon User-land probes?
2005-10-20 18:53 ` Frank Ch. Eigler
@ 2005-10-20 19:08 ` James Dickens
[not found] ` <20051020192356.GD2761@redhat.com>
0 siblings, 1 reply; 10+ messages in thread
From: James Dickens @ 2005-10-20 19:08 UTC (permalink / raw)
To: Frank Ch. Eigler; +Cc: SystemTAP
On 20 Oct 2005 14:53:14 -0400, Frank Ch. Eigler <fche@redhat.com> wrote:
[snip]
>
> Do you mean you want to build complex structures in your script? If
> so, what does this have to do with probing that targets kernel vs user
> space? Or else are you under the impression that systemtap can't
> know/expose such structured data types present in the probed target
> software? Perhaps you need to pay more attention to the project
> instead of chicken-little editorializing.
No I want to access components of complex structures that are pasted
to user land functions. Rarely do complex userland apps just use int,
long, and char *'s. This is especially the case with C++ that pass
class structures. Yes you can make this work in gurumode, but as i
said this disables all the saftety measures systemtap programmers have
worked on.
James
>
> - FChE
>
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: R.F.C. Should we abandon User-land probes?
2005-10-20 18:16 R.F.C. Should we abandon User-land probes? James Dickens
2005-10-20 18:53 ` Frank Ch. Eigler
@ 2005-10-20 22:31 ` Richard J Moore
1 sibling, 0 replies; 10+ messages in thread
From: Richard J Moore @ 2005-10-20 22:31 UTC (permalink / raw)
To: James Dickens; +Cc: SystemTAP
systemtap-owner@sources.redhat.com wrote on 20/10/2005 19:15:59:
> Hi
>
> Because of Systemtap's language lack of support for structs, unions,
> typedefs, Systemtap ends up just being a counter, couldn't a userland
> app be written to count the number of times a function is called.
>
> The lack of support for those language construct is bad enough for
> kernel probes, it can be worked around with pre-made tapsets, but are
> we going to write custom tapsets for every app every written?
>
> Guru-mode is no solution, do we have to disable all the work the
> Systemtap coders to make Systemtap as safe as possible. Guru-mode can
> never be used in a production system without lots of testing. In the
> end it would be easier to use other methods, to debug the problem.
> Resorting to Guru-mode makes the system unstable. You end up debugging
> your script, instead of debugging the app.
>
> Further more, the chance of having an app pass a bad pointer increases
> dramatically and may even be the reason they are probing the app in
> the first place. As we all know passing a bad pointer in a userland
> app, crashes the app, but do the same in the kernel we get an oops, or
> the system crashes. You may even write code to handle such events in
> Systemtap but that isn't used in guru-mode.
>
> The only way I see that Systemtap can be useful with userland probes
> is to implement support for structs, unions and typedefs. It would be
> even more helpful if you implement cpp support, so you can include
> header files into scripts.
>
I disagree entirely.
Whether user-mode probes are useful given the current functionality depends
on the purpose to which they are being put. From the perspective of having
to diagnose some hard-to-reproduce load-realted problem I would find the
current functionality essential. If necessary I would objump -S the user
code in order to determine what to place my probes and what data to
examine. If it helps me debug an obscure but severe problem then I'll take
whatever help I can get.
Don't throw out the baby with the bathwater.
Richard J Moore (LTC, IBM)
> James Dickens
^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2005-10-21 16:01 UTC | newest]
Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2005-10-20 18:16 R.F.C. Should we abandon User-land probes? James Dickens
2005-10-20 18:53 ` Frank Ch. Eigler
2005-10-20 19:08 ` James Dickens
[not found] ` <20051020192356.GD2761@redhat.com>
[not found] ` <cd09bdd10510201302i44a8a6fdy7f4cea33576bec0b@mail.gmail.com>
2005-10-20 20:06 ` Fwd: " James Dickens
2005-10-20 20:14 ` Martin Hunt
2005-10-20 20:18 ` James Dickens
2005-10-20 20:20 ` Fwd: " James Dickens
2005-10-20 20:45 ` Martin Hunt
2005-10-21 16:01 ` Frank Ch. Eigler
2005-10-20 22:31 ` Richard J Moore
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