Platform-dependent issues on "stable" (1.7.1) systemtap in Debian Wheezy

Platform-dependent issues on "stable" (1.7.1) systemtap in Debian Wheezy

[Maxim Timchenko]

Hi all,

I'm looking at an issue with the stable version of systemtap (1.7.1)
on Wheezy and hitting an issue only when running on i686 (x86_64 works
fine) - a specific probe (tty_read) is apparently getting its
parameters wrong and gives a kernelspace memory access error. Looking
a bit further in, the tty driver structure within the probe (or when
hooking the corresponding n_tty_read kernel function) doesn't have the
correct magic set, so other members of the structure are probably
garbage too and dereferencing causes the error message. The tty_write
probe is working perfectly and the parameters look correct.

Does the Debian version work with a specific kernel version/arch, or
is it expected to work on any kernel package released by the distro? I
started with the latest and downgraded to what works for me on x86_64
without any improvement (3.2.63-2+deb7u2). I tried deleting the
.systemtap to clear up any temporary files (advice from a random
website).

Is it worth pursuing the resolution on the stable version, or should I
just give up the idea of using packaged versions and build the latest
version of systemtap, and perhaps the latest kernel too, on the same
machine and toolset?

Yours,
-- 
Max

Re: Platform-dependent issues on "stable" (1.7.1) systemtap in Debian Wheezy

[Frank Ch. Eigler]

Hi, Maxim -


maxvt wrote:

> I'm looking at an issue with the stable version of systemtap (1.7.1)
> on Wheezy

(Note that I can't speak for Debian packager folks.)


> and hitting an issue only when running on i686 (x86_64 works fine) -
> a specific probe (tty_read) is apparently getting its parameters
> wrong and gives a kernelspace memory access error.

Is systemtap looking for the parameters in the wrong spot, or are the
values perhaps not yet available (not yet paged in)?  Have you tried
prologue-searching mode (stap -P), or statement probes?


> [...] Does the Debian version work with a specific kernel
> version/arch, or is it expected to work on any kernel package
> released by the distro?

Very roughly speaking, systemtap works with any kernel same age or
older than that systemtap version; access to that kernel's debugging
symbols may be required, depending on the probes in the script.


> [...]  Is it worth pursuing the resolution on the stable version, or
> should I just give up the idea of using packaged versions and build
> the latest version of systemtap, and perhaps the latest kernel too,
> on the same machine and toolset?

I'd probably try a newer systemtap with your preexisting kernel first.


- FChE