[Bug kprobes/22772] missing kernel/module debuginfo for custom lt kernel

["ocket8888 at gmail dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=22772

--- Comment #13 from ocket8888 <ocket8888 at gmail dot com> ---
(In reply to ocket8888 from comment #10)
> (In reply to David Smith from comment #4)
> > (In reply to ocket8888 from comment #0)
> > > Created attachment 10770 [details]
> > > kernel configuration
> > > 
> > > I've been trying (and failing) to get systemtap to work on my CentOS machine.
> > > ```
> > >     $ uname -a
> > >     Linux ipcdn-cache-51.cdnlab.comcast.net 4.9.70-1.el7.centos.x86_64 #1
> > > SMP Thu Feb 1 15:34:43 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
> > >     $ cat /etc/centos-release```
> > >     CentOS Linux release 7.4.1708 (Core)
> > >     $ stap --version
> > >     Systemtap translator/driver (version 3.1/0.168, rpm 3.1-5.el7_4)
> > > Copyright (C) 2005-2017 Red Hat, Inc. and others
> > > This is free software; see the source for copying conditions.
> > > tested kernel versions: 2.6.18 ... 4.10-rc8
> > > enabled features: AVAHI BOOST_STRING_REF DYNINST JAVA PYTHON2 LIBRPM
> > > LIBSQLITE3 LIBVIRT LIBXML2 NLS NSS READLINE
> > > ```
> > > 
> > > I'm attaching the configuration used to build the kernel, note that it
> > > follows the configuration specified in the FAQ (Q2). When I run the test
> > > command `stap -ve 'probe vfs.read{exit()}` it outputs
> > > 
> > > ```
> > >     Pass 1: parsed user script and 529 library scripts using
> > > 378212virt/192180res/6484shr/188296data kb, in 2030usr/40sys/2078real ms.
> > >     semantic error: while resolving probe point: identifier 'kernel' at
> > > /usr/share/systemtap/tapset/linux/vfs.stp:915:18
> > >         source: probe vfs.read = kernel.function("vfs_read")
> > >                                  ^
> > > 
> > >     semantic error: missing x86_64 kernel/module debuginfo [man
> > > warning::debuginfo] under '/lib/modules/4.9.70-1.el7.centos.x86_64/build'
> > 
> > Interesting. I'm betting the '-lt' tag is going to show up in the filenames
> > installed by one (or more) of the kernel-lt packages. Pay close attention to
> > the following packages: kernel-lt, kernel-lt-debuginfo, and kernel-lt-devel.
> > Does '-lt' show up in any of the filenames from those packages?
> > 
> > If so, an semi-easy workaround here would be to create a symbolic link from
> > the path systemtap expects to the path containing '-lt'.
> > 
> > If I'm right, I'm not sure what the best solution to this problem would be
> > in systemtap to automatically recognize the '-lt' kernels.
> 
> Here's what I got:
> 
> ```
>     $ repoquery -l kernel-lt-`uname -r` | grep -e "-lt"
>     /etc/ld.so.conf.d/kernel-lt-4.9.70-1.el7.centos.x86_64.conf
> ```
> 
> the devel package installs nothing with '-lt' in the name, while the
> debuginfo package dumped too much stuff to paste, but what might be the
> issue is everything it puts under /usr/src is under a 'kernel-lt-4.9.70'
> directory.

Also, I made the links
```
    /usr/lib/debug.dwz/kernel-4.9.70-1.el7.centos.x86_64 ->
/usr/lib/debug.dwz/kernel-lt-4.9.70-1.el7.centos.x86_64
    /usr/src/debug/kernel-4.9.70 -> /usr/src/debug/kernel-lt-4.9.70
    /etc/ld.so.conf.d/kernel-4.9.70-1.el7.centos.x86_64.conf ->
/etc/ld.so.conf.d/kernel-/t-4.9.70-1.el7.centos.x86_64.conf
```
and that hasn't fixed it, but I haven't tried rebooting or reinstalling stap
yet, if you think that'd help. I can't see how it would tbh, which is why I
haven't done it yet, but clearly I have no idea what I'm doing so.... ¯\_(ツ)_/¯

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