Re: guru mode: invalid module format

["Serhei Makarov" <me at serhei dot io>]

On Fri, Jun 14, 2019, at 10:55 AM, Serhei Makarov wrote:
> On Thu, Jun 13, 2019, at 7:48 PM, Frank Ch. Eigler wrote:
> > Thanks for your patience.  I have not been able to reproduce this here
> > on Fedora, so didn't look deeper until today.  I believe the problem
> > may be buildrun.cxx:124, which for guru mode adds a
> > CONFIG_MODEVERSIONS= override into the module kbuild makefile.
> > Non-fedora kernels may interpret this differently.
> I haven't been able to reproduce on Ubuntu either. Trying to think if 
> there's any other distribution/kernel where this option is likely to 
> work differently.
> 
> The reproduction steps point to another potential problem -- the 
> regular and guru mode scripts are being compiled differently, but they 
> appear to be treated equivalently by stap's compilation cache. 
> Therefore deleting the cache changes the outcome of $ stap 
> helloworld.stp -g

I pushed a commit to include guru-mode status in the hashing data to avoid this problem.

For overriding SystemTap's current behaviour wrt modversions it may be worth trying
$ stap -B CONFIG_MODVERSIONS=y -g hello.stp

Later I'll test on a kernel config where CONFIG_MODVERSIONS= disabled modules are rejected.
If the problem is too complex, I can revert the change to PR10280, at the cost of more risk when transferring guru-mode modules to a different kernel version.

All the best,
      Serhei