[Bug libdw/22452] Failed to obtain CFI data for a OP_call_frame_CFA when looking for func entrypoc in an s390 kernel module

["mark at klomp dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=22452

--- Comment #4 from Mark Wielaard <mark at klomp dot org> ---
(In reply to H. Brueckner from comment #2)
> (In reply to Mark Wielaard from comment #1)
> > The .eh_frame is a loaded section, which means it won't go into the .debug
> > file. So you would need to load the CFI from the main ELF .ko.
> 
> Initially, I have tried on my own kernel build (including debug_info) and
> ran the test program against the .ko file.  (Because I am not permitted to
> share binary code and, please, do not ask why, it is difficult to provide
> you an alternative.  If you have access to a s390 or use a cross-compiler it
> would be fine but that typically requires some effort on your side.

Don't worry, we have the split .ko/.debug files, it should in theory also work
(or show the same bug) with that.

> In any case, if you require some output in text form, please let me know.
> 
> > One tricky issue here is the fact that kernel modules are ET_REL files
> > that still need relocations applied (you can see there is also a
> > .rela.eh_frame section). libdwfl can do simple relocations, but might not
> > know about all relocation types used in an .eh_frame section (I haven't
> > checked yet).
> 
> Ok.

So, if you could provide the output of eu-readelf --relocs paes_s390.ko (on
your combined paes_s390.ko containing both code and debug) that would be
helpful.

If there are relocations in the .rela.eh_frame section that aren't "simple" as
defined in s390_reloc_simple_type (backends/backends/s390_symbol.c) that might
be a hint.

Also if you could trick you kernel build to generate CFI in .debug_frame
instead of .eh_frame like other arches seem to do, that would make a good
testcase.

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