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

brueckner at linux dot vnet.ibm.com sourceware-bugzilla@sourceware.org
Fri Nov 17 15:38:00 GMT 2017


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

--- Comment #2 from H. Brueckner <brueckner at linux dot vnet.ibm.com> ---
(In reply to Mark Wielaard from comment #1)
> I haven't investigated fully yet.
> But I did take a quick look at the paes_s390.ko.debug file.
> A few quick comments as early feedback.
> 
> Note that it doesn't contain .debug_frame but only a .eh_frame section.
> Other architectures force .debug_frame for kernel modules to store the CFI.
> 
> 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.

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.

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