[Bug libdw/22452] Extend ebl_reloc_ hooks with relocations against load address for use in libdwfl/relocate.c
mark at klomp dot org
Mon Mar 5 12:52:00 GMT 2018
Mark Wielaard <mark at klomp dot org> changed:
What |Removed |Added
--- Comment #16 from Mark Wielaard <mark at klomp dot org> ---
(In reply to Mark Wielaard from comment #15)
> Did you manage to get a kernel build change upstream?
> It would be nice to point people at it in this bug in case they hit the same
> issue. So they know how to rebuild their kernel.
Author: Hendrik Brueckner <firstname.lastname@example.org>
Date: Mon Nov 20 11:41:07 2017 +0100
s390/kernel: emit CFI data in .debug_frame and discard .eh_frame sections
Using perf probe and libdw on kernel modules failed to find CFI
data for symbols. The CFI data is stored in the .eh_frame section.
The elfutils libdw is not able to extract the CFI data correctly,
because the .eh_frame section requires "non-simple" relocations
for kernel modules.
The suggestion is to avoid these "non-simple" relocations by emitting
the CFI data in the .debug_frame section. Let gcc emit respective
directives by specifying the -fno-asynchronous-unwind-tables option.
Using the .debug_frame section for CFI data, the .eh_frame section
becomes unused and, thus, discard it for kernel and modules builds
The vDSO requires the .eh_frame section and, hence, emit the CFI data
in both, the .eh_frame and .debug_frame sections.
See also discussion on elfutils/libdw bugzilla:
Suggested-by: Mark Wielaard <email@example.com>
Signed-off-by: Hendrik Brueckner <firstname.lastname@example.org>
Reviewed-by: Heiko Carstens <email@example.com>
Signed-off-by: Martin Schwidefsky <firstname.lastname@example.org>
> I have retitled this bug and will keep it open in case someone has
> time for implementing the ebl hooks for relative load address relocations.
I think the above kernel fix is a better. And there really is not much benefit
to have relative load address relocations for .eh_frame except for these ET_REL
.ko files. Also, nobody seems to have time. So lets close this for now.
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