Comment 2 for bug 1741992

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bugproxy (bugproxy) wrote : [1/3] powerpc/modules: Add REL24 relocation support of livepatch symbols

------- Comment on attachment From <email address hidden> 2018-01-09 01:39 EDT-------

Livepatch re-uses module loader function apply_relocate_add() to write
relocations, instead of managing them by arch-dependent
klp_write_module_reloc() function.

apply_relocate_add() doesn't understand livepatch symbols (marked with
SHN_LIVEPATCH symbol section index) and assumes them to be local
symbols by default for R_PPC64_REL24 relocation type. It fails with an
error, when trying to calculate offset with local_entry_offset():

  module_64: kpatch_meminfo: REL24 -1152921504897399800 out of range!

Whereas livepatch symbols are essentially SHN_UNDEF, should be called
via stub used for global calls. This issue can be fixed by teaching
apply_relocate_add() to handle both SHN_UNDEF/SHN_LIVEPATCH symbols
via the same stub. This patch extends SHN_UNDEF code to handle
livepatch symbols too.