Re: [Xen-devel] [PATCH 13/20] create-diff-object: Strip all undefined entires of known size

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 8/21/19 9:20 AM, Pawel Wieczorkiewicz wrote:
> The patched ELF object file contains all sections and symbols as
> resulted from the compilation. However, certain symbols may not be
> copied over to the resulting object file, due to being unchanged or
> not included for other reasons.
> In such situation the resulting object file has the entire sections
> copied along (with all their entries unchanged), while some of the
> corresponding symbols are not copied along at all.
> This leads to having incorrect undefined (STN_UNDEF) entries in the
> final hotpatch ELF file.
>
> The newly added function livepatch_strip_undefined_elements() detects
> and removes all undefined RELA entries as well as their corresponding
> PROGBITS section entries.
> Since the sections may contain elements of unknown size (sh.sh_entsize
> == 0), perform the strip only on sections with well defined entry
> sizes.
>
> After replacing the stripped rela list, it is assumed that the next
> invocation of the kpatch_rebuild_rela_section_data() will adjust all
> section header parameters according to the current state.
>
> The livepatch_strip_undefined_elements() is a superset of the
> kpatch_regenerate_special_section() in both scope (covers all RELA
> sections instead of just special sections) and granularity (checks
> all entries instead of whole groups) modulo the entries validity
> predicate.
> Unifying the functions results in a complicated code, which is hard
> to reason about. Thus, the kpatch_regenerate_special_section() is
> kept separate with its own predicate for special sections only, and
> livepatch_strip_undefined_elements() follows for all sections with
> the undefined symbol detecting predicate.
>
> Signed-off-by: Pawel Wieczorkiewicz <wipawel@xxxxxxxxx>
> Reviewed-by: Martin Pohlack <mpohlack@xxxxxxxxx>
> Reviewed-by: Bjoern Doebel <doebel@xxxxxxxxx>
> Reviewed-by: Norbert Manthey <nmanthey@xxxxxxxxx>
> Reviewed-by: Andra-Irina Paraschiv <andraprs@xxxxxxxxxx>
> ---
Reviewed-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

Thanks

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