Re: [Xen-devel] [livepatch-build-tools part3 v2 3/3] create-diff-object: Strip all undefined entires of known size

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 8/8/19 1:51 PM, 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 code in this patch seems to be very similar (i.e. somewhat 
copy-and-pasted) to kpatch_regenerate_special_section() which prunes the 
rela list and rebuilds the corresponding text section according to the 
predicate should_keep_rela_group(). The intent of the function also 
seems to be the same (only keep elements that are needed).
In what situations does the existing function not do the right thing?

Can should_keep_rela_group() be updated instead?

Thanks,
--
Ross Lagerwall

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