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[armel/marvell] Disable features to shrink kernel image (fixes FTBFS)

Salvatore Bonaccorso requested to merge carnil/linux:bookworm-shrink-armel-image into bookworm

This is following the idea which Ben Hutchings applied earlier in 9dfe6d33 ("[armel/marvell: Disable features to shrink kernel image (fixes FTBFS)").

In the latest armel build for bookworm-security (6.1.52-1), the compressed image for marvell increased and was about 24K too large:

Image size 2753652/2729712, using 100.88%. Too large. Refusing to continue.

In the upstream changes Ben did found there were two commits in 6.2 which each increased the image size substantially:

  • 60443c88f3a8 "kallsyms: Improve the performance of kallsyms_lookup_name()". Disabling KALLSYMS (and FUNCTION_TRACER which selects it) would save ~360K (!), but it looks like many user- space programs need /proc/kallsyms. We already disable KALLSYMS_ALL to reduce the number of symbols included.
  • f4d6b94b40c9 "apparmor: use zstd compression for profile data" made SECURITY_APPARMOR_EXPORT_BINARY select ZSTD_COMPRESS, which would otherwise be modular. This option is mostly useful for checkpoint/ restore which we already disable, so seems safe to disable.

For first of those was later on backported to 6.1.42. Following the same reasoning, it might be possible to disable two of the features without much impact:

  • MPTCP costs ~40K and is mostly useful for mobile devices or servers supporting them.
  • FUNCTION_TRACER costs ~90K and is mostly useful for debugging.

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