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apk_symbols.md

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APK Symbols

All files in an APK that are not broken down into sub-entries are tracked by a symbol within the .other section. This includes:

  • resources.arsc
  • assets/*
  • res/*

Algorithm

During builds:

  • An $output_dir/size-info/Foo.res.info file is created that records the originating path for each android resource file.

During supersize archive:

For each zip entry:

  • One symbol is created using the compressed size of the entry.
  • Files within res/ are given a source path using the mapping from $output_dir/Foo.apk.res.info
  • Other entries are given a source path of $APK/$zip_path.

Each zip entry incurs additional size overhead from:

  • Zip file local header,
    • Size dependent on filename length and zipalign overhead.
  • Zip file central directory entry,
  • An entry within V1 signature files (META-INF/ files).
    • Applicable only for older minSdkVersion apks, and for system image apks.
  • res/ files have an associated entry within resources.arsc.

Rather than include this overhead in each symbol, they are put altogether into a single Overhead: APK file symbol. Because:

  1. The symbol size is more understandable if it matches the unzip -lv output.
  2. It prevents zipalign overhead from causing many small size changes in diffs.
  3. When looking at size optimizations, it makes more sense to look at the total overhead rather than the per-symbol overhead.