| zipalign -- zip archive alignment tool |
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| usage: zipalign [-f] [-v] <align> infile.zip outfile.zip |
| zipalign -c [-v] <align> infile.zip |
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| -c : check alignment only (does not modify file) |
| -f : overwrite existing outfile.zip |
| -p : page align stored shared object files |
| -v : verbose output |
| <align> is in bytes, e.g. "4" provides 32-bit alignment |
| infile.zip is an existing Zip archive |
| outfile.zip will be created |
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| The purpose of zipalign is to ensure that all uncompressed data starts |
| with a particular alignment relative to the start of the file. This |
| allows those portions to be accessed directly with mmap() even if they |
| contain binary data with alignment restrictions. |
| |
| Some data needs to be word-aligned for easy access, others might benefit |
| from being page-aligned. The adjustment is made by altering the size of |
| the "extra" field in the zip Local File Header sections. Existing data |
| in the "extra" fields may be altered by this process. |
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| Compressed data isn't very useful until it's uncompressed, so there's no |
| need to adjust its alignment. |
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| Alterations to the archive, such as renaming or deleting entries, will |
| potentially disrupt the alignment of the modified entry and all later |
| entries. Files added to an "aligned" archive will not be aligned. |
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| By default, zipalign will not overwrite an existing output file. With the |
| "-f" flag, an existing file will be overwritten. |
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| You can use the "-c" flag to test whether a zip archive is properly aligned. |
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| The "-p" flag aligns any file with a ".so" extension, and which is stored |
| uncompressed in the zip archive, to a 4096-byte page boundary. This |
| facilitates directly loading shared libraries from inside a zip archive. |
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