1zipalign -- zip archive alignment tool 2 3usage: zipalign [-f] [-v] <align> infile.zip outfile.zip 4 zipalign -c [-v] <align> infile.zip 5 6 -c : check alignment only (does not modify file) 7 -f : overwrite existing outfile.zip 8 -p : page align stored shared object files 9 -v : verbose output 10 <align> is in bytes, e.g. "4" provides 32-bit alignment 11 infile.zip is an existing Zip archive 12 outfile.zip will be created 13 14 15The purpose of zipalign is to ensure that all uncompressed data starts 16with a particular alignment relative to the start of the file. This 17allows those portions to be accessed directly with mmap() even if they 18contain binary data with alignment restrictions. 19 20Some data needs to be word-aligned for easy access, others might benefit 21from being page-aligned. The adjustment is made by altering the size of 22the "extra" field in the zip Local File Header sections. Existing data 23in the "extra" fields may be altered by this process. 24 25Compressed data isn't very useful until it's uncompressed, so there's no 26need to adjust its alignment. 27 28Alterations to the archive, such as renaming or deleting entries, will 29potentially disrupt the alignment of the modified entry and all later 30entries. Files added to an "aligned" archive will not be aligned. 31 32By default, zipalign will not overwrite an existing output file. With the 33"-f" flag, an existing file will be overwritten. 34 35You can use the "-c" flag to test whether a zip archive is properly aligned. 36 37The "-p" flag aligns any file with a ".so" extension, and which is stored 38uncompressed in the zip archive, to a 4096-byte page boundary. This 39facilitates directly loading shared libraries from inside a zip archive. 40 41