Den 05/10/2010 kl. 15.59 skrev Erik Trulsson: > On Tue, Oct 05, 2010 at 03:28:36PM +0200, Erik Cederstrand wrote: >> Hello hackers, >> >> I got reminded of a problem I had a couple of years back compressing >> FreeBSD jails. I was using bsdiff for the compression and found out >> that md5 sums of static libraries (.a files) in /usr/lib and >> /usr/local/lib didn't match between jails, even though the source >> code used to create the jails hadn't changed. One of my goals is to >> detect which files in a distribution change between two commits. >> >> It turns out that timestamps are stored in the library: > > Yes, they are. That is because the file format used for static > libraries include a timestamp for each object file stored in the > archive. > > You can use 'ar -tv /PATH/TO/LIBRARY/libfoo.a' to get a list of the > objects stored in the archive and the corresponding timestamps. > > See the ar(5) manpage for a description of the file format, and the > ar(1) manpage for information on how to manage such files.
Thanks, that was very helpful. It seems I can at least normalize the .a files using something like the following to weed out timestamps and uid/gid: % ar -x /usr/lib/libfetch.a % chown 0:0 * % touch -t 197001010000 * % ar -r libfetch.a `ar -t /usr/lib/libfetch.a` The above takes ca. 10 seconds for all static libraries on my aging machine, which is OK in my case. Unfortunately it seems there's still a creation time of the archive itself that I cant alter using the above, so the md5 sums still don't match: % diff mod.strings orig.strings 2c2 < / 1286312209 0 0 0 958 ` --- > / 1269146263 0 0 0 958 ` Using Python to replace 1286312209 with 1269146263 in the binary file now gives me matching md5 sums. It seems a bit complicated just to get rid of some timestamps, though. Thanks, Erik
