The Tor Browser / file revision

 Elfhack is a program to optimize ELF binaries for size and cold startup

 speed.

 Presently, it is quite experimental, though it works well for the target

 it was created for: Firefox's libxul.so.

 Elfhack currently only does one thing: packing dynamic relocations ;

 which ends up being a quite complex task, that can be summarized this

 way:

 - Remove RELATIVE relocations from the .rel.dyn/.rela.dyn section.

 - Inject a small code able to apply relative relocations "by hand"

   after the .rel.dyn/.rela.dyn section.

 - Inject a section containing relocative relocations in a different

   and more packed format, after the small code.

 - Register the small code as DT_INIT function. Make the small code call

   what was initially the DT_INIT function, if there was one.

 - Remove the hole between the new section containing relative

   relocations and the following sections, adjusting offsets and base

   addresses accordingly.

 - Adjust PT_LOAD entries to fit new offsets, and add an additional

   PT_LOAD entry when that is necessary to handle the discrepancy between

   offsets and base addresses, meaning the section offsets may yet again

   need adjustments.

 - Adjust various DT_* dynamic tags to fit the new ELF layout.

 - Adjust section headers.

 - Adjust ELF headers.

 See http://glandium.org/blog/?p=1177#relocations for some figures.