README (1328B)
1 Elfhack is a program to optimize ELF binaries for size and cold startup 2 speed. 3 4 Presently, it is quite experimental, though it works well for the target 5 it was created for: Firefox's libxul.so. 6 7 Elfhack currently only does one thing: packing dynamic relocations ; 8 which ends up being a quite complex task, that can be summarized this 9 way: 10 - Remove RELATIVE relocations from the .rel.dyn/.rela.dyn section. 11 - Inject a small code able to apply relative relocations "by hand" 12 after the .rel.dyn/.rela.dyn section. 13 - Inject a section containing relocative relocations in a different 14 and more packed format, after the small code. 15 - Register the small code as DT_INIT function. Make the small code call 16 what was initially the DT_INIT function, if there was one. 17 - Remove the hole between the new section containing relative 18 relocations and the following sections, adjusting offsets and base 19 addresses accordingly. 20 - Adjust PT_LOAD entries to fit new offsets, and add an additional 21 PT_LOAD entry when that is necessary to handle the discrepancy between 22 offsets and base addresses, meaning the section offsets may yet again 23 need adjustments. 24 - Adjust various DT_* dynamic tags to fit the new ELF layout. 25 - Adjust section headers. 26 - Adjust ELF headers. 27 28 See http://glandium.org/blog/?p=1177#relocations for some figures.