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- 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.
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