| 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. |
