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comparison: build/unix/elfhack/README
build/unix/elfhack/README
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- TOR_BUG_3246
- changeset 7
- 129ffea94266
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| 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. |
