1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/build/unix/elfhack/README Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,28 @@
1.4 +Elfhack is a program to optimize ELF binaries for size and cold startup
1.5 +speed.
1.6 +
1.7 +Presently, it is quite experimental, though it works well for the target
1.8 +it was created for: Firefox's libxul.so.
1.9 +
1.10 +Elfhack currently only does one thing: packing dynamic relocations ;
1.11 +which ends up being a quite complex task, that can be summarized this
1.12 +way:
1.13 +- Remove RELATIVE relocations from the .rel.dyn/.rela.dyn section.
1.14 +- Inject a small code able to apply relative relocations "by hand"
1.15 + after the .rel.dyn/.rela.dyn section.
1.16 +- Inject a section containing relocative relocations in a different
1.17 + and more packed format, after the small code.
1.18 +- Register the small code as DT_INIT function. Make the small code call
1.19 + what was initially the DT_INIT function, if there was one.
1.20 +- Remove the hole between the new section containing relative
1.21 + relocations and the following sections, adjusting offsets and base
1.22 + addresses accordingly.
1.23 +- Adjust PT_LOAD entries to fit new offsets, and add an additional
1.24 + PT_LOAD entry when that is necessary to handle the discrepancy between
1.25 + offsets and base addresses, meaning the section offsets may yet again
1.26 + need adjustments.
1.27 +- Adjust various DT_* dynamic tags to fit the new ELF layout.
1.28 +- Adjust section headers.
1.29 +- Adjust ELF headers.
1.30 +
1.31 +See http://glandium.org/blog/?p=1177#relocations for some figures.
