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| -rw-r--r-- | build/unix/elfhack/README | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/build/unix/elfhack/README b/build/unix/elfhack/README new file mode 100644 index 0000000000..8c68031e33 --- /dev/null +++ b/build/unix/elfhack/README @@ -0,0 +1,28 @@ +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. |