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29 lines
1.3 KiB
Plaintext
29 lines
1.3 KiB
Plaintext
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Elfhack is a program to optimize ELF binaries for size and cold startup
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speed.
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Presently, it is quite experimental, though it works well for the target
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it was created for: Firefox's libxul.so.
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Elfhack currently only does one thing: packing dynamic relocations ;
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which ends up being a quite complex task, that can be summarized this
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way:
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- Remove RELATIVE relocations from the .rel.dyn/.rela.dyn section.
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- Inject a small code able to apply relative relocations "by hand"
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after the .rel.dyn/.rela.dyn section.
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- Inject a section containing relocative relocations in a different
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and more packed format, after the small code.
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- Register the small code as DT_INIT function. Make the small code call
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what was initially the DT_INIT function, if there was one.
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- Remove the hole between the new section containing relative
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relocations and the following sections, adjusting offsets and base
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addresses accordingly.
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- Adjust PT_LOAD entries to fit new offsets, and add an additional
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PT_LOAD entry when that is necessary to handle the discrepancy between
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offsets and base addresses, meaning the section offsets may yet again
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need adjustments.
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- Adjust various DT_* dynamic tags to fit the new ELF layout.
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- Adjust section headers.
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- Adjust ELF headers.
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See http://glandium.org/blog/?p=1177#relocations for some figures.
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