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Elfhack acts as a linker, and it uses the `elf_header` symbol to point at the ELF header in the injected code that applies relocations. Both GNU ld and lld expose a `__ehdr_start` symbol with the same meaning, so rename the `elf_header` symbol for compatibility. This will allow to reuse the code in the upcoming replacement for elfhack. Differential Revision: https://phabricator.services.mozilla.com/D187088 |
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| .. | ||
| inject | ||
| dummy.c | ||
| elf.cpp | ||
| elfhack.cpp | ||
| elfxx.h | ||
| inject.c | ||
| Makefile.in | ||
| moz.build | ||
| README | ||
| test-array.c | ||
| test-ctors.c | ||
| test.c | ||
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.