build/unix/elfhack/README@ac0c01689b40 (annotated)
build/unix/elfhack/README
Thu, 15 Jan 2015 15:59:08 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Thu, 15 Jan 2015 15:59:08 +0100
- branch
- TOR_BUG_9701
- changeset 10
- ac0c01689b40
- permissions
- -rw-r--r--
Implement a real Private Browsing Mode condition by changing the API/ABI;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.
| michael@0 | 1 | Elfhack is a program to optimize ELF binaries for size and cold startup |
| michael@0 | 2 | speed. |
| michael@0 | 3 | |
| michael@0 | 4 | Presently, it is quite experimental, though it works well for the target |
| michael@0 | 5 | it was created for: Firefox's libxul.so. |
| michael@0 | 6 | |
| michael@0 | 7 | Elfhack currently only does one thing: packing dynamic relocations ; |
| michael@0 | 8 | which ends up being a quite complex task, that can be summarized this |
| michael@0 | 9 | way: |
| michael@0 | 10 | - Remove RELATIVE relocations from the .rel.dyn/.rela.dyn section. |
| michael@0 | 11 | - Inject a small code able to apply relative relocations "by hand" |
| michael@0 | 12 | after the .rel.dyn/.rela.dyn section. |
| michael@0 | 13 | - Inject a section containing relocative relocations in a different |
| michael@0 | 14 | and more packed format, after the small code. |
| michael@0 | 15 | - Register the small code as DT_INIT function. Make the small code call |
| michael@0 | 16 | what was initially the DT_INIT function, if there was one. |
| michael@0 | 17 | - Remove the hole between the new section containing relative |
| michael@0 | 18 | relocations and the following sections, adjusting offsets and base |
| michael@0 | 19 | addresses accordingly. |
| michael@0 | 20 | - Adjust PT_LOAD entries to fit new offsets, and add an additional |
| michael@0 | 21 | PT_LOAD entry when that is necessary to handle the discrepancy between |
| michael@0 | 22 | offsets and base addresses, meaning the section offsets may yet again |
| michael@0 | 23 | need adjustments. |
| michael@0 | 24 | - Adjust various DT_* dynamic tags to fit the new ELF layout. |
| michael@0 | 25 | - Adjust section headers. |
| michael@0 | 26 | - Adjust ELF headers. |
| michael@0 | 27 | |
| michael@0 | 28 | See http://glandium.org/blog/?p=1177#relocations for some figures. |
