search

GaloisInc / macaw

Open source binary analysis tools.
BSD 3-Clause "New" or "Revised" License
205 stars 21 forks source link

Support R_X86_64_COPY #47

Open joehendrix opened 5 years ago

joehendrix commented 5 years ago

Elf relocations of type R_X86_64_COPY are used in dynamic binaries that reference variables defined in shared libraries. We should add support for these, but it may be a bit tricky.

The variables are stored in the binary's .bss section, and so the relocation target is within the .bss section for the binary. These relocations can be used to tell us that address is used to store a given global variable, and this information may be of use in LLVM generation or other binaries transformations.

A couple references that describe this are https://www.cs.stevens.edu/~jschauma/631/elf.html and https://stac47.github.io/c/relocation/elf/tutorial/2018/03/01/understanding-relocation-elf.html.

In addition to adding support, test cases should be written to validate the understanding.

simonjwinwood commented 2 years ago

This is the updated link: https://stevens.netmeister.org/631/elf.html

One problem with the R_X86_64_COPY relocation is that the size of the relocation depends on the size of the symbol. This relocation is used to copy the value of an initialised variable into the location in the binary where it lives --- the dynamic library will have a copy of the variable which is the source of the copy.