Object code relocation and Intel Pin interaction

Question

I am working on a multiprocessor architectural simulator that uses Intel Pin to instrument C++ executable binaries and report interesting events (e.g., some function calls, thread create/finish, etc.). Basically, I build an instruction-decode cache of all instructions when their images are loaded and analyze instruction execution afterwards. So it is important for instruction addresses at image-load time to be the same as (or at least get updated synchronously with) instruction addresses at run-time.

Intel Pin API (e.g., IMG_AddInstrumentFunction) enables me to get information about the loaded images (executables and shared libraries) such as entry points, low/high address, etc.

However, I noticed that the instrumented program executes instructions at addresses that do not belong to any of the loaded images. By inspection, I am suspecting that the dynamic loader (image /lib64/ld-linux-x86-64.so.2 on 64-bit Centos 6.3) is relocating the main executable in memory by calling routine _dl_relocate_object.

I understand the need for relocatable code and all that stuff. I just need pointers to a good documentation (or just a brief description/advice) on how/when these relocations might happen (at load-time and runtime) so that I can take them into account in my architectural simulator. In other words, the mechanism used to achieve it (library functions that I need to instrument, conditions, or maybe randomization if there is any, g++ compiler switches that can be used to suppress relocation, etc). P.S.: I am only targeting x86/x86_64 architectures

Answer 1

Relocation are processor specific, so ARM and x86-64 and x86 have different relocations (because their instruction set is different).

^{Relocation are also operating system specific, but some related OSes try to have the same relocations, e.g. Solaris and Linux for x86-64}

They are described in detail in the ABI (application binary interface) specification "System V Application Binary Interface AMD64 Architecture Processor Supplement". The original x86-64 ABI used to be on http://www.x86-64.org/documentation.html but that site is not responding since several weeks. An old copy is on this link and a newer one is here

There is also the X32 ABI

See also this question.