Added function to calculate and encode relative operands

[mappzor]

Related to 268 and #345.

This PR introduces ZydisEncoderEncodeInstructionAbsolute function which accepts absolute addresses instead of:

• RIP-relative operands (base is still EIP/RIP, displacement should contain absolute address)
• relative immediates in branching instructions

First group of instructions is handled by patching displacement after encoding. Second group uses fast size prediction algorithm to find the right variant and calculate relative operand prior to encoding. This has less overhead than trying to brute-force encode different variants. Solutions exploits simplicity of branching instructions as they have less "moving parts" such as prefixes, ModR/M, SIB, etc. This allows for fast table lookups with some minor adjustments.

Let me know if you have any feedback. If we want to proceed with this solution I will clean up my test code and add it to this PR. Final test suite would be a small C tool triggered from usual python test scripts.

[mappzor]

Pushed some tests, CI fails because I cannot commit workflow change:

       - name: Running regression tests (encoder)
         run: |
           cd tests
-          python3 regression_encoder.py ../build/ZydisFuzzReEncoding ../build/ZydisFuzzEncoder
+          python3 regression_encoder.py ../build/ZydisFuzzReEncoding ../build/ZydisFuzzEncoder ../build/ZydisTestEncoderAbsolute

[flobernd]

Thanks a lot @mappzor 👍

I just pushed the workflow changes. There seems to be a minor string format issue, but other than that it looks very good 🙂

[flobernd]

LGTM! Thanks again, that will make a lot of users happy!

Is there a python script to generate the new .inc file or was it rather "generated" by hand? 😄

[mappzor]

There's a new mode added to the script, will push it in a moment. It's not the prettiest thing but it does the job.

[athre0z]

LGTM as well, thanks a lot for tackling this!