CPU Core Faker aka Dual Core Fix is a DLL that overrides a few kernel32 functions to give the impression to the
library user that the system has a different number of CPU cores. It was originally developed for Far Cry 4, which
won't load if executed on a CPU with less than four logical cores.
This fix is really generic and could work with other games, there is no FC4 specific code.I've uploaded the source code to CodePlex: https://cpucorefaker.codeplex.com/
There you can find a brief explanation, here are the returned values from Dual Core Fix v1/v2/v3:API function / Original (DC) / DC Fix v3 / DC Fix v2 / DC Fix v1
---------------------------------------------------------------------
[GetSystemInfo]
> dwNumberOfProcessors / 2 / 8 / 4 / 8
> dwActiveProcessorMask / 3 / 255 / unmodified / unmodified
---------------------------------------------------------------------
[setThreadAffinityMask]
mask > actual mak / (1,2,3) / 3 (actual max) / 3 / 3
mask <= actual max / mask / 3 / mask / 3
---------------------------------------------------------------------
[GetLogicalProcessorInformation]
As described in "documentation"
---------------------------------------------------------------------The code contains some C++11 features so compile with VS2013. You'll also need EasyHook.

doesnt handle cpuid opcode though?

doesnt handle cpuid opcode though?

Its a user level(ring 3) hook . To change behavior of  "opcode"s you will need virtualization support and some form of kernel hooks. Check paravirtualization topics if you are interested.