Results under sde64 different from results without sde64.

[philiprbrenan]

Please tell me why (in the above) I get a different result running a program under the sde64 emulator than I do without the emulator?  The emulator response is the expected one.  Thanks!

[AdyT_Intel]

It is hard to tell why there are differences between native run and emulated run.
The main differences is the emulation of the CPUID and XSAVE instructions. 
Currently, when Intel SDE is run without a chip knob (like in your example) it defaults to the Icelake CPU model.

Please note that Intel SDE does not emulate (most of the) instructions supported by the running CPU.

[philiprbrenan · Accepted solution]

The code calls Syscall 1 to write the registers contents to the screen.  This call appears to disturb register 11 on Ubuntu 20.  This behavior is not reflected by sde64. Hence the difference.

[AdyT_Intel]

Intel SDE is based on binary instrumentation technology. This means that the application is undergo translation and registers might have different values then the values in the original run. The translation process makes sure that these changes are isolated from the application, but it is not perfect. There are certain cases where these changes can be leaked/observed by the application.

In your case, before executing a system call, pin (our binary instrumentation system) preserves only part of the registers and not all, and I think that r11 is not preserved in this case.