Monotonic counter as seen from guest is not monotonic

[Samuel Tardieu]

The attached program, which uses the Linux kernel monotonic counter, shows that the counter is not monotonic in a 32 or 64 bits Linux host, at least when the guest is a 64 bits Linux.

Several programs, such as the Ada runtime or the Factor programming language, depend on the fact that the monotonic counter is indeed monotonic.

Tested with:

• Host: Arch Linux 64 bits 2.6.32
• Guest: Arch Linux 32 bits or 64 bits 2.6.32

In the guest, compile and run the test program:

% gcc -O2 -o t t.c -lrt % ./t

After a few seconds at most, the program will exit with an error message, proof of the problem. If it doesn't, then everything is fine (this happens when executed outside of VirtualBox for example).

[Samuel Tardieu]

Source file t.c which demonstrates the problem