1. Problem

While using CommMonitor in Gem5, the following error message prompted.

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/yulistic/simulators/gem5/src/python/m5/main.py", line 388, in main
    exec filecode in scope
  File "configs/example/se_spec2006.py", line 285, in <module>
    system.monitor = CommMonitor(trace_file=trace_filename)
NameError: name 'CommMonitor' is not defined

2. Cause

The error was because of absence of protobuf. When scon tried to compile CommMonitor, it checks whether the protobuf is installed or not. If it is not installed, scon skip CommMonitor compilation, so we cannot use it.

You can check warning messages which are prompted as yellow characters while building Gem5.

yulistic@machine1:~/simulators/gem5$ scons build/X86/gem5.opt
scons: Reading SConscript files ...
Package protobuf was not found in the pkg-config search path.
Perhaps you should add the directory containing `protobuf.pc'
to the PKG_CONFIG_PATH environment variable
No package 'protobuf' found
Warning: pkg-config could not get protobuf flags.
Checking for leading underscore in global variables...(cached) no
Checking for C header file Python.h... (cached) yes
Checking for C library pthread... (cached) yes
Checking for C library dl... (cached) yes
Checking for C library util... (cached) yes
Checking for C library m... (cached) yes
Checking for C library python2.7... (cached) yes
Checking for accept(0,0,0) in C++ library None... (cached) yes
Checking for zlibVersion() in C++ library z... (cached) yes
Checking for GOOGLE_PROTOBUF_VERIFY_VERSION in C++ library protobuf... no
Warning: did not find protocol buffer library and/or headers.
       Please install libprotobuf-dev for tracing support.

 3. Solution

1) Download source package of protobuf from the site.

2) Install protobuf. Refer to the README file in the package.

3) Type command protoc that is a command for protocbuf compiler to check whether installation is completed.

4) If you get an error message like below, do

sudo ldconfig

or

export LD_LIBRARY_PATH=/usr/local/lib

5) After completing the installation of protobuf, rebuild gem5.

scons build/X86/gem5.opt

It will not prompt warning message related to protobuf any more.