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   <dl>
   <dt>authors</dt>
   <dd>Jason Lowe-Power</dd>
 </dl>

 <h1 id="building-gem5">Building gem5</h1>

 <p>This chapter covers the details of how to set up a gem5 developmment
 environment and build gem5.</p>

 <h2 id="requirements-for-gem5">Requirements for gem5</h2>

 <p>See <a href="http://gem5.org/Compiling_M5#Required_Software">gem5 requirements</a>
 for more details.</p>

 <p>On Ubuntu, you can install all of the required dependencies with the
 following command. The requirements are detailed below.</p>

 <p>``` {.sourceCode .sh}
 sudo apt install build-essential git m4 scons zlib1g zlib1g-dev libprotobuf-dev protobuf-compiler libprotoc-dev libgoogle-perftools-dev python-dev python</p>
 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>
 1.  git ([Git](https://git-scm.com/)):
     :   The gem5 project uses [Git](https://git-scm.com/) for version
         control. [Git](https://git-scm.com/) is a distributed version
         control system. More information about
         [Git](https://git-scm.com/) can be found by following the link.
         Git should be installed by default on most platforms. However,
         to install Git in Ubuntu use

         ``` {.sourceCode .sh}
         sudo apt-get install git
         ```

 2.  gcc 4.8+
     :   You may need to use environment variables to point to a
         non-default version of gcc.

         On Ubuntu, you can install a development environment with

         ``` {.sourceCode .sh}
         sudo apt-get install build-essential
         ```

 3.  [SCons](http://www.scons.org/)
     :   gem5 uses SCons as its build environment. SCons is like make on
         steroids and uses Python scripts for all aspects of the build
         process. This allows for a very flexible (if slow) build system.

         To get SCons on Ubuntu use

         ``` {.sourceCode .sh}
         sudo apt-get install scons
         ```

 4.  Python 2.7+
     :   gem5 relies on the Python development libraries. To install
         these on Ubuntu use

         ``` {.sourceCode .sh}
         sudo apt-get install python-dev
         ```

 5.  [protobuf](https://developers.google.com/protocol-buffers/) 2.1+
     :   "Protocol buffers are a language-neutral, platform-neutral
         extensible mechanism for serializing structured data." In gem5,
         the [protobuf](https://developers.google.com/protocol-buffers/)
         library is used for trace generation and playback.
         [protobuf](https://developers.google.com/protocol-buffers/) is
         not a required package, unless you plan on using it for trace
         generation and playback.

         ``` {.sourceCode .sh}
         sudo apt-get install libprotobuf-dev python-protobuf protobuf-compiler libgoogle-perftools-dev
         ```

 Getting the code
 ----------------

 Change directories to where you want to download the gem5 source. Then,
 to clone the repository, use the `git clone` command.

 ``` {.sourceCode .sh}
 git clone https://gem5.googlesource.com/public/gem5
 </code></pre></div></div>

 <p>You can now change directories to <code class="highlighter-rouge">gem5</code> which contains all of the gem5
 code.</p>

 <h2 id="your-first-gem5-build">Your first gem5 build</h2>

 <p>Let’s start by building a basic x86 system. Currently, you must compile
 gem5 separately for every ISA that you want to simulate. Additionally,
 if using ruby-intro-chapter, you have to have separate compilations for
 every cache coherence protocol.</p>

 <p>To build gem5, we will use SCons. SCons uses the SConstruct file
 (<code class="highlighter-rouge">gem5/SConstruct</code>) to set up a number of variables and then uses the
 SConscript file in every subdirectory to find and compile all of the
 gem5 source.</p>

 <p>SCons automatically creates a <code class="highlighter-rouge">gem5/build</code> directory when first
 executed. In this directory you’ll find the files generated by SCons,
 the compiler, etc. There will be a separate directory for each set of
 options (ISA and cache coherence protocol) that you use to compile gem5.</p>

 <p>There are a number of default compilations options in the <code class="highlighter-rouge">build_opts</code>
 directory. These files specify the parameters passed to SCons when
 initially building gem5. We’ll use the X86 defaults and specify that we
 want to compile all of the CPU models. You can look at the file
 <code class="highlighter-rouge">build_opts/X86</code> to see the default values for the Scons options. You
 can also specify these options on the command line to override any
 default.</p>

 <p>``` {.sourceCode .sh}
 scons build/X86/gem5.opt -j9</p>
 <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>
 &gt; **gem5 binary types**
 &gt;
 &gt; The SCons scripts in gem5 currently have 5 different binaries you can
 &gt; build for gem5: debug, opt, fast, prof, and perf. These names are
 &gt; mostly self-explanatory, but detailed below.
 &gt;
 &gt; debug
 &gt; :   Built with no optimizations and debug symbols. This binary is
 &gt;     useful when using a debugger to debug if the variables you need to
 &gt;     view are optimized out in the opt version of gem5. Running with
 &gt;     debug is slow compared to the other binaries.
 &gt;
 &gt; opt
 &gt; :   This binary is build with most optimizations on (e.g., -O3), but
 &gt;     with debug symbols included. This binary is much faster than
 &gt;     debug, but still contains enough debug information to be able to
 &gt;     debug most problems.
 &gt;
 &gt; fast
 &gt; :   Built with all optimizations on (including link-time optimizations
 &gt;     on supported platforms) and with no debug symbols. Additionally,
 &gt;     any asserts are removed, but panics and fatals are still included.
 &gt;     fast is the highest performing binary, and is much smaller than
 &gt;     opt. However, fast is only appropriate when you feel that it is
 &gt;     unlikely your code has major bugs.
 &gt;
 &gt; prof and perf
 &gt; :   These two binaries are build for profiling gem5. prof includes
 &gt;     profiling information for the GNU profiler (gprof), and perf
 &gt;     includes profiling information for the Google performance tools
 &gt;     (gperftools).
 &gt;
 The main argument passed to SCons is what you want to build,
 `build/X86/gem5.opt`. In this case, we are building gem5.opt (an
 optimized binary with debug symbols). We want to build gem5 in the
 directory build/X86. Since this directory currently doesn't exist, SCons
 will look in `build_opts` to find the default parameters for X86. (Note:
 I'm using -j9 here to execute the build on 9 of my 8 cores on my
 machine. You should choose an appropriate number for your machine,
 usually cores+1.)

 The output should look something like below:

     Checking for C header file Python.h... yes
     Checking for C library pthread... yes
     Checking for C library dl... yes
     Checking for C library util... yes
     Checking for C library m... yes
     Checking for C library python2.7... yes
     Checking for accept(0,0,0) in C++ library None... yes
     Checking for zlibVersion() in C++ library z... yes
     Checking for GOOGLE_PROTOBUF_VERIFY_VERSION in C++ library protobuf... yes
     Checking for clock_nanosleep(0,0,NULL,NULL) in C library None... yes
     Checking for timer_create(CLOCK_MONOTONIC, NULL, NULL) in C library None... no
     Checking for timer_create(CLOCK_MONOTONIC, NULL, NULL) in C library rt... yes
     Checking for C library tcmalloc... yes
     Checking for backtrace_symbols_fd((void*)0, 0, 0) in C library None... yes
     Checking for C header file fenv.h... yes
     Checking for C header file linux/kvm.h... yes
     Checking size of struct kvm_xsave ... yes
     Checking for member exclude_host in struct perf_event_attr...yes
     Building in /local.chinook/gem5/gem5-tutorial/gem5/build/X86
     Variables file /local.chinook/gem5/gem5-tutorial/gem5/build/variables/X86 not found,
       using defaults in /local.chinook/gem5/gem5-tutorial/gem5/build_opts/X86
     scons: done reading SConscript files.
     scons: Building targets ...
      [ISA DESC] X86/arch/x86/isa/main.isa -&gt; generated/inc.d
      [NEW DEPS] X86/arch/x86/generated/inc.d -&gt; x86-deps
      [ENVIRONS] x86-deps -&gt; x86-environs
      [     CXX] X86/sim/main.cc -&gt; .o
      ....
      .... &lt;lots of output&gt;
      ....
      [   SHCXX] nomali/lib/mali_midgard.cc -&gt; .os
      [   SHCXX] nomali/lib/mali_t6xx.cc -&gt; .os
      [   SHCXX] nomali/lib/mali_t7xx.cc -&gt; .os
      [      AR]  -&gt; drampower/libdrampower.a
      [   SHCXX] nomali/lib/addrspace.cc -&gt; .os
      [   SHCXX] nomali/lib/mmu.cc -&gt; .os
      [  RANLIB]  -&gt; drampower/libdrampower.a
      [   SHCXX] nomali/lib/nomali_api.cc -&gt; .os
      [      AR]  -&gt; nomali/libnomali.a
      [  RANLIB]  -&gt; nomali/libnomali.a
      [     CXX] X86/base/date.cc -&gt; .o
      [    LINK]  -&gt; X86/gem5.opt
     scons: done building targets.

 When compilation is finished you should have a working gem5 executable
 at `build/X86/gem5.opt`. The compilation can take a very long time,
 often 15 minutes or more, especially if you are compiling on a remote
 file system like AFS or NFS.

 Common errors
 -------------

 ### Wrong gcc version

     Error: gcc version 4.8 or newer required.
            Installed version: 4.4.7

 Update your environment variables to point to the right gcc version, or
 install a more up to date version of gcc. See
 building-requirements-section.

 ### Python in a non-default location

 If you use a non-default version of Python, (e.g., version 2.7 when 2.5
 is your default), there may be problems when using SCons to build gem5.
 RHEL6 version of SCons uses a hardcoded location for Python, which
 causes the issue. gem5 often builds successfully in this case, but may
 not be able to run. Below is one possible error you may see when you run
 gem5.

     Traceback (most recent call last):
       File "........../gem5-stable/src/python/importer.py", line 93, in &lt;module&gt;
         sys.meta_path.append(importer)
     TypeError: 'dict' object is not callable

 To fix this, you can force SCons to use your environment's Python
 version by running `` python `which scons` build/X86/gem5.opt `` instead
 of `scons build/X86/gem5.opt`. More information on this can be found on
 the gem5 wiki about non-default Python locations: [Using a non-default
 Python
 installation](http://www.gem5.org/Using_a_non-default_Python_installation).

 ### M4 macro processor not installed

 If the M4 macro processor isn't installed you'll see an error similar to
 this:

     ...
     Checking for member exclude_host in struct perf_event_attr...yes
     Error: Can't find version of M4 macro processor.  Please install M4 and try again.

 Just installing the M4 macro package may not solve this issue. You may
 nee to also install all of the `autoconf` tools. On Ubuntu, you can use
 the following command.

 ``` {.sourceCode .sh}
 sudo apt-get install automake
 </code></pre></div></div>


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	<a class="subitem " href="/events">Event-driven programming</a>

	<a class="subitem " href="/parameters">Adding parameters to SimObjects and more events</a>

	<a class="subitem " href="/memoryobject">Creating SimObjects in the memory system</a>

	<a class="subitem " href="/simplecache">Creating a simple cache object</a>

	</div>

	<a class="item" data-toggle="collapse" href="#pt3" role="button" aria-expanded="false" aria-controls="collapseExample">
	Modeling Cache Coherence with Ruby
	</a>
	<div class="collapse " id="pt3">

	<a class="subitem " href="/intro">Introduction to Ruby</a>

	<a class="subitem " href="/cache-intro">MSI example cache protocol</a>

	<a class="subitem " href="/cache-declarations">Declaring a state machine</a>

	<a class="subitem " href="/cache-in-ports">In port code blocks</a>

	<a class="subitem " href="/cache-actions">Action code blocks</a>

	<a class="subitem " href="/cache-transitions">Transition code blocks</a>

	<a class="subitem " href="/directory">MSI Directory implementation</a>

	<a class="subitem " href="/MSIbuilding">Compiling a SLICC protocol</a>

	<a class="subitem " href="/configuration">Configuring a simple Ruby system</a>

	<a class="subitem " href="/running">Running the simple Ruby system</a>

	<a class="subitem " href="/MSIdebugging">Debugging SLICC Protocols</a>

	<a class="subitem " href="/simple-MI_example">Configuring for a standard protocol</a>

	</div>

	</div>

	<div class="container" id="doc-container">

	<!-- <h1>Building</h1> -->
	<dl>
	<dt>authors</dt>
	<dd>Jason Lowe-Power</dd>
	</dl>

	<h1 id="building-gem5">Building gem5</h1>

	<p>This chapter covers the details of how to set up a gem5 developmment
	environment and build gem5.</p>

	<h2 id="requirements-for-gem5">Requirements for gem5</h2>

	<p>See <a href="http://gem5.org/Compiling_M5#Required_Software">gem5 requirements</a>
	for more details.</p>

	<p>On Ubuntu, you can install all of the required dependencies with the
	following command. The requirements are detailed below.</p>

	<p>``` {.sourceCode .sh}
	sudo apt install build-essential git m4 scons zlib1g zlib1g-dev libprotobuf-dev protobuf-compiler libprotoc-dev libgoogle-perftools-dev python-dev python</p>
	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>
	1. git ([Git](https://git-scm.com/)):
	: The gem5 project uses [Git](https://git-scm.com/) for version
	control. [Git](https://git-scm.com/) is a distributed version
	control system. More information about
	[Git](https://git-scm.com/) can be found by following the link.
	Git should be installed by default on most platforms. However,
	to install Git in Ubuntu use

	``` {.sourceCode .sh}
	sudo apt-get install git
	```

	2. gcc 4.8+
	: You may need to use environment variables to point to a
	non-default version of gcc.

	On Ubuntu, you can install a development environment with

	``` {.sourceCode .sh}
	sudo apt-get install build-essential
	```

	3. [SCons](http://www.scons.org/)
	: gem5 uses SCons as its build environment. SCons is like make on
	steroids and uses Python scripts for all aspects of the build
	process. This allows for a very flexible (if slow) build system.

	To get SCons on Ubuntu use

	``` {.sourceCode .sh}
	sudo apt-get install scons
	```

	4. Python 2.7+
	: gem5 relies on the Python development libraries. To install
	these on Ubuntu use

	``` {.sourceCode .sh}
	sudo apt-get install python-dev
	```

	5. [protobuf](https://developers.google.com/protocol-buffers/) 2.1+
	: "Protocol buffers are a language-neutral, platform-neutral
	extensible mechanism for serializing structured data." In gem5,
	the [protobuf](https://developers.google.com/protocol-buffers/)
	library is used for trace generation and playback.
	[protobuf](https://developers.google.com/protocol-buffers/) is
	not a required package, unless you plan on using it for trace
	generation and playback.

	``` {.sourceCode .sh}
	sudo apt-get install libprotobuf-dev python-protobuf protobuf-compiler libgoogle-perftools-dev
	```

	Getting the code
	----------------

	Change directories to where you want to download the gem5 source. Then,
	to clone the repository, use the `git clone` command.

	``` {.sourceCode .sh}
	git clone https://gem5.googlesource.com/public/gem5
	</code></pre></div></div>

	<p>You can now change directories to <code class="highlighter-rouge">gem5</code> which contains all of the gem5
	code.</p>

	<h2 id="your-first-gem5-build">Your first gem5 build</h2>

	<p>Let’s start by building a basic x86 system. Currently, you must compile
	gem5 separately for every ISA that you want to simulate. Additionally,
	if using ruby-intro-chapter, you have to have separate compilations for
	every cache coherence protocol.</p>

	<p>To build gem5, we will use SCons. SCons uses the SConstruct file
	(<code class="highlighter-rouge">gem5/SConstruct</code>) to set up a number of variables and then uses the
	SConscript file in every subdirectory to find and compile all of the
	gem5 source.</p>

	<p>SCons automatically creates a <code class="highlighter-rouge">gem5/build</code> directory when first
	executed. In this directory you’ll find the files generated by SCons,
	the compiler, etc. There will be a separate directory for each set of
	options (ISA and cache coherence protocol) that you use to compile gem5.</p>

	<p>There are a number of default compilations options in the <code class="highlighter-rouge">build_opts</code>
	directory. These files specify the parameters passed to SCons when
	initially building gem5. We’ll use the X86 defaults and specify that we
	want to compile all of the CPU models. You can look at the file
	<code class="highlighter-rouge">build_opts/X86</code> to see the default values for the Scons options. You
	can also specify these options on the command line to override any
	default.</p>

	<p>``` {.sourceCode .sh}
	scons build/X86/gem5.opt -j9</p>
	<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>
	> gem5 binary types
	>
	> The SCons scripts in gem5 currently have 5 different binaries you can
	> build for gem5: debug, opt, fast, prof, and perf. These names are
	> mostly self-explanatory, but detailed below.
	>
	> debug
	> : Built with no optimizations and debug symbols. This binary is
	> useful when using a debugger to debug if the variables you need to
	> view are optimized out in the opt version of gem5. Running with
	> debug is slow compared to the other binaries.
	>
	> opt
	> : This binary is build with most optimizations on (e.g., -O3), but
	> with debug symbols included. This binary is much faster than
	> debug, but still contains enough debug information to be able to
	> debug most problems.
	>
	> fast
	> : Built with all optimizations on (including link-time optimizations
	> on supported platforms) and with no debug symbols. Additionally,
	> any asserts are removed, but panics and fatals are still included.
	> fast is the highest performing binary, and is much smaller than
	> opt. However, fast is only appropriate when you feel that it is
	> unlikely your code has major bugs.
	>
	> prof and perf
	> : These two binaries are build for profiling gem5. prof includes
	> profiling information for the GNU profiler (gprof), and perf
	> includes profiling information for the Google performance tools
	> (gperftools).
	>
	The main argument passed to SCons is what you want to build,
	`build/X86/gem5.opt`. In this case, we are building gem5.opt (an
	optimized binary with debug symbols). We want to build gem5 in the
	directory build/X86. Since this directory currently doesn't exist, SCons
	will look in `build_opts` to find the default parameters for X86. (Note:
	I'm using -j9 here to execute the build on 9 of my 8 cores on my
	machine. You should choose an appropriate number for your machine,
	usually cores+1.)

	The output should look something like below:

	Checking for C header file Python.h... yes
	Checking for C library pthread... yes
	Checking for C library dl... yes
	Checking for C library util... yes
	Checking for C library m... yes
	Checking for C library python2.7... yes
	Checking for accept(0,0,0) in C++ library None... yes
	Checking for zlibVersion() in C++ library z... yes
	Checking for GOOGLE_PROTOBUF_VERIFY_VERSION in C++ library protobuf... yes
	Checking for clock_nanosleep(0,0,NULL,NULL) in C library None... yes
	Checking for timer_create(CLOCK_MONOTONIC, NULL, NULL) in C library None... no
	Checking for timer_create(CLOCK_MONOTONIC, NULL, NULL) in C library rt... yes
	Checking for C library tcmalloc... yes
	Checking for backtrace_symbols_fd((void*)0, 0, 0) in C library None... yes
	Checking for C header file fenv.h... yes
	Checking for C header file linux/kvm.h... yes
	Checking size of struct kvm_xsave ... yes
	Checking for member exclude_host in struct perf_event_attr...yes
	Building in /local.chinook/gem5/gem5-tutorial/gem5/build/X86
	Variables file /local.chinook/gem5/gem5-tutorial/gem5/build/variables/X86 not found,
	using defaults in /local.chinook/gem5/gem5-tutorial/gem5/build_opts/X86
	scons: done reading SConscript files.
	scons: Building targets ...
	[ISA DESC] X86/arch/x86/isa/main.isa -> generated/inc.d
	[NEW DEPS] X86/arch/x86/generated/inc.d -> x86-deps
	[ENVIRONS] x86-deps -> x86-environs
	[ CXX] X86/sim/main.cc -> .o
	....
	.... <lots of output>
	....
	[ SHCXX] nomali/lib/mali_midgard.cc -> .os
	[ SHCXX] nomali/lib/mali_t6xx.cc -> .os
	[ SHCXX] nomali/lib/mali_t7xx.cc -> .os
	[ AR] -> drampower/libdrampower.a
	[ SHCXX] nomali/lib/addrspace.cc -> .os
	[ SHCXX] nomali/lib/mmu.cc -> .os
	[ RANLIB] -> drampower/libdrampower.a
	[ SHCXX] nomali/lib/nomali_api.cc -> .os
	[ AR] -> nomali/libnomali.a
	[ RANLIB] -> nomali/libnomali.a
	[ CXX] X86/base/date.cc -> .o
	[ LINK] -> X86/gem5.opt
	scons: done building targets.

	When compilation is finished you should have a working gem5 executable
	at `build/X86/gem5.opt`. The compilation can take a very long time,
	often 15 minutes or more, especially if you are compiling on a remote
	file system like AFS or NFS.

	Common errors
	-------------

	### Wrong gcc version

	Error: gcc version 4.8 or newer required.
	Installed version: 4.4.7

	Update your environment variables to point to the right gcc version, or
	install a more up to date version of gcc. See
	building-requirements-section.

	### Python in a non-default location

	If you use a non-default version of Python, (e.g., version 2.7 when 2.5
	is your default), there may be problems when using SCons to build gem5.
	RHEL6 version of SCons uses a hardcoded location for Python, which
	causes the issue. gem5 often builds successfully in this case, but may
	not be able to run. Below is one possible error you may see when you run
	gem5.

	Traceback (most recent call last):
	File "........../gem5-stable/src/python/importer.py", line 93, in <module>
	sys.meta_path.append(importer)
	TypeError: 'dict' object is not callable

	To fix this, you can force SCons to use your environment's Python
	version by running `` python `which scons` build/X86/gem5.opt `` instead
	of `scons build/X86/gem5.opt`. More information on this can be found on
	the gem5 wiki about non-default Python locations: [Using a non-default
	Python
	installation](http://www.gem5.org/Using_a_non-default_Python_installation).

	### M4 macro processor not installed

	If the M4 macro processor isn't installed you'll see an error similar to
	this:

	...
	Checking for member exclude_host in struct perf_event_attr...yes
	Error: Can't find version of M4 macro processor. Please install M4 and try again.

	Just installing the M4 macro package may not solve this issue. You may
	nee to also install all of the `autoconf` tools. On Ubuntu, you can use
	the following command.

	``` {.sourceCode .sh}
	sudo apt-get install automake
	</code></pre></div></div>


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