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Getting Started with Gem5-CVA6

By Shanzay Wasim

Introduction to GEM5-CVA6

Gem5 is a powerful computer architecture simulator that researchers and developers use to explore and analyze computer system performance. With its highly modular and extensible design, Gem5 provides a flexible platform for studying processor design, memory hierarchies, and system-level interactions. It supports a wide range of systems, from simple uniprocessor machines to complex multicore setups, making it invaluable for both academic research and industry development.

Setting up GEM5-CVA6

Now that you have gotten some basic understanding of what gem5 is, let’s dive into the steps to set up GEM5-CVA6 in your system.

Step 1: Cloning Repositories

   Open your terminal and execute the following commands:


    git clone https://github.com/UmerShahidengr/gem5 gem5_cva6
    git clone https://github.com/darchr/riscv-validation.git

   The darchr/gem5 repo was forked to keep track of changes made when modelling cva6 on the gem5 simulator

Step 2: Changing Directory

   Navigate to the `gem5_cva6` directory:


    cd gem5_cva6

Step 3: Switching Branch

   Switch to the required branch:


    git checkout --track origin/CVA6/riscv-validation

Step 4: Installing Libraries

   Install the necessary libraries with:


    sudo apt-get install build-essential git m4 scons zlib1g zlib1g-dev libprotobuf-dev protobuf-compiler libprotoc-dev libgoogle-perftools-dev python-dev python

   If you encounter errors related to the Python library, resolve them by installing the following:

   To resolve this, install following libraries


    sudo apt-get install python3-dev
    sudo apt-get install python3
    sudo apt-get install build-essential git m4 scons zlib1g zlib1g-dev libprotobuf-dev protobuf-compiler libprotoc-dev libgoogle-perftools-dev python3-dev

Step 5: Compilation

   Compile Gem5 for RISCV in the `gem5_cva6` directory using:


    scons build/RISCV/gem5.opt -j<threads></threads>

   Replace `` with the number of cores in your PC plus one. To check the number of cores, press `Ctrl + Shift + Esc` to open the Task Manager, select the Performance tab, and note the number of cores. For example, if you have 4 cores, replace `<threads>` with 5:


    scons build/RISCV/gem5.opt –j5

   If you receive the error “collect2: fatal error: ld terminated with signal 9 [killed]”, increase the swap space. Check the available swap space with:


    free –h

   To increase swap space, create a `.wslconfig` file with:


    # Settings apply across all Linux distros running on WSL 2
    [wsl2]

    # Sets amount of swap storage space to 8GB, default is 25% of available RAM
    swap=20GB

    # Turn off default connection to bind WSL 2 localhost to Windows localhost
    localhostforwarding=true

   Keep the filepath as:


    <Windows Drive>:\Users\<Username>\.wslconfig

   Check the available swap space:


    free –h

   After creating the file, restart your terminal and recheck the swap space. If the space hasn’t increased, ensure the filename is exactly `.wslconfig`.

Step 6: Checking Host

   Determine whether you are working on a RISCV or non-RISCV host by running:


    uname -m

   If the output is `x86_64`, you are on a non-RISCV host. If the output is `riscv`, you are on a RISCV host. On a non-RISCV host, install the RISCV GCC compiler with: sudo apt install gcc-riscv64-linux-gnu

Step 7: Validation

   Navigate to the `riscv-validation` repository:


    cd riscv-validation

   Note: Ensure you are not in the `gem5_cva6` directory before this step.

Step 8: Compiling Benchmarks

   Compile the benchmarks for RISCV using:


    ./build_benchmarks.sh <C_compiler_name></C_compiler_name>

   Replace <C_compiler_name> with:

  • `riscv64-linux-gnu-gcc` (for non-RISCV hosts)
  • `gcc` (for RISCV hosts)

Step 9: Revisiting Repository

   Return to the `gem5_cva6` directory: 


    cd gem5_cva6

   Note: Make sure you are out of the “riscv-validation” directory before this step.

Step 10: Running Benchmarks

   Run benchmarks on gem5 with:


    ../riscv-validation/scripts/gem5_bench.sh configs/example/gem5_library/cva6-run.py
    ../riscv-validation/microbenchmark_suite-bins 100

   If you are working on WSL (Windows Subsystem for Linux), you may you encounter the “Cannot Allocate Memory” error like shown in figure below:

   To resolve this you need to increase the swap space as described in Step 5.

Step 11: Finalization

   Verify that Gem5 is set up correctly by checking the output:


    cat microbenchmark_suite-out/gem5_microbenchmark_suite.csv

   The output should be as shown in the figure below:

TESTING GEM5

Overview


    daqrcggem5_cva6
    vim configs/example/gem5_library/cva6-run.py
    ls src/python/gem5/prebuilt/cva6/
  1. Run and understand the Hello World file as follows:
    • Go to the <gem5_source> directory (cd gem5_cva6)
    • Type: vim configs/example/hmc_hello.py on the terminal

    This will open the Gem 5 hmc_hello.py file.

  2. Run and understand the cva6-run.py file as follows:
    • Type: vim configs/example/gem5_library/cva6-run.py on the terminal
  3. Study the cva6 .py files:
    • Go to the <gem5_source> directory (cd gem5_cva6)
    • Type: ls src/python/gem5/prebuilt/cva6/ on the terminal

    To open a .py file type vim <path to .pyfile>

    For Example:

    
    vim src/python/gem5/prebuilt/cva6/cva6_board.py

    will open the cva6_board.py file.

  4. Study the CVA6 Core and Draw a block diagram of the Board (with its specs).

Conclusion

You are now ready to work with Gem5 on your PC. If all the testing steps work correctly, your setup is successfully installed. You can start simulating and exploring computer architecture!


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