How to Build ARM Kernels for gem5 Simulator Step by Step

Summary

Sources

gem5.org

In the evolving landscape of computer architecture research, the ability to simulate and test different hardware configurations is invaluable. The gem5 simulator stands as a cutting-edge tool in this domain, and a key component of utilizing gem5 effectively is the ARM kernel. The ARM kernel is the heart of the operating system, responsible for managing hardware resources and enabling software applications to run efficiently on ARM-based systems. This segment will explore the meticulous process of building an ARM kernel tailored for gem5, illuminating the steps required to compile a kernel from scratch. To embark on this intricate journey, certain prerequisites must be established. For those aiming to run headless systems, akin to server-style setups devoid of a graphical frame-buffer, you must first acquire ARM cross compilers and the device tree compiler. In the context of an x86 host machine, users with up-to-date versions of Ubuntu or Debian can conveniently install the necessary software using the package manager with the following command: ``` apt-get install gcc-arm-linux-gnueabihf gcc-aarch64-linux-gnu device-tree-compiler ``` For those who cannot avail themselves of these pre-packaged compilers, an alternative path involves downloading the compilers directly from ARMs official resources, taking care to ensure that the binaries are included in the users PATH. With the cross compilers in place, attention turns to the kernel source. The source for ARM kernels compatible with gem5 can be obtained through a clone operation from the official gem5 repository. The repository is meticulously organized with tags corresponding to different kernel releases and branches that align with major Linux revisions. The following command is used to clone the kernel: ``` git clone https://gem5.googlesource.com/arm/linux ``` Post-cloning, users may select the desired release branch or kernel version. For instance, to switch to the v4.14 branch of the kernel, one would execute: ``` git checkout -b gem5/v4.14 ``` The build process itself is straightforward yet commands precision. Within the kernel repository, the user initiates the compilation with the following sequence of commands, adjusting the ARCH and CROSS_COMPILE variables as per the systems architecture, be it AArch32 or AArch64: ``` make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- gem5_defconfig make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- -j `nproc` ``` These commands configure the kernel with default settings for gem5 and then compile the kernel utilizing all available processor cores to expedite the process. Upon successful compilation, the kernels functionality is put to the test using gem5s bootloader. The bootloader, which comes in two variants tailored for 32-bit and 64-bit kernels respectively, is compiled with commands specific to each architecture. For a 32-bit kernel, the command is as follows: ``` make -C system/arm/bootloader/arm ``` For a 64-bit kernel, the corresponding command is: ``` make -C system/arm/bootloader/arm64 ``` The final component in the kernel build process is the Device Tree Blob, commonly referred to as the DTB. The DTB plays a critical role in defining the hardware layout to the operating system. While gem5 ships with DTB files, users are encouraged to generate them on the fly unless modifications are needed. The command to build the DTB files is: ``` make -C system/arm/dt ``` However, for users who do not require customized hardware descriptions, it is recommended to leverage DTB autogeneration. By executing a Full System (FS) script without specifying the `todtb` option, gem5 will dynamically create the DTB based on the instantiated platform. In summary, the process of building an ARM kernel for gem5 involves setting up the appropriate cross compilers, obtaining the kernel source, and executing a series of commands to compile both the kernel and its bootloader. With the options of pre-built kernels and autogeneration of DTBs, users are provided with flexibility and ease in their kernel configuration endeavors. Through these steps, researchers and developers can harness the full potential of gem5 to simulate and explore the vast possibilities within ARM-based systems.