Workload generation in FireSim is handled by a tool called FireMarshal in firesim/sw/firesim-software/.

Workloads in FireMarshal consist of a series of Jobs that are assigned to logical nodes in the target system. If no jobs are specified, then the workload is considered uniform and only a single image will be produced for all nodes in the system. Workloads are described by a json file and a corresponding workload directory and can inherit their definitions from existing workloads. Typically, workload configurations are kept in sw/firesim-software/workloads/ although you can use any directory you like. We provide a few basic workloads to start with including buildroot or Fedora-based linux distributions and bare-metal.

Once you define a workload, the marshal command will produce a corresponding boot-binary and rootfs for each job in the workload. This binary and rootfs can then be launched on qemu or spike (for functional simulation), or installed to firesim for running on real RTL.

For more information, see the official FireMarshal documentation, and its quickstart tutorial.