Getting started with gem5 development

Why develop gem5?

• Add new models
• Extend current models
• Fix things and contribute back!

A bit about the difference between C++ and python

• The models are in C++
• The parameters that you can change are declared in src/, but in a “python” file (SimObject description file)

• You have an “instance” or “configuration” which sets the parameters.

• An analogy
  • The model is “An out of order CPU”
  • The parameters are the size of the reorder buffer and the issue width
  • The “instance” or “configuration” is an i7-7700

What is a SimObject?

• Main thing that gem5 uses as the bridge from the C++ models to the python configuration
• Things in src/ and in the SimObjects should be the model not the configuration.

gem5’s event queue

• A bit about event-driven programming
• What it means for events to execute
• Relation between SimObjects and events

Building gem5

• Dependencies
• Build system: SCons
• Build parameters
  • Two types: gem5 features and compiler parameters
  • Opt/fast, profiling, linker
  • ISA, GPU, Ruby protocol, others

Making modifications and using git

• Install the hooks!
• Use the style checker! Don’t ignore it!
• Create a branch for yourself
• Use good commit messages… it’s worth the time!

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