Linux Kernel Module Cheat

38.13.3.1. gem5 worktree

--gem5-build-id goes a long way, but if you want to seamlessly switch between two gem5 tress without checking out multiple times, then --gem5-worktree is for you.

# Build gem5 at the revision in the gem5 submodule.
./build-gem5

# Create a branch at the same revision as the gem5 submodule.
./build-gem5 --gem5-worktree my-new-feature
cd "$(./getvar --gem5-worktree my-new-feature)"
vim create-bugs
git add .
git commit -m 'Created a bug'
cd -
./build-gem5 --gem5-worktree my-new-feature

# Run the submodule.
./run --emulator gem5 --run-id 0 &>/dev/null &

# Run the branch the need to check out anything.
# With --gem5-worktree, we can do both runs at the same time!
./run --emulator gem5 --gem5-worktree my-new-feature --run-id 1 &>/dev/null &

--gem5-worktree <worktree-id> automatically creates:

a Git worktree of gem5 if one didn’t exit yet for <worktree-id>
a separate build directory, exactly like --gem5-build-id my-new-feature would

We promise that the scripts sill never touch that worktree again once it has been created: it is now up to you to manage the code manually.

--gem5-worktree is required if you want to do multiple simultaneous runs of different gem5 versions, because each gem5 build needs to use the matching Python scripts inside the source tree.

The difference between --gem5-build-id and --gem5-worktree is that --gem5-build-id specifies only the gem5 build output directory, while --gem5-worktree specifies the source input directory.

Each Git worktree needs a branch name, and we append the wt/ prefix to the --gem5-worktree value, where wt stands for WorkTree. This is done to allow us to checkout to a test some-branch branch under submodules/gem5 and still use --gem5-worktree some-branch, without conflict for the worktree branch, which can only be checked out once.