What is the input of the git signing?

We can see the signature by "git cat-file -p COMMMIT_ID". What is the input of the signing? The commit file content? The tree of the commit? The blobs of all?

I have not found any document about this.

https://stackoverflow.com/questions/66978819/what-is-the-input-of-the-git-signing April 07, 2021 at 10:33AM