Download latest PDF: https://gitlab.com/x86-psABIs/x86-64-ABI/-/jobs/artifacts/master/raw/x86-64-ABI/abi.pdf?job=build
These are the ELF x86-64 psABI LaTeX sources including full history from the former subversion repository at svn.x86-64.org, which is gone now. For change please create pull requests after discussing them at the x86-64-abi@googlegroups.com mailing list (whose archives are at https://groups.google.com/forum/#!forum/x86-64-abi).
If you want to build locally, switch to the x86-64-ABI directory. Then run
% make pdf
which will give you abi.pdf once pdflatex is installed.
Pull requests that are accepted will automatically build a new pdf.
You can find the latest by selecting CI/CD from
the Gitlab/Jobs navigation
bar. Click the download button for the document. You can see the button
highlighted in red in the below image. 
An old testsuite of some ABI traits, very old and incomplete meanwhile, just here for its history.