I have a shared NTFS drive between Linux and Windows. In Linux I mount the NTFS drive with the 'exec' option (as default) so I can compile and run binaries. However 'exec' makes all files within the drive executable.

When I try to colocate a git repo on this drive, jj reports every file as being modified to be executable. While they all are executable, I don't want this represented as a change in the repo. Running jj chmod normal <some_file> does nothing because the drive is mounted with all files executable, and jj continues to report everything as modified to be executable.

Git has an option for this as core.fileMode.

Here is git's documentation:
https://git-scm.com/docs/git-config#Documentation/git-config.txt-corefileMode

core.fileMode

Tells Git if the executable bit of files in the working tree is to be honored.

Some filesystems lose the executable bit when a file that is marked as executable is checked out, or checks out a non-executable file with executable bit on. git-clone[1] or git-init[1] probe the filesystem to see if it handles the executable bit correctly and this variable is automatically set as necessary.

A repository, however, may be on a filesystem that handles the filemode correctly, and this variable is set to true when created, but later may be made accessible from another environment that loses the filemode (e.g. exporting ext4 via CIFS mount, visiting a Cygwin created repository with Git for Windows or Eclipse). In such a case it may be necessary to set this variable to false. See git-update-index[1].

The default is true (when core.filemode is not specified in the config file).

I'm not sure how an option like this might integrate with JJ's use of executable bits in windows, but it would be nice to add some solution for filesystems on Linux that can't easily control the executable bit.