Handling argc==0 in the kernel

But if any setuid program actually relies on argv[0] being the name of the program, that's a severe bug (symlinks, TOCTOU, etc., never mind the fact that the caller can always specify any string they want.)

If the kernel were to silently replace argc==0 with argc==1, it seems like using an empty string would be most parsimonious. At least an empty string is guaranteed not to be a valid filename, whereas /proc/self/exe or the name of the executable might or might not be.