I doubt that this is a full solution to the described problem because under Windows "/" is not the root of all files.

Thinking again about this: The easiest way is to move the existing chdir ("/") out of the ifndef W32 block. That is moving just the #endif.

Or we move to the user's home directory - but that is more work.

Andre: What do you think?

Homedir is an obvious choice, but I don't think make_absfilename adds a drive letter. Another idea is to use GetWindowsDirectory() or GetSystemDirectory. Note that chdir is deprecated by MSFT, hence _chdir.

Indeed _chdir("/"); might still be problematic. Because as werner says it would create problems e.g. if you sign a file on a network drive or removable device because the agents homedir would then be the root of the device.

E.g.
e:
chdir \

would keep you on E:\ and lock a removable device.

I think the default would be %HOMEDRIVE%%HOMEPATH% (users homedir) this is what windows sets as execution dir for pinned shortcuts and thats for example the working directory of Kleopatra.

I would avoid that though because we would then need to handle Unicode User names and SetCurrentDirectoryW etc. and don't need a writable working directory.

Maybe something like:

if (_chdir (getenv("HOMEDRIVE")) && _chdir ("/"))
  {
     log_error ("chdir to / failed: %s\n", strerror (errno));
     exit (1);
  }

Untested.