Debugging the JNI C code would appear to require running java or jdb under gdb and setting break points in the C code. Unfortunately this appears to be particularly tricky. A possible approach is to introduce a sleep(1) in the C code and then use gdb to attach to the java process. Unfortunately even this method does not seem to allow us to set break points.
export LD_LIBRARY_PATH=zxidjava:$LD_LIBRARY_PATH export QUERY_STRING='e=https%3A%2F%2Fidp.symdemo.com%3A8880%2Fidp.xml&l2=+Login+%28SAML20%3APOST%29+&fc=1&fn=prstnt&fq=&fy=&fa=&fm=exact'
N.B. In following "" means Unix shell prompt, "%" gdb prompt, and ">" jdb prompt.
$ gdb jdb % set env LD_LIBRARY_PATH=zxidjava % set env QUERY_STRING=e=https%3A%2F%2Fidp.symdemo.com%3A8880%2Fidp.xml&l2=+Login+%28SAML20%3APOST%29+&fc=1&fn=prstnt&fq=&fy=&fa=&fm=exact % r zxid > stop at zxid:24 > run > next # or step > print cf > cont