from jerror.h:277
#define TRACEMS3(cinfo,lvl,code,p1,p2,p3) \
MAKESTMT(int * _mp = (cinfo)->err->msg_parm.i; \
_mp[0] = (p1); _mp[1] = (p2); _mp[2] = (p3); \
(cinfo)->err->msg_code = (code); \
(*(cinfo)->err->emit_message) ((j_common_ptr) (cinfo), (lvl)); )