Created attachment 4309 Change size of acToolTips from 256 to BUFMAX. If a program outputs a tooltip longer than 256 bytes, a buffer in DisplayCmdOutput of main.c is overflowed leading to a segmentation fault. In DisplayCmdOutput in main.c, acToolTips is a 256-byte char array to hold the tooltip provided by the external program. However, the program may provide as much as 1024 bytes of XML output (since struct genmon_t::acValue is a 1024-byte char array, a size which is passed to genmon_SpawnCmd), and the smaller buffer size isn't honored when the tooltip is extracted in DisplayCmdOutput. Attached patch that simply changes the size of acToolTips from 256 to BUFMAX (same size used by genmon_t).
Fixed even better by not using fixed-length buffers at all: http://git.xfce.org/panel-plugins/xfce4-genmon-plugin/commit/?id=1658dc71ea866fd28fa4c617cadc763260765b33