Tcl Source Code

Part of the sequence of events leading to the segfault
is the 

SAVE_CONTEXT(corPtr->caller);

around line 8740 or so in tclBasic.c (in the TIP 396 commit,
in case the file has changed a lot since then).

This is called at a time when iPtr->cmdFramePtr is NULL,
which puts the NULL value in place which [info frame] later
crashes on attempting to dereference.