VEX currently contains a fossil called "BBPTR", which meant basic block pointer (maybe in some distant past). However through all the VEX, it is used with the meaning of "GSPTR", that is guest state pointer. It is really confusing to read all over the code about BBPTR but in reality GSPTR is meant. The attached patch renames BBPTR to GSPTR and fixes also corresponding comments.
Created attachment 102737 [details] patch for VEX
Created attachment 102738 [details] patch for Valgrind
Fixed in SVN Valgrind r16189, VEX r3287.