Re: BUG #5590: undefined shift behavior

"John Regehr" <regehr@cs.utah.edu> writes:
> Bug reference:      5590
> Logged by:          John Regehr
> Email address:      regehr@cs.utah.edu
> PostgreSQL version: head 8/2/10
> Operating system:   OSX
> Description:        undefined shift behavior
> Details:

> During a "make check" the left-shift operator at tsquery_util.c 48:18 is
> passed a negative right-hand argument a number of times.

Hmm.  valcrc is declared as signed int32, so depending on what your
compiler thinks the semantics of % is, this clearly can potentially
happen.  I notice the same problem in makeTSQuerySign() in tsquery_op.c.

The fix is presumably to cast the valcrc value to unsigned int before
executing %.  However, I'm a bit worried about whether this could change
the results, and if it did whether that would invalidate any on-disk
data structures.  Oleg, Teodor, do either TSQuerySign or QTNode.sign
ever get to disk?

John: how did you detect this?

            regards, tom lane