This patch fixes a loophole in the -fstack-protector-strong protection. 
  If a function call uses the return slot optimization, the caller needs 
stack protector instrumentation because the return slot is addressable.

Bootstrapped and regression-tested on x86_64-redhat-linux-gnu, with 
C/C++/Java enabled.  Okay for trunk?

-- 
Florian Weimer / Red Hat Product Security Team