c++: -fsanitize=vptr and -fstrong-eval-order. [PR95221]
With -fstrong-eval-order=all we evaluate the function address before the
arguments. But this caused trouble with virtual functions and
-fsanitize=vptr; we would do vptr sanitization as part of calculating the
'this' argument, and separately look at the vptr in order to find the
function address. Without -fstrong-eval-order=all 'this' is evaluated
first, but with that flag the function address is evaluated first, so we
would access the null vptr before sanitizing it.
Fixed by instrumenting the OBJ_TYPE_REF of a virtual function call instead
of the 'this' argument.
This issue suggests that we should be running the ubsan tests in multiple
standard modes like the rest of the G++ testsuite, so I've made that change
as well.
gcc/cp/ChangeLog:
* cp-ubsan.c (cp_ubsan_maybe_instrument_member_call): For a virtual
call, instrument the OBJ_TYPE_REF.