On Wed, Nov 26, 2014 at 11:18:11AM -0500, Jason Merrill wrote: > On 10/28/2014 08:44 AM, Jakub Jelinek wrote: > >+cp_ubsan_check_member_access_r (tree *stmt_p, int *walk_subtrees, void > >*data) > > This function needs a longer comment about exactly what forms it's trying to > instrument.
Ok, will do. > >+ /* T t; t.foo (); doesn't need instrumentation, if the type is known. */ > >+ if (is_addr > >+ && TREE_CODE (op) == ADDR_EXPR > >+ && DECL_P (TREE_OPERAND (op, 0)) > >+ && same_type_p (type, > >+ TYPE_MAIN_VARIANT (TREE_TYPE (TREE_OPERAND (op, 0))))) > >+ return NULL_TREE; > > How do we know the decl's vptr hasn't been clobbered? This seems like one > of the optimizations we decided to drop. Yeah, will try to remove this hunk and see what it changes. > >+ if (TREE_CODE (base) == COMPONENT_REF > >+ && DECL_ARTIFICIAL (TREE_OPERAND (base, 1))) > >+ { > >+ tree base2 = TREE_OPERAND (base, 0); > >+ while (TREE_CODE (base2) == COMPONENT_REF > >+ || TREE_CODE (base2) == ARRAY_REF > >+ || TREE_CODE (base2) == ARRAY_RANGE_REF) > >+ base2 = TREE_OPERAND (base2, 0); > >+ if (TREE_CODE (base2) != INDIRECT_REF > >+ && TREE_CODE (base2) != MEM_REF) > >+ return; > >+ } > >+ else if (TREE_CODE (base) != INDIRECT_REF > >+ && TREE_CODE (base) != MEM_REF) > >+ return; > > Why do you look through ARRAY_REF here? An element of an array is its own > complete object. That had to do with only instrumenting dereferences surrounded by handled components, but not accesses to decls (so p->x gets instrumented but q.x for VAR_DECL q is not). If we want to instrument that, then I'll need to tweak the member access instrumentation some more. Today I found that the C++14 constexpr changes unfortunately mean I have to make bigger changes, so I'm rewriting it to use UBSAN_VPTR internal calls and only lower that during sanopt (and will try to optimize clearly unnecessary checks at that point to offset from the FE instrumenting more - if the optimizers can prove virtual table of the object has not been changed since dominating UBSAN_VPTR, we don't need to instrument it again. Jakub