From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Berlin To: Jim Blandy Cc: Daniel Berlin , gdb@sources.redhat.com Subject: Re: Funky code in gnuv2_virtual_fn_field Date: Mon, 21 May 2001 18:01:00 -0000 Message-id: <87u22e19kz.fsf@dynamic-addr-83-177.resnet.rochester.edu> References: <20010520160159.3484E5E9DB@zwingli.cygnus.com> X-SW-Source: 2001-05/msg00310.html Jim Blandy writes: > I'm looking at lines 112--118 in gnu-v2-abi.c: > > if (TYPE_TARGET_TYPE (context) != type1) > { > value_ptr tmp = value_cast (context, value_addr (arg1)); > VALUE_POINTED_TO_OFFSET (tmp) = 0; > arg1 = value_ind (tmp); > type1 = check_typedef (VALUE_TYPE (arg1)); > } > > This looks fishy to me. If we smash the POINTED_TO_OFFSET without > smashing the ENCLOSING_TYPE in a corresponding manner, and then we > indirect through that pointer, don't we get a value whose > ENCLOSING_TYPE is set, but whose address points to the embedded > object, and not the enclosing object? Yup. However, although it's not documented anywhere, value_cast approriately smashes the enclosing type. In fact, it should also smash the pointed_to_offset when necessary, making this explicit smashing pointless, and possibly incorrect. Though now that i look at it some more, I'm not positive value_cast is doing the right thing in all cases. It's pretty hard to follow, however, and I just got home from a 7 hour car ride (graduated yesterday, and moved out), so i may just be loopy. IMHO, in any case, we shouldn't be needing to set the pointed_to_offset here. If we have to, value_cast is doing something wrong, or not enough of the right thing. This is because all we are trying to do is a simple cast, which is what value_cast is supposed to do for us. If we have to start mucking around with it's results to get a correct value, then it's not doing it's job right, or completely. -- "I hooked up my accelerator pedal in my car to my brake lights. I hit the gas, people behind me stop, and I'm gone. "-Steven Wright