From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Berlin To: Jim Blandy Cc: Daniel Berlin , gdb@sources.redhat.com, gdb-patches@sources.redhat.com Subject: Re: RFA: Re: Funky code in gnuv2_virtual_fn_field Date: Wed, 23 May 2001 21:24:00 -0000 Message-id: <87eltfl6iq.fsf@dynamic-addr-83-177.resnet.rochester.edu> References: <20010520160159.3484E5E9DB@zwingli.cygnus.com> <87u22e19kz.fsf@dynamic-addr-83-177.resnet.rochester.edu> X-SW-Source: 2001-05/msg00452.html Jim Blandy writes: > Daniel Berlin writes: > > 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. > > That's what I was afraid of. (I *hate* it when GDB does something > with a `struct value' that isn't really legal, but just happens to be > okay because we know internal details about where that `struct value' > came from...) This is actually why i stopped using value_ptrs when doing the location expression evaluation. Even the value operations and the read_var_value routine seem to "know too much" about struct value, and don't just do what they should. > > > 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. > > Great. So how about this patch? > Approved. > 2001-05-22 Jim Blandy > > * gnu-v2-abi.c (gnuv2_virtual_fn_field): There's no need to clear > VALUE_POINTED_TO_OFFSET here; if value_cast doesn't return a > useful value, then we should fix that instead. > > Index: gdb/gnu-v2-abi.c > =================================================================== > RCS file: /cvs/src/src/gdb/gnu-v2-abi.c,v > retrieving revision 1.2 > diff -c -r1.2 gnu-v2-abi.c > *** gdb/gnu-v2-abi.c 2001/05/12 04:01:16 1.2 > --- gdb/gnu-v2-abi.c 2001/05/22 21:14:35 > *************** > *** 111,117 **** > 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)); > } > --- 111,116 ---- -- ""-Steven Wright