* RFA: Re: Funky code in gnuv2_virtual_fn_field [not found] ` <87u22e19kz.fsf@dynamic-addr-83-177.resnet.rochester.edu> @ 2001-05-22 14:16 ` Jim Blandy 2001-05-23 21:24 ` Daniel Berlin 0 siblings, 1 reply; 3+ messages in thread From: Jim Blandy @ 2001-05-22 14:16 UTC (permalink / raw) To: Daniel Berlin; +Cc: gdb, gdb-patches Daniel Berlin <dan@cgsoftware.com> writes: > Jim Blandy <jimb@zwingli.cygnus.com> 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...) > 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? 2001-05-22 Jim Blandy <jimb@redhat.com> * 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 ---- ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: RFA: Re: Funky code in gnuv2_virtual_fn_field 2001-05-22 14:16 ` RFA: Re: Funky code in gnuv2_virtual_fn_field Jim Blandy @ 2001-05-23 21:24 ` Daniel Berlin 2001-05-25 10:10 ` Jim Blandy 0 siblings, 1 reply; 3+ messages in thread From: Daniel Berlin @ 2001-05-23 21:24 UTC (permalink / raw) To: Jim Blandy; +Cc: Daniel Berlin, gdb, gdb-patches Jim Blandy <jimb@zwingli.cygnus.com> writes: > Daniel Berlin <dan@cgsoftware.com> writes: > > Jim Blandy <jimb@zwingli.cygnus.com> 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 <jimb@redhat.com> > > * 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 ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: RFA: Re: Funky code in gnuv2_virtual_fn_field 2001-05-23 21:24 ` Daniel Berlin @ 2001-05-25 10:10 ` Jim Blandy 0 siblings, 0 replies; 3+ messages in thread From: Jim Blandy @ 2001-05-25 10:10 UTC (permalink / raw) To: Daniel Berlin; +Cc: gdb, gdb-patches Daniel Berlin <dan@cgsoftware.com> writes: > Jim Blandy <jimb@zwingli.cygnus.com> writes: > > Great. So how about this patch? > > Approved. Committed. > > 2001-05-22 Jim Blandy <jimb@redhat.com> > > > > * 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. ^ permalink raw reply [flat|nested] 3+ messages in thread
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2001-05-22 14:16 ` RFA: Re: Funky code in gnuv2_virtual_fn_field Jim Blandy
2001-05-23 21:24 ` Daniel Berlin
2001-05-25 10:10 ` Jim Blandy
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