On 02/18/2016 01:24 AM, Markus Armbruster wrote:
>> For simple unions, you could have (well, still can have, until my later
>> patch gets rid of the simple_union_type() magic):
>>
>> struct SU {
>> SUKind type;
>> union {
>> void *data;
>> int8_t byte;
>> } u;
>> };
>
> Begs the question why that works :)By sheer luck, and (poorly?) documented in a hairy comment in qapi-dealloc-visitor.c (at least, until I delete visit_start_union). We have a data-dependent decision (not only the contents of 'byte', but ALSO the contents of the padding bits), but either the decision results in calling visit_type_int8() (and doing nothing) or skipping the call (and likewise doing nothing). >> I guess I may try and reword this slightly, and point to the fact that >> the NULL dereference was due to calling visit_start_implicit_FOO() (only >> done for flat unions; for simple unions the branches call >> visit_type_FOO(), and that call safely handled NULL); > > That's why it works? > >> But now that visit_type_implicit_FOO() is gone, my earlier incantation >> got reduced in size. I guess it's all in how I document the commit message. > > Give it a try :) I gave it my best in v11 :) Maybe you'll still have wording improvements, but this back-and-forth has helped both of us try to actually characterize what is going on. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
signature.asc
Description: OpenPGP digital signature
