Hmm, am still confused. Will pick your brain when I'm in MUC next week :)

On Thu, Oct 13, 2016 at 6:11 AM, Hannes Payer <hpa...@chromium.org> wrote:

> This one you need because it verifies the content of the object fields,
> i.e. the invariants.
>
> On Wed, Oct 12, 2016 at 7:01 PM Adam Klein <ad...@chromium.org> wrote:
>
>> Thanks, Hannes. Are the calls to VerifyPointer() in AccessorPairVerify
>> also redundant?
>>
>> On Wed, Oct 12, 2016 at 12:50 AM, 'Hannes Payer' via v8-dev <
>> v8-dev@googlegroups.com> wrote:
>>
>> Interesting observation.
>>
>> The recursion in Box with ObjectVerify seems indeed redundant since the
>> referenced object will be found by the verifier later.
>> It should be fine if we just verify basic invariants in object-debug.cc,
>> given that there is an iterator that feeds the verifier with objects (which
>> is the case for the heap verifier).
>>
>> On Wed, Oct 12, 2016 at 1:41 AM Adam Klein <ad...@chromium.org> wrote:
>>
>> +some GC folks directly
>>
>> On Tue, Oct 4, 2016 at 11:51 AM, Adam Klein <ad...@chromium.org> wrote:
>>
>> It seems there's some confusion (likely on my part) about what code needs
>> to be added to objects-debug.cc when adding a new HeapObject. Consider two
>> different Structs, AccessorPair and Box:
>>
>> void AccessorPair::AccessorPairVerify() {
>>   CHECK(IsAccessorPair());
>>   VerifyPointer(getter());
>>   VerifyPointer(setter());
>> }
>>
>> void Box::BoxVerify() {
>>   CHECK(IsBox());
>>   value()->ObjectVerify();
>> }
>>
>> AccessorPair only calls VerifyPointer, which checks that the fields is
>> either a Smi or is a pointer to a HeapObject that lives in the Heap.
>> Meanwhile Box recurses into ObjectVerify on the thing it wraps. Which is
>> correct?
>>
>> Reading Heap::Verify, it seems we call Verify on each space, which calls
>> ObjectVerify() followed by iterating the body with a VerifyPointersVisitor.
>> Which looks like it does something very similar to VerifyPointer(). So the
>> call to VerifyPointer() in AccessorPairVerify looks redundant.
>>
>> What about the call to ObjectVerify() in BoxVerify? I expect we'll end up
>> eventually calling ObjectVerify whenever the heap iteration hits
>> Box::value() (and as per the previous paragraph, assuming we've already
>> verified that the pointer is _in_ the heap).
>>
>> So do we really need anything in object-debug.cc other than specific
>> invariants about the contents? Say, a field that ought to be one of a few
>> object types.
>>
>> - Adam
>>
>>
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