Upcoming metadata changes

[cjihrig]

The following changes are coming:

• v8dbg_class_Map__inobject_properties_or_constructor_function_index__int
  • This is now v8dbg_class_Map__inobject_properties_start_or_constructor_function_index__char as of v8/v8@61bf2cc
• v8dbg_class_Map__instance_attributes__int
  • This is now v8dbg_class_Map__instance_type__uint16_t as of v8/v8@c00bb6d and v8/v8@cb46310
• v8dbg_class_Map__instance_size__int
  • This is now v8dbg_class_Map__instance_size_in_words__char as of v8/v8@61bf2cc
• v8dbg_bit_field3_dictionary_map_shift
  • This is now v8dbg_bit_field3_is_dictionary_map_shift as of v8/v8@7a159da

See nodejs/node-v8#34

[mmarchini]

These metadata changes landed with nodejs/node#17489, thus llnode is not working with node compiled from source. There's also one more missing: v8dbg_prop_type_mask.

[cjihrig]

There's also one more missing: v8dbg_prop_type_mask.

That one is expected. It's used here for Node.js version detection.

[mmarchini]

I think we should reopen this Issue, we updated the metadata names, but we didn't fix semantic changes. npm test have six failing tests on Node.js v10.0.0.

I started to investigate them, and I think at least three failures are happening because of v8/v8@61bf2cc. If I understood the patch correctly, it moved the internal properties of Map, confusing llnode once it tries to inspect objects. For example, in our inspect-test, Class.x should be 1 and Class.hashmap should be an object, but instead, they both are pointing to the internal Map:

(lldb) v8 findjsinstances -d Class
0x000030c00446cd11:<Object: Class properties {
    .x=0x000030c077382341:<Map own_descriptors=0 in_object=0 instance_size=8 descriptors=0x000030c0b6e02231>,
    .y=0.000000,
    .hashmap=0x000030c077382341:<Map own_descriptors=0 in_object=0 instance_size=8 descriptors=0x000030c0b6e02231>}
  internal fields {
    0x0000000100000000,
      0x405edd2f1a9fbe77,
      0x000030c00446ce09,
      0x000030c077382341,
      0x000030c077382341,
      0x000030c077382341,
      0x000030c077382341,
      0x000030c077382341}>

FWIW all failures from npm test can be reproduced with v10.0.0-v8-canary20171123e31a70aef2 from https://nodejs.org/download/v8-canary/, which means changes made on v8/v8@7a159da should already be fixed in llnode 😄