Unable to set a comment on structures containing a member with a specific function pointer type.

[arizvisa]

In IDA 8.4, a certain combination of types applied to a structure member can result in the removal of comments applied to the members that follow it. After troubleshooting it, the type needs to be a function pointer that returns another function pointer. Something like the following will suffice:

00000000 struct busted // sizeof=0x20
00000000 {
00000000     __int64 field_0;                    // test 1
00000008     __int64 field_8;                    // test 2
00000010     __int64 field_10;                   // test 3
00000018     __int64 field_18;                   // test 4
00000020 };

If you apply the type __int64 (__fastcall ***(__fastcall *field_20)())(_QWORD) to "field_0", notice that the comments are shifted forward. Also notice that you're unable to set a comment on "field_8", since it gets applied to field_10.

00000000 struct busted // sizeof=0x20
00000000 {
00000000     __int64 (__fastcall ***(__fastcall *field_0)())(_QWORD); // test 1
00000008     __int64 field_8;
00000010     __int64 field_10;                   // test 2
00000018     __int64 field_18;                   // test 3
00000020 };

It turns out that the number of comments that get shifted depends on the parameters of the type being applied to "field_0". If you use the type __int64 (__fastcall ***(__fastcall *field_0)())(int, int), which contains two parameters, the next two fields will suffer the described symptom.

00000000 struct busted // sizeof=0x20
00000000 {
00000000     __int64 (__fastcall ***(__fastcall *field_0)())(int, int); // test 1
00000008     __int64 field_8;
00000010     __int64 field_10;
00000018     __int64 field_18;                   // test 2
00000020 };

This bug actually has nothing to do with the plugin and is only logged here for tracking a way to workaround the issue.