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From: "maennich at android dot com" <sourceware-bugzilla@sourceware.org>
To: libabigail@sourceware.org
Subject: [Bug default/27715] Fails to detect GObjectClass ABI changes
Date: Wed, 14 Apr 2021 10:53:45 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D27715

--- Comment #9 from Matthias Maennich <maennich at android dot com> ---
Anything passed to the API via opaque pointers is essentially hidden from A=
BI
analysis as no type information (other than void*) is attached to it. From =
an
ABI point of view the ABI of the symbol that passes void* is unchanged. Tho=
ugh
further down this of course can become incompatible.

There are cases that you intentionally want to pass void* to be ABI compati=
ble
even though the type changes. E.g. if your library has such an interface:

void* get_handle(){
  // allocates the resources and returns just a handle to it.
  ...
  return (void*) some_object;
}

void do_something(void* handle) {
  // uses the handle as a reference
}

The ABI is stable even though the type could have changed. The client code
might not even know the concrete type and is also not supposed to cast to i=
t.

So, as much as I would also like to sometimes inspect underlying types of
void*, flagging changes to those types is probably wrong. If you want this =
type
to be stable, you need to let it participate as a type in the interface.

One way of achieving this is to define a symbol just for the sake of ABI
analysis:

void (struct _GTypeModuleClass obj) { }

This will get picked up by libabigail and the type will participate in the
analysis then.

--=20
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