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From: "john at drouhard dot dev" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/111050] [11/12/13/14 Regression] ABI break in
 _Hash_node_value_base since GCC 11
Date: Tue, 12 Sep 2023 15:54:37 +0000
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X-Bugzilla-Keywords: ABI
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111050

John Drouhard <john at drouhard dot dev> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |john at drouhard dot dev

--- Comment #10 from John Drouhard <john at drouhard dot dev> ---
(In reply to frs.dumont from comment #9)
> To be honest before that report I thought that preserving abi was just a=
=20
> matter of preserving memory layout of types. I had no idea that member=20
> methods mattered !

(I was the original reporter of this to TC)

I think the specific issue here is that the member function `_M_valptr()`
returns the address of the storage data member, and that _function_ is used=
 in
a construct call elsewhere to point to the address where a new object shoul=
d be
placed. It returns the address based on the offset from the beginning of the
object which changed when the base class (which had its own data members) w=
as
removed.

So, if the function isn't inlined, the symbol that's actually loaded by the
dynamic linker during runtime will return a potentially bogus address for t=
hat
data member if the definition of that function came from a library compiled
with the other version.=