Re: [PATCH] [11/12/13/14 Regression] ABI break in _Hash_node_value_base since GCC 11 [PR 111050]

["François Dumont" <frs.dumont@gmail.com>]

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Author: TC <rs2740@gmail.com>
Date:   Wed Sep 6 19:31:55 2023 +0200

     libstdc++: Force _Hash_node_value_base methods inline to fix abi 
(PR111050)

https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=1b6f0476837205932613ddb2b3429a55c26c409d
     changed _Hash_node_value_base to no longer derive from 
_Hash_node_base, which means
     that its member functions expect _M_storage to be at a different 
offset. So explosions
     result if an out-of-line definition is emitted for any of the 
member functions (say,
     in a non-optimized build) and the resulting object file is then 
linked with code built
     using older version of GCC/libstdc++.

     libstdc++-v3/ChangeLog:

             PR libstdc++/111050
             * include/bits/hashtable_policy.h
             (_Hash_node_value_base<>::_M_valptr(), 
_Hash_node_value_base<>::_M_v())
             Add [[__gnu__::__always_inline__]].

Ok to commit ?

On 12/09/2023 18:09, Jonathan Wakely wrote:
> On Mon, 11 Sept 2023 at 18:19, François Dumont <frs.dumont@gmail.com> wrote:
>>
>> On 11/09/2023 13:51, Jonathan Wakely wrote:
>>> On Sun, 10 Sept 2023 at 14:57, François Dumont via Libstdc++
>>> <libstdc++@gcc.gnu.org> wrote:
>>>> Following confirmation of the fix by TC here is the patch where I'm
>>>> simply adding a 'constexpr' on _M_next().
>>>>
>>>> Please let me know this ChangeLog entry is correct. I would prefer this
>>>> patch to be assigned to 'TC' with me as co-author but I don't know how
>>>> to do such a thing. Unless I need to change my user git identity to do so ?
>>> Sam already explained that, but please check with Tim how he wants to
>>> be credited, if at all. He doesn't have a copyright assignment, and
>>> hasn't added a DCO sign-off to the patch, but it's small enough to not
>>> need it as this is the first contribution credited to him.
>>>
>>>
>>>>        libstdc++: Add constexpr qualification to _Hash_node::_M_next()
>>> What has this constexpr addition got to do with the ABI change and the
>>> always_inline attributes?
>>>
>>> It certainly doesn't seem like it should be the summary line of the
>>> git commit message.
>> Oops, sorry, that's what I had started to do before Tim submitted anything.
>>
>> Here is latest version:
> No patch attached, and the ChangeLog below still mentions the constexpr.
>
> I've pinged Tim via another channel to ask him about the author attribution.
>
>
>> Author: TC <rs2740@gmail.com>
>> Date:   Wed Sep 6 19:31:55 2023 +0200
>>
>>       libstdc++: Force inline on _Hash_node_value_base methods to fix abi
>> (PR111050)
>>
>> https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=1b6f0476837205932613ddb2b3429a55c26c409d
>>       changed _Hash_node_value_base to no longer derive from
>> _Hash_node_base, which means
>>       that its member functions expect _M_storage to be at a different
>> offset. So explosions
>>       result if an out-of-line definition is emitted for any of the
>> member functions (say,
>>       in a non-optimized build) and the resulting object file is then
>> linked with code built
>>       using older version of GCC/libstdc++.
>>
>>       libstdc++-v3/ChangeLog:
>>
>>               PR libstdc++/111050
>>               * include/bits/hashtable_policy.h
>>               (_Hash_node_value_base<>::_M_valptr(),
>> _Hash_node_value_base<>::_M_v())
>>               Add [[__gnu__::__always_inline__]].
>>               (_Hash_node<>::_M_next()): Add constexpr.
>>
>>       Co-authored-by: François Dumont <fdumont@gcc.gnu.org>
>>
>> Ok for you TC (Tim ?) ?
>>
>>

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diff --git a/libstdc++-v3/include/bits/hashtable_policy.h b/libstdc++-v3/include/bits/hashtable_policy.h
index 347d468ea86..86b32fb15f2 100644
--- a/libstdc++-v3/include/bits/hashtable_policy.h
+++ b/libstdc++-v3/include/bits/hashtable_policy.h
@@ -327,18 +327,22 @@ namespace __detail
 
       __gnu_cxx::__aligned_buffer<_Value> _M_storage;
 
+      [[__gnu__::__always_inline__]]
       _Value*
       _M_valptr() noexcept
       { return _M_storage._M_ptr(); }
 
+      [[__gnu__::__always_inline__]]
       const _Value*
       _M_valptr() const noexcept
       { return _M_storage._M_ptr(); }
 
+      [[__gnu__::__always_inline__]]
       _Value&
       _M_v() noexcept
       { return *_M_valptr(); }
 
+      [[__gnu__::__always_inline__]]
       const _Value&
       _M_v() const noexcept
       { return *_M_valptr(); }