[Bug c++/113541] New: Rejects __attribute__((section)) on explicit instantiation declaration of ctor/dtor

[Bug c++/113541] New: Rejects __attribute__((section)) on explicit instantiation declaration of ctor/dtor

[arthur.j.odwyer at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113541

            Bug ID: 113541
           Summary: Rejects __attribute__((section)) on explicit
                    instantiation declaration of ctor/dtor
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arthur.j.odwyer at gmail dot com
  Target Milestone: ---

// https://godbolt.org/z/34Wdj1ox8

template<class T>
struct S {
    S(int) {}
    void operator=(int) {}
    void f(int) {}
    ~S() {}
};
template __attribute__((section("TEST"))) S<int>::S(int); // error
template __attribute__((section("TEST"))) void S<int>::f(int); // OK
template __attribute__((section("TEST"))) void S<int>::operator=(int); // OK
template __attribute__((section("TEST"))) S<int>::~S(); // error

===

<source>: In instantiation of 'S<T>::S(int) [with T = int]':
<source>:9:56:   required from here
<source>:3:5: error: section of alias 'S<T>::S(int) [with T = int]' must match
section of its target
    3 |     S(int) {}
      |     ^

The problem seems to be only with the constructor and destructor, i.e., the two
kinds of functions that codegen two object-code definitions (base object xtor
and complete object xtor) for a single C++ declaration.

Somehow, giving `S` a virtual base class (`struct S : virtual B`) fixes the
problem. Then both codegenned xtors correctly wind up in the "TEST" section.

GCC 4.9.4 is happy with the code as written. The bug started happening with GCC
5.

(This was noted on Slack in June 2019, but never reported on Bugzilla AFAICT
until now: https://cpplang.slack.com/archives/C5GN4SP41/p1560800562026000 )

[Bug c++/113541] Rejects __attribute__((section)) on explicit instantiation declaration of ctor/dtor

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113541

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
                 CC|                            |mpolacek at gcc dot gnu.org
   Last reconfirmed|                            |2024-01-22

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
The error started with r5-1210-ge257a17cb9cc4d.

[Bug c++/113541] Rejects __attribute__((section)) on explicit instantiation declaration of ctor/dtor

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113541

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
            Version|unknown                     |14.0
      Known to work|                            |4.9.4
      Known to fail|                            |5.1.0

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
It sounds like an issue with the C++ mandated aliases.

But I'll note that the template instantiations have to adhere to certain
linkage so I wonder if simply putting them into a different section isn't going
to break the ABI.