[Bug c/114818] New: 'constructor', 'destructor' function attributes vs. 'extern'

[Bug c/114818] New: 'constructor', 'destructor' function attributes vs. 'extern'

[tschwinge at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114818

            Bug ID: 114818
           Summary: 'constructor', 'destructor' function attributes vs.
                    'extern'
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: diagnostic, documentation
          Severity: minor
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tschwinge at gcc dot gnu.org
  Target Milestone: ---

By chance, I noticed that when 'constructor', 'destructor' function attributes
appear on an 'extern' function declaration, then that is (a) accepted without
any diagnostic by the C, C++ front ends, but (b) no 'constructor', 'destructor'
calls are emitted.  (Doesn't matter whether the function does or doesn't get
linked in.)

Assuming that is the expected behavior, should we update 'gcc/doc/extend.texi'
for this, and implement a diagnostic (warning or even error, enabled by
default)?

I found that in 'gcc/doc/tm.texi', '@node Initialization' we state:

    [...] Each
    object file that defines an initialization function also puts a word in
    the constructor section to point to that function.  [...]

Note "defines", which excludes 'extern'.