[Bug c++/123957] New: Using `extern "C"` directive inside anonymous namespace results in mangled name

[mike at sillyhouse dot net via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123957

            Bug ID: 123957
           Summary: Using `extern "C"` directive inside anonymous
                    namespace results in mangled name
           Product: gcc
           Version: 15.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mike at sillyhouse dot net
  Target Milestone: ---

The following minimal example fails to compile with GCC 15.2.1.
Using Fedora 43 but verified behaviour at at https://gcc.godbolt.org/.
Bug present in GCC 15.1 and 15.2.

Error given is: undefined reference to `(anonymous namespace)::testval'.

Expect `testval` symbol to be generated, but instead we get
`_ZN12_GLOBAL__N_17testvalE`.


        #include <stdio.h>

        namespace
        {
        __asm__(".type testval, @object\n"
                        "testval:\n"
                        ".long 0x2badf00d\n");

        extern "C" const unsigned testval; ///<< Problem line

        } // namespace

        int main()
        {
                printf("testval = 0x%08x\n", testval);
                return 0;
        }