[Bug c/110947] New: Should -Wmissing-variable-declarations not trigger on register variables?

[ndesaulniers at google dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110947

            Bug ID: 110947
           Summary: Should -Wmissing-variable-declarations not trigger on
                    register variables?
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ndesaulniers at google dot com
  Target Milestone: ---

Via:
https://lore.kernel.org/all/CAKwvOd=8kxkD9p+WW-F047ShN=r32slyyfpgzhydw3bxtdd...@mail.gmail.com/

I'm looking to enable -Wmissing-variable-declarations in the Linux kernel
(gcc-14 just gained support for this warning).

In one case I noticed that:

register unsigned long current_stack_pointer asm("rsp");

declared in a header would trigger this:

> no previous declaration for 'current_stack_pointer' 
> [-Wmissing-variable-declarations]

So we could add:

extern unsigned long current_stack_pointer;

before the

register unsigned long current_stack_pointer asm("rsp");

but that seems excessive. Perhaps we can simply not diagnose in that case?

Filed this bug report against clang as well:
https://github.com/llvm/llvm-project/issues/64509