Yeah, this can be done.

Building with -fno-common now works for me on 2.2 and master. Thanks for the patch.

I took your patch but modified it to define EXTERN_UNLESS_MAIN_MODULE only at one place.

It has been fixed in the repo for nearly a year, see T4459. A new release is urgently required and will follow in the next days. I close this as a duplicate.

In a private mail someone else reported a similar problems and explained that gcc-10 will change the default from -fcommon to -fno-common. I think this is again a bad move in compiler development. Replacing the de-facto standard C compiler behaviour with something _allowed_ by ISO-C. No industrial grade toolchain would ever do such a silly default change - too many customers would rightfully be angry with them.

For what I use, please refer: https://tracker.debian.org/pkg/gcc-9

Which one version gcc 9 you've been using?
May I see gcc -v ?

@gniibe already wrote: “With gcc-9 in Debian experimental, everything goes well.”

BTW: fedora corp provides already free access to build envs with gcc 9 which can be easily integrated with CIs.

What you mean " it is not reproducible for u"?
Did you try to use gcc 9 and you had no problems compiling gnupg or you don't have access to build env with gcc 9?
Try to google to "gcc 9 pragma" and you will find several discussions and patches done by people fixing similar issues.

@kloczek , it is not reproducible for us, so, we consider it may be a problem other than GnuPG itself, possibly, some specific build configuration parameter(s) for GCC, or something by unreleased code.
Please file a report with how to reproduce your problem.

Why do you think that it is gcc bug?

So this seems to be a gcc bug, right. Then we should close this bug.