arm allmodconfig build issue with bpf

[John Garry]

Hi all,

For some time, the arm allmodconfig build has had this following build 
issue for me:

$ make net/bpf/test_run.o
   CALL    scripts/checksyscalls.sh
   CC      net/bpf/test_run.o
net/bpf/test_run.c:522:1: error: ‘retain’ attribute ignored 
[-Werror=attributes]
   522 | {
       | ^
net/bpf/test_run.c:568:1: error: ‘retain’ attribute ignored 
[-Werror=attributes]
   568 | {
       | ^
net/bpf/test_run.c:577:1: error: ‘retain’ attribute ignored 
[-Werror=attributes]
   577 | {
       | ^
net/bpf/test_run.c:584:1: error: ‘retain’ attribute ignored 
[-Werror=attributes]
   584 | {
       | ^
net/bpf/test_run.c:590:1: error: ‘retain’ attribute ignored 
[-Werror=attributes]
   590 | {
       | ^
net/bpf/test_run.c:619:1: error: ‘retain’ attribute ignored 
[-Werror=attributes]
   619 | {
       | ^
net/bpf/test_run.c:624:1: error: ‘retain’ attribute ignored 
[-Werror=attributes]
   624 | {
       | ^
net/bpf/test_run.c:630:1: error: ‘retain’ attribute ignored 
[-Werror=attributes]
   630 | {
       | ^
net/bpf/test_run.c:634:1: error: ‘retain’ attribute ignored 
[-Werror=attributes]
   634 | {
       | ^
cc1: all warnings being treated as errors
make[4]: *** [scripts/Makefile.build:194: net/bpf/test_run.o] Error 1
make[3]: *** [scripts/Makefile.build:440: net/bpf] Error 2
make[2]: *** [scripts/Makefile.build:440: net] Error 2
make[1]: *** [/home/ubuntu/mnt/linux2/Makefile:1989: .] Error 2
make: *** [Makefile:251: __sub-make] Error 2
ubuntu at jgarry-ubuntu-bm5-instance-20230215-1843:~/mnt/linux2$

The issue comes the definition of __bpf_kfunc from include/linux/btf.h

Other files which include btf.h, like kernel/cgroup/rstat.c, have this 
same issue.

I am crossing compiling with the following:

$ /usr/bin/arm-linux-gnueabihf-gcc --version
arm-linux-gnueabihf-gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Normally I bodge a fix like:

---->8----

diff --git a/include/linux/btf.h b/include/linux/btf.h
index b12c63af9e78..4214e76c9168 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -83,7 +83,7 @@
   * as to avoid issues such as the compiler inlining or eliding either 
a static
   * kfunc, or a global kfunc in an LTO build.
   */
-#define __bpf_kfunc
+#define __bpf_kfunc __used __retain noinline

  #define __bpf_kfunc_start_defs() 
        \
         __diag_push();


----8<----

Any proposals to properly fix this?

Thanks,
John