The kernel is now built with -fms-extensions. Anonymous structs or unions permitted by these extensions have been used in several places, and can end up in the generated vmlinux.h file, for example: struct ns_tree { [...] }; [...] struct ns_common { [...] union { struct ns_tree; struct callback_head ns_rcu; }; }; Trying to include this header for compiling a tool may result in build warnings, if the compiler does not expect these extensions. This is the case, for example, with bpftool: In file included from skeleton/pid_iter.bpf.c:3: .../tools/testing/selftests/bpf/tools/build/bpftool/vmlinux.h:64057:3: warning: declaration does not declare anything [-Wmissing-declarations] 64057 | struct ns_tree; | ^~~~~~~~~~~~~~ Fix these build warnings in bpftool by turning on Microsoft extensions when compiling the two BPF programs that rely on vmlinux.h. Reported-by: Alexei Starovoitov Closes: https://lore.kernel.org/bpf/CAADnVQK9ZkPC7+R5VXKHVdtj8tumpMXm7BTp0u9CoiFLz_aPTg@mail.gmail.com/ Signed-off-by: Quentin Monnet --- tools/bpf/bpftool/Makefile | 2 ++ 1 file changed, 2 insertions(+) diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile index 586d1b2595d1..5442073a2e42 100644 --- a/tools/bpf/bpftool/Makefile +++ b/tools/bpf/bpftool/Makefile @@ -224,6 +224,8 @@ endif $(OUTPUT)%.bpf.o: skeleton/%.bpf.c $(OUTPUT)vmlinux.h $(LIBBPF_BOOTSTRAP) $(QUIET_CLANG)$(CLANG) \ + -Wno-microsoft-anon-tag \ + -fms-extensions \ -I$(or $(OUTPUT),.) \ -I$(srctree)/tools/include/uapi/ \ -I$(LIBBPF_BOOTSTRAP_INCLUDE) \ -- 2.43.0