[Devel] [PATCH vz10 5/5] fixup! samples/bpf: fix -Wduplicate-decl-specifier and -Wmissing-declarations

[Eva Kurchatova (Virtuozzo)]

On 8/18/26 20:00, Konstantin Khorenko wrote:
> i have asked to send this patch to mainstream first.
>
> Please, add a link to the mainstream version of the patch to https://virtuozzo.atlassian.net/browse/VSTOR-127585
>
> --
> Best regards,
>
> Konstantin Khorenko,
> Virtuozzo Linux Kernel Team
>
> On 6/25/26 20:16, Eva Kurchatova wrote:
>> BPF programs include arch-specific headers, which use address space
>> qualifiers for percpu variables via __seg_gs / __seg_fs, however those
>> are meaningless for BPF compiler and will raise a warning
>>
>> Fix this by redefining __seg_gs and __seg_fs to a no-op attribute
>>
>> Additionally, enable ms-extensions, as generated vmlinux.h uses these
>> for structure layout inheritance, an acceptable practice in upstream
>>
>> https://virtuozzo.atlassian.net/browse/VSTOR-127585
>> Feature: fix selftests
>>
>> Signed-off-by: Eva Kurchatova <eva.kurchatova at virtuozzo.com>
>> ---
>>   samples/bpf/Makefile | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
>> index 2b93779b9cbf..39b20bb69bcd 100644
>> --- a/samples/bpf/Makefile
>> +++ b/samples/bpf/Makefile
>> @@ -339,9 +339,11 @@ CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
>>   
>>   $(obj)/xdp_router_ipv4.bpf.o: $(obj)/xdp_sample.bpf.o
>>   
>> +# Generated vmlinux.h uses ms-extensions to inherit struct layout
>>   $(obj)/%.bpf.o: $(src)/%.bpf.c $(obj)/vmlinux.h $(src)/xdp_sample.bpf.h $(src)/xdp_sample_shared.h
>>   	@echo "  CLANG-BPF " $@
>>   	$(Q)$(CLANG) -g -O2 --target=bpf -D__TARGET_ARCH_$(SRCARCH) \
>> +		-fms-extensions -Wno-microsoft-anon-tag \
>>   		-Wno-compare-distinct-pointer-types -I$(srctree)/include \
>>   		-I$(srctree)/samples/bpf -I$(srctree)/tools/include \
>>   		-I$(LIBBPF_INCLUDE) $(CLANG_SYS_INCLUDES) \
>> @@ -372,11 +374,13 @@ $(BPF_SKELS_LINKED): $(BPF_OBJS_LINKED) $(BPFTOOL)
>>   # with native target, e.g., x64, arm64, etc. 'opt' does bpf CORE IR builtin
>>   # processing (llvm12) and IR optimizations. 'llvm-dis' converts
>>   # 'opt' output to IR, and finally 'llc' generates bpf byte code.
>> +# Additionally, __seg_gs and __seg_fs are ignored in BPF code
>>   $(obj)/%.o: $(src)/%.c
>>   	@echo "  CLANG-bpf " $@
>>   	$(Q)$(CLANG) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(BPF_EXTRA_CFLAGS) \
>>   		-I$(obj) -I$(srctree)/tools/testing/selftests/bpf/ \
>>   		-I$(LIBBPF_INCLUDE) $(CLANG_SYS_INCLUDES) \
>> +		-U__seg_gs -D__seg_gs= -U__seg_fs -D__seg_fs= \
>>   		-D__KERNEL__ -D__BPF_TRACING__ -Wno-unused-value -Wno-pointer-sign \
>>   		-D__TARGET_ARCH_$(SRCARCH) -Wno-compare-distinct-pointer-types \
>>   		-Wno-gnu-variable-sized-type-not-at-end \

This patch was made at a point when RHEL hardening flags leaked into 
kselftests build, and at `-Wall -Wextra -Werror`, many build failures 
surfaced.

Today the build does not fail: the spec undefines _fortify_level and 
_hardened_build for this package, so a full samples/bpf build exits 0 
with 166 warnings and no errors, all 13 .bpf.o and 38 sample binaries 
produced. Of those warnings, 104 are exactly the ones this patch removes.

Does it still make sense to keep it, send upstream and backport back, or 
should this patch be dropped? I am not sure upstream will accept this 
patch as it stands, it was originally purely solving VZ-specific CI 
failures.

Please also review the 4-commit patch series from Aug 21, non-backported 
commits starting from "[PATCH vz10 2/4] selftests/bpf: run the network 
tests in their own netns" first, so I can send a batch to upstream.