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

[Konstantin Khorenko <khorenko@virtuozzo.com>]

ping
1. task for sending this patch to mainstream, link to the https://virtuozzo.atlassian.net/browse/VSTOR-127585
2. sending the patch to ms

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

On 8/27/26 16:29, Eva Kurchatova (Virtuozzo) wrote:
> 
> On 8/27/26 15:42, Konstantin Khorenko wrote:
>> On 8/26/26 22:08, Eva Kurchatova (Virtuozzo) wrote:
>>> 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@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.
>> Not sure i understand this correctly: if we take ms kernel and compile selftests, will those warnings appear?
>> If yes - then mainstream will be happy to apply the fix(es).
>>
>> If not, please explain what is the difference between ms vs rh - both here and in the jira bug.
> 
> Yes, these warnings will appear, but the current fix only suffices for 
> an x86_64 host, where `__seg_gs`, etc attributes are used within the 
> arch-specific kernel headers. If this kselftest was built on, say arm64, 
> different warnings would likely surface which were out of scope. In 
> general this patch is more of a workaround than the solution to the 
> original problem: Arch-specific headers are used while compiling into 
> BPF bytecode. That is why I originally only envisioned it as a fix for 
> compile failures in Virtiozzo CI. Around the time of the submission of 
> this patch, I tried to work on a more advanced solution, that would use 
> arch-generic headers to build BPF programs. But soon that proved 
> unsuccessful given that arch-specific headers directly alter the kernel 
> structure and memory layout, which the BPF programs must understand.
> 
> 
>>> 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.
>> i will review that series.
> 
> 
> I will improve this patch description, and send it within batch of other 
> BPF fixes you are currently reviewing when they are ready. Thanks.
> 

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