Re: [PATCH bpf-next 0/5] support build selftests/bpf with clang

[Yonghong Song <yhs@fb.com>]

On 4/10/21 12:19 PM, Sedat Dilek wrote:
> On Sat, Apr 10, 2021 at 6:49 PM Yonghong Song <yhs@fb.com> wrote:
>>
>> To build kernel with clang, people typically use
>>    make -j60 LLVM=1 LLVM_IAS=1
>> LLVM_IAS=1 is not required for non-LTO build but
>> is required for LTO build. In my environment,
>> I am always having LLVM_IAS=1 regardless of
>> whether LTO is enabled or not.
>>
>> After kernel is build with clang, the following command
>> can be used to build selftests with clang:
>>    make -j60 -C tools/testing/selftests/bpf LLVM=1 LLVM_IAS=1
>>
>> But currently, some compilations still use gcc
>> and there are also compilation errors and warnings.
>> This patch set intends to fix these issues.
>> Patch #1 and #2 fixed the issue so clang/clang++ is
>> used instead of gcc/g++. Patch #3 fixed a compilation
>> failure. Patch #4 and #5 fixed various compiler warnings.
>>
>> Yonghong Song (5):
>>    selftests: set CC to clang in lib.mk if LLVM is set
>>    tools: allow proper CC/CXX/... override with LLVM=1 in
>>      Makefile.include
>>    selftests/bpf: fix test_cpp compilation failure with clang
>>    selftests/bpf: silence clang compilation warnings
>>    bpftool: fix a clang compilation warning
>>
>>   tools/bpf/bpftool/net.c              |  2 +-
>>   tools/scripts/Makefile.include       | 12 ++++++++++--
>>   tools/testing/selftests/bpf/Makefile |  4 +++-
>>   tools/testing/selftests/lib.mk       |  4 ++++
>>   4 files changed, 18 insertions(+), 4 deletions(-)
>>
>> --
>> 2.30.2
>>
> 
> Thanks for CCing me and taking care to clean BPF selftests with clang.
> 
> I applied (adapted 4/5) the 5 patches to fit latest Linus Git.
> 
> As I had a fresh compiled Clang-CFI kernel without enabling BTF
> debug-info KConfig this fails at some point.
> I am not sure what the situation is with Clang-CFI + BTF thus I will
> do another Clang-LTO build with BTF enabled.
> So, I was not able to build test_cpp.
> 
> I am missing some comments that LLVM=1 misses to set CXX=clang++ if
> people want that explicitly as CXX.
> Did you try with this?

Yes, this patch set should fix this issue.

> 
> AFAICS LC_ALL=C was not the culprit.
> Did you try with and without LC_ALL=C - I have this in all my build-scripts.
> Here I have German localisation as default.

Just tried. Yes, LC_ALL=C does not impact compilation any more
with this patch set.

> 
> Wil report later... (might be Monday when Linux v5.12-rc7 is released).
> 
> - Sedat -
>