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

[Sedat Dilek <sedat.dilek@gmail.com>]

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?

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.

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

- Sedat -