Re: [PATCH bpf-next v2 0/5] bpf: tools: support build selftests/bpf with clang

[Yonghong Song <yhs@fb.com>]

On 4/12/21 6:44 PM, Sedat Dilek wrote:
> On Mon, Apr 12, 2021 at 4:29 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, using the above command, 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.
>>
> 
> Might be good to add some hints like when the build stops or errors:
> 
> Like in my case when I had no CONFIG_DEBUG_INFO_BTF set.
> 
> Of course in combination with Clang-LTO a pointer "you need pahole
> version 1.21." and CONFIG_DEBUG_INFO_BTF=y.
> 
> Finally, a hint for missing xxx-dev(el) packages (see Nick's report).
> 
> The tools directory has its own build rules thus I cannot say how to
> check for specific Kconfigs.
> I have not looked.

I will add some more information about how I have tested in the
cover letter.

> 
> NOTE: I have not checked without setting CONFIG_DEBUG_INFO.
> 
> - Sedat -
> 
>> Changelog:
>>    v1 -> v2:
>>      . add -Wno-unused-command-line-argument and -Wno-format-security
>>        for clang only as (1). gcc does not exhibit those
>>        warnings, and (2). -Wno-unused-command-line-argument is
>>        only supported by clang. (Sedat)
>>
>> 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 |  7 ++++++-
>>   tools/testing/selftests/lib.mk       |  4 ++++
>>   4 files changed, 21 insertions(+), 4 deletions(-)
>>
>> --
>> 2.30.2
>>