Re: [PATCH v2 1/4] selftests: add shared lib.bpf.mk to build BPF progs and skeletons

[Viktor Malik <vmalik@redhat.com>]

On 8/6/26 21:48, Ziyang Men wrote:
> On Wed, Jul 22, 2026 at 08:50:06AM +0200, Viktor Malik wrote:

[...]

> Hi Viktor, 
> 
> Thanks for your suggestions!
>>
>> Looking at the same line in tools/testing/selftests/bpf/Makefile:
>>
>>            EXTRA_CFLAGS='-g $(OPT_FLAGS) $(SAN_CFLAGS) $(EXTRA_CFLAGS)' \
>>
>> is there a reason why this is not respected and -O0 and -fPIC are
>> hard-coded?
> Yes it is true that there is no good reason. I will fix it in the next version.
> 
>> What if someone wants to build selftests (including libbpf)
>> with -O2 and some additional flags?
> I will add a flag such as OPT_FLAGS ?= $(if $(RELEASE),-O2,O0), which follows
> the pattern in the bpf/Makefile:37. So if we run 
> $ make -> -g -O0 -fPIC (taget libbpf) and -g -O0 (host bpftool)
> $ make RELEASE=1 -> -g -O2 -fPIC (taget libbpf) and -g -O2 (host bpftool)
> 
>> Is that possible with the new
>> lib.bpf.mk? It would be nice if it used at least EXTRA_CFLAGS or
>> USERCFLAGS defined in lib.mk.
> Good idea. I will add the EXTRA_CFLAGS for target libbpf, host libbpf and host
> bpgtool. Such that: 
> $ make OPT_FLAGS=-O2 EXTRA_CFLAGS=-DFOO -> -g -O2 -fPIC -DFOO (for target
> libbpf) and -g -O2 -DFOO (for host bpftool)

I'm wondering if we could use USERCFLAGS (and USERLDFLAGS) instead.
These seem to be the preferred way for all selftests, per
tools/testing/selftests/lib.mk:

    # Enables to extend CFLAGS and LDFLAGS from command line, e.g.
    # make USERCFLAGS=-Werror USERLDFLAGS=-static
    CFLAGS += $(USERCFLAGS)
    LDFLAGS += $(USERLDFLAGS)

At the time I was adding the extra flags to libbpf/bpftool sub-makes, I
wasn't aware of USER*FLAGS so I used EXTRA_*FLAGS instead. But now, when
someone wants to build multiple selftest collections with extra flags,
they need to define both. For instance, building with PIE requires:

    make -C tools/testing/selftests TARGETS="bpf ..." \
        USERCFLAGS=-fpie EXTRA_CFLAGS=-fpie \
        USERLDFLAGS=-pie EXTRA_LDFLAGS=-pie \

Switching to USER*FLAGS for bpf selftests would simplify things a bit.

Viktor

> 
>>
>> Same questions would apply to other rules for libbpf and bpftool below.
> I would check it them as as well in next version.
> 
>> Thanks!
>> Viktor
>>
>>
> Thanks for your time and reviewing. Please let me know your concerns. Thanks!
> 
> Best,
> Ziyang