Re: [PATCH bpf-next v1 01/14] selftests/bpf: Pass through build flags to bpftool and resolve_btfids

[Ihor Solodrai]

On 2/11/26 6:39 PM, Alexei Starovoitov wrote:
> On Wed, Feb 11, 2026 at 5:14 PM Ihor Solodrai <ihor.solodrai@xxxxxxxxx> wrote:
>>
>> EXTRA_* and SAN_* build flags were not correctly propagated to bpftool
>> and resolve_btids when building selftests/bpf. This led to various
>> build errors on attempt to build with SAN_CFLAGS="-fsanitize=address",
>> for example.
>>
>> Fix the makefiles to address this:
>>   - Pass SAN_CFLAGS/SAN_LDFLAGS to bpftool and resolve_btfids build
>>   - Propagate EXTRA_LDFLAGS to resolve_btfids link command
>>   - Use pkg-config to detect zlib and zstd for resolve_btfids, similar
>>     libelf handling
>>
>> Signed-off-by: Ihor Solodrai <ihor.solodrai@xxxxxxxxx>
>> ---
>>  tools/bpf/resolve_btfids/Makefile    | 7 +++++--
>>  tools/testing/selftests/bpf/Makefile | 9 +++++----
>>  2 files changed, 10 insertions(+), 6 deletions(-)
>>
>> diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
>> index 1733a6e93a07..ef083602b73a 100644
>> --- a/tools/bpf/resolve_btfids/Makefile
>> +++ b/tools/bpf/resolve_btfids/Makefile
>> @@ -65,6 +65,9 @@ $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU
>>  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
>>  LIBELF_LIBS  := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
>>
>> +ZLIB_LIBS  := $(shell $(HOSTPKG_CONFIG) zlib --libs 2>/dev/null || echo -lz)
>> +ZSTD_LIBS  := $(shell $(HOSTPKG_CONFIG) libzstd --libs 2>/dev/null || echo -lzstd)
> 
> The first two patches look serious enough and justify going to bpf tree.
> The rest can probably go via bpf as well, since we're early
> in the merge window.
> Would be great to have some Acks first though.
> 
> Why add zstd here? It's not used by resolve_btfid. Why add it?

IIRC zstd is a transitive dependency of libelf.

I stumbled on a combination of build flags that caused link errors
because of this missing.  I can find or produce an example log later
if that'd be helpful.