Re: [PATCH bpf-next] Fix undefined symbol references for module build post cnum changes

[Alan Maguire <alan.maguire@oracle.com>]

On 27/04/2026 18:11, Alexei Starovoitov wrote:
> On Mon, Apr 27, 2026 at 6:07 PM Eduard Zingerman <eddyz87@gmail.com> wrote:
>>
>> On Mon, 2026-04-27 at 09:44 -0700, Eduard Zingerman wrote:
>>> On Mon, 2026-04-27 at 12:22 +0100, Alan Maguire wrote:
>>>> Seeing the following on bpf-next:
>>>>
>>>>  DESCEND objtool
>>>>   DESCEND bpf/resolve_btfids
>>>>   INSTALL libsubcmd_headers
>>>>   INSTALL libsubcmd_headers
>>>>   MODPOST Module.symvers
>>>> ERROR: modpost: "cnum64_umin" [drivers/net/ethernet/netronome/nfp/nfp.ko] undefined!
>>>> ERROR: modpost: "cnum64_umax" [drivers/net/ethernet/netronome/nfp/nfp.ko] undefined!
>>>> make[2]: *** [scripts/Makefile.modpost:147: Module.symvers] Error 1
>>>> make[1]: *** [bpf-next/Makefile:2089: modpost] Error 2
>>>> make: *** [Makefile:248: __sub-make] Error 2
>>>>
>>>> Further investigation suggests nfp indeed does pull in those symbols,
>>>> likely due to references in include/linux/bpf_verifier.h:
>>>>
>>>> static inline s64 reg_smax(const struct bpf_reg_state *reg)
>>>> {
>>>>         return cnum64_smax(reg->r64);
>>>> }
>>>>
>>>> static inline u64 reg_umin(const struct bpf_reg_state *reg)
>>>> {
>>>>         return cnum64_umin(reg->r64);
>>>> }
>>>>
>>>> ...
>>>>
>>>> Export symbols for these references.
>>>>
>>>> Reported-by: Kaitao Cheng <pilgrimtao@gmail.com>
>>>> Fixes: bbc631085503 ("bpf: replace min/max fields with struct cnum{32,64}")
>>>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>>>> ---
>>>
>>> Hi Alan,
>>>
>>> thank you for the fix, apologies for breaking this.
>>>
>>> Acked-by: Eduard Zingerman <eddyz87@gmail.com>
>>
>> However, Alexei raises a valid question.
>> Netronome code uses the following accessors:
>> - cnum{32,64}_reg_umin
>> - cnum{32,64}_reg_umax
>>
>> However, this patch also exports the following on top:
>> - cnum{32,64}_from_{urange,srange}
>> - cnum{32,64}_reg_smin
>> - cnum{32,64}_reg_smax
>>
>> Why export extra accessors?
> 
> I left only 2 while applying and rewrote commit log.

Yep, I just added the accessors as they are potentially available to consumers
via bpf_verifier.h. No actual users today though as far as I could see. Thanks!