Re: [BUG] bpf: tcp: bpf_tcp_ops_set_rcvlowat() missing from BTF with clang KCSAN

[Breno Leitao <leitao@debian.org>]

On Fri, Nov 06, 2026 at 07:05:25PM +0000, Kuniyuki Iwashima wrote:
> On Fri, 06 Nov 2026 07:58:01 -0800, Breno Leitao wrote:
> > On Fri, Nov 06, 2026 at 09:16:24PM +0800, Jiayuan Chen wrote:
> > > Thanks for the report !
> > > 
> > > 
> > > On 11/6/26 7:38 PM, Breno Leitao wrote:
> > > > My arm64 KCSAN builds of linux-next fail since next-20261015, because
> > > > bpf_tcp_ops_set_rcvlowat() is missing from the vmlinux BTF:
> > > >
> > > >   WARN: resolve_btfids: no BTF func for kfunc bpf_tcp_ops_set_rcvlowat in bpf_tcp_ops_set_rcvlowat_kfunc_set
> > > >   WARN: resolve_btfids: unresolved symbol bpf_tcp_ops_set_rcvlowat
> > > >   Failed to generate BTF for vmlinux
> > > >   Try to disable CONFIG_DEBUG_INFO_BTF
> > > >   make[4]: *** [scripts/Makefile.vmlinux:72: vmlinux.unstripped] Error 1
> > > 
> > > 
> > > 
> > > Has pahole fixed this issue?
> > 
> > I don't think so, see the line below:
> 
> Could you try this ?

Thanks, it fixes my build. I tested it on top of pahole master (9eb594d)
with next-20261105 and clang 22.1.3:

 - arm64 KCSAN, CONFIG_WERROR=y: vmlinux links again,
   bpf_tcp_ops_set_rcvlowat() is back in BTF, __bpf_tcp_ops_init()
   returns 0, and progs/tcp_autolowat.c from the selftests loads.

 - It also brings back scx_bpf_tid_to_task() that was work arounded by
   tejun.

Feel free to add my "Tested-by: Breno Leitao <leitao@debian.org>" tag.

--breno