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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Mon, Nov 09, 2026 at 04:33:40AM -0800, Breno Leitao wrote:
> 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.

thanks, I'll check this later today,

- Arnaldo