On Sat, Nov 20, 2021 at 12:46:58AM IST, Kumar Kartikeya Dwivedi wrote: > On Wed, Nov 17, 2021 at 10:50:43AM IST, Andrii Nakryiko wrote: > > On Mon, Nov 15, 2021 at 11:18 AM Kumar Kartikeya Dwivedi > > <memxor@xxxxxxxxx> wrote: > > > > > > resolve_btfids prints a warning when it finds an unresolved symbol, > > > (id == 0) in id_patch. This can be the case for BTF sets that are empty > > > (due to disabled config options), hence printing warnings for certain > > > builds, most recently seen in [0]. Hence, demote the warning to debug > > > log level to avoid build time noise. > > > > > > [0]: https://lore.kernel.org/all/1b99ae14-abb4-d18f-cc6a-d7e523b25542@xxxxxxxxx > > > > > > Fixes: 0e32dfc80bae ("bpf: Enable TCP congestion control kfunc from modules") > > > Reported-by: Pavel Skripkin <paskripkin@xxxxxxxxx> > > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> > > > --- > > > tools/bpf/resolve_btfids/main.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c > > > index a59cb0ee609c..833bfcc9ccf6 100644 > > > --- a/tools/bpf/resolve_btfids/main.c > > > +++ b/tools/bpf/resolve_btfids/main.c > > > @@ -569,7 +569,7 @@ static int id_patch(struct object *obj, struct btf_id *id) > > > int i; > > > > > > if (!id->id) { > > > - pr_err("WARN: resolve_btfids: unresolved symbol %s\n", id->name); > > > + pr_debug("WARN: resolve_btfids: unresolved symbol %s\n", id->name); > > > > This is an important warning that helps detect some misconfiguration, > > we cannot just hide it. If it really is happening for empty lists > > (why?), we should handle empty lists better, but not hide the warning. > > > > +Cc Jiri > > Sorry for the delay. The 'why' is because in case of empty BTF set, the id->cnt > aliasing over id->id (for non-set __BTF_ID_*) is zero, so it trips over when it > sees it as 0 for empty set in id_patch. > > So, what would be your opinion on how to handle this case? Ignore the warning > case for empty sets specifically? (e.g. using string comparison in id_patch for > id->name, or split id and cnt out of union and assign non-zero to id in case cnt Ah, I realized after sending that actually would be far more work (and also confusing/error prone), since it is copied to ptr[idx] as id->id once in id_patch and then used as cnt for sorting in sets_patch, which would break qsort. Just recording that it is a set in btf_id struct might be better. -- Kartikeya
