netdev - Re: [PATCH bpf-next] tools/resolve_btfids: Warn when having multiple IDs for single type

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Date:   Tue, 5 Jan 2021 23:47:28 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        Qais Yousef <qais.yousef@....com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH bpf-next] tools/resolve_btfids: Warn when having multiple
 IDs for single type

On Tue, Jan 05, 2021 at 01:15:39PM -0800, Andrii Nakryiko wrote:
> On Tue, Jan 5, 2021 at 7:41 AM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > The kernel image can contain multiple types (structs/unions)
> > with the same name. This causes distinct type hierarchies in
> > BTF data and makes resolve_btfids fail with error like:
> >
> >   BTFIDS  vmlinux
> > FAILED unresolved symbol udp6_sock
> >
> > as reported by Qais Yousef [1].
> >
> > This change adds warning when multiple types of the same name
> > are detected:
> >
> >   BTFIDS  vmlinux
> > WARN: multiple IDs found for 'file' (526, 113351)
> > WARN: multiple IDs found for 'sk_buff' (2744, 113958)
> >
> > We keep the lower ID for the given type instance and let the
> > build continue.
> >
> > [1] https://lore.kernel.org/lkml/20201229151352.6hzmjvu3qh6p2qgg@e107158-lin/
> > Reported-by: Qais Yousef <qais.yousef@....com>
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> 
> see comments below, but otherwise lgtm
> 
> Acked-by: Andrii Nakryiko <andrii@...nel.org>
> 
> >  tools/bpf/resolve_btfids/main.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
> > index e3ea569ee125..36a3b1024cdc 100644
> > --- a/tools/bpf/resolve_btfids/main.c
> > +++ b/tools/bpf/resolve_btfids/main.c
> > @@ -139,6 +139,8 @@ int eprintf(int level, int var, const char *fmt, ...)
> >  #define pr_debug2(fmt, ...) pr_debugN(2, pr_fmt(fmt), ##__VA_ARGS__)
> >  #define pr_err(fmt, ...) \
> >         eprintf(0, verbose, pr_fmt(fmt), ##__VA_ARGS__)
> > +#define pr_info(fmt, ...) \
> > +       eprintf(0, verbose, pr_fmt(fmt), ##__VA_ARGS__)
> 
> how is it different from pr_err? Did you forget to update verboseness
> levels or it's intentional?

intentional, I'm using pr_err to print in error paths,
so I wanted to add new one for other 'info' messages without -v

> 
> >
> >  static bool is_btf_id(const char *name)
> >  {
> > @@ -526,8 +528,13 @@ static int symbols_resolve(struct object *obj)
> >
> >                 id = btf_id__find(root, str);
> >                 if (id) {
> > -                       id->id = type_id;
> > -                       (*nr)--;
> > +                       if (id->id) {
> > +                               pr_info("WARN: multiple IDs found for '%s' (%d, %d)\n",
> > +                                       str, id->id, type_id);
> > +                       } else {
> > +                               id->id = type_id;
> > +                               (*nr)--;
> 
> btw, there is a nasty shadowing of nr variable, which is used both for
> the for() loop condition (as int) and as `int *` inside the loop body.
> It's better to rename inner (or outer) nr, it's extremely confusing as
> is.

nice, I'll change that

thanks,
jirka

> 
> > +                       }
> >                 }
> >         }
> >
> > --
> > 2.26.2
> >
>