netdev - Re: [PATCH bpf-next] libbpf: provide more helpful message on uninitialized global var

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Message-ID: <CAEf4Bza_CgAvfSOmPPPR9Q+FVct2QkXyzo3UgJf1X0rkR1oK2w@mail.gmail.com>
Date:   Tue, 23 Jul 2019 10:33:34 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     Andrii Nakryiko <andriin@...com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next] libbpf: provide more helpful message on
 uninitialized global var

On Tue, Jul 23, 2019 at 1:51 AM Song Liu <songliubraving@...com> wrote:
>
>
>
> > On Jul 22, 2019, at 9:23 PM, Andrii Nakryiko <andriin@...com> wrote:
> >
> > When BPF program defines uninitialized global variable, it's put into
> > a special COMMON section. Libbpf will reject such programs, but will
> > provide very unhelpful message with garbage-looking section index.
> >
> > This patch detects special section cases and gives more explicit error
> > message.
> >
> > Signed-off-by: Andrii Nakryiko <andriin@...com>
> > ---
> > tools/lib/bpf/libbpf.c | 14 +++++++++++---
> > 1 file changed, 11 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 794dd5064ae8..5f9e7eedb134 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -1760,15 +1760,23 @@ bpf_program__collect_reloc(struct bpf_program *prog, GElf_Shdr *shdr,
> >                        (long long) sym.st_value, sym.st_name, name);
> >
> >               shdr_idx = sym.st_shndx;
> > +             insn_idx = rel.r_offset / sizeof(struct bpf_insn);
> > +             pr_debug("relocation: insn_idx=%u, shdr_idx=%u\n",
> > +                      insn_idx, shdr_idx);
> > +
> > +             if (shdr_idx >= SHN_LORESERVE) {
> > +                     pr_warning("relocation: not yet supported relo for non-static global \'%s\' variable "
> > +                                "in special section (0x%x) found in insns[%d].code 0x%x\n",
>
> For easy grep, we should keep this one long long string.

I was worried it's way too long, so split it. But yeah, I'll just
merge it back into single line, thanks!

>
> Thanks,
> Song