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

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Date:   Tue, 23 Jul 2019 08:51:02 +0000
From:   Song Liu <songliubraving@...com>
To:     Andrii Nakryiko <andriin@...com>
CC:     "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>,
        "andrii.nakryiko@...il.com" <andrii.nakryiko@...il.com>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next] libbpf: provide more helpful message on
 uninitialized global var



> 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. 

Thanks,
Song