linux-kernel - Re: [RFC PATCH v10 11/50] bpf tools: Collect symbol table from SHT

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Date:	Tue, 7 Jul 2015 12:10:17 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	ast@...mgrid.com, brendan.d.gregg@...il.com, daniel@...earbox.net,
	namhyung@...nel.org, masami.hiramatsu.pt@...achi.com,
	paulus@...ba.org, a.p.zijlstra@...llo.nl, mingo@...hat.com,
	jolsa@...nel.org, dsahern@...il.com, linux-kernel@...r.kernel.org,
	lizefan@...wei.com, hekuang@...wei.com, xiakaixu@...wei.com,
	pi3orama@....com
Subject: Re: [RFC PATCH v10 11/50] bpf tools: Collect symbol table from
 SHT_SYMTAB section

Em Wed, Jul 01, 2015 at 02:13:59AM +0000, Wang Nan escreveu:
> This patch collects symbols section. This section is useful when
> linking ELF maps.

I guess it is, but could you ellaborate on this? I.e. _how_ is this
useful? I can imagine some ways, but would be nice if you outlined what
is the first thing you will do with this, as a justification for this
patch.

I am applying the patches, compile testing them and will try the end
result, but please consider being more verbose in the justification for
each patch, not requiring the reviewer to go on looking at other patches
to figure out what a patch is good for.

I will happily 'git commit -i' the patches to amend the patch
descriptions.

This is valid for me of for anybody else trying to make sense of your
patches.

- Arnaldo
 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> Acked-by: Alexei Starovoitov <ast@...mgrid.com>
> ---
>  tools/lib/bpf/libbpf.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 87f5054..9b016c0 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -94,6 +94,7 @@ struct bpf_object {
>  		size_t obj_buf_sz;
>  		Elf *elf;
>  		GElf_Ehdr ehdr;
> +		Elf_Data *symbols;
>  	} efile;
>  	char path[];
>  };
> @@ -135,6 +136,7 @@ static void bpf_object__elf_finish(struct bpf_object *obj)
>  		elf_end(obj->efile.elf);
>  		obj->efile.elf = NULL;
>  	}
> +	obj->efile.symbols = NULL;
>  	zclose(obj->efile.fd);
>  	obj->efile.obj_buf = NULL;
>  	obj->efile.obj_buf_sz = 0;
> @@ -333,6 +335,14 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
>  		else if (strcmp(name, "maps") == 0)
>  			err = bpf_object__init_maps(obj, data->d_buf,
>  						    data->d_size);
> +		else if (sh.sh_type == SHT_SYMTAB) {
> +			if (obj->efile.symbols) {
> +				pr_warning("bpf: multiple SYMTAB in %s\n",
> +					   obj->path);
> +				err = -EEXIST;
> +			} else
> +				obj->efile.symbols = data;
> +		}
>  		if (err)
>  			goto out;
>  	}
> -- 
> 1.8.3.4
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