linux-kernel - Re: [RFC PATCH v3 16/37] bpf tools: Collect eBPF programs from their own sections

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Date:	Mon, 18 May 2015 21:29:22 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	paulus@...ba.org, a.p.zijlstra@...llo.nl, mingo@...hat.com,
	acme@...nel.org, jolsa@...nel.org, dsahern@...il.com,
	ast@...mgrid.com, daniel@...earbox.net, brendan.d.gregg@...il.com,
	masami.hiramatsu.pt@...achi.com, lizefan@...wei.com,
	linux-kernel@...r.kernel.org, pi3orama@....com
Subject: Re: [RFC PATCH v3 16/37] bpf tools: Collect eBPF programs from their
 own sections

Hi,

On Sun, May 17, 2015 at 10:56:41AM +0000, Wang Nan wrote:
> This patch collects all programs in an object file into an array of
> 'struct bpf_program' for further processing. That structure is for
> representing each eBPF program. 'bpf_prog' should be a better name, but
> it has been used by linux/filter.h. Although it is a kernel space name,
> I still prefer to call it 'bpf_program' to prevent possible confusion.
> 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> ---

[SNIP]

> +static struct bpf_program *
> +bpf_program_alloc(struct bpf_object *obj, void *data, size_t size,
> +		  char *name, int idx)
> +{
> +	struct bpf_program *prog, *progs;
> +	int nr_progs;
> +
> +	if (size < sizeof(struct bpf_insn)) {
> +		pr_warning("corrupted section '%s'\n", name);
> +		return NULL;
> +	}
> +	
> +	progs = obj->programs;
> +	nr_progs = obj->nr_programs;
> +
> +	progs = realloc(progs, sizeof(*prog) * (nr_progs + 1));
> +	if (!progs) {
> +		/*
> +		 * In this case the original obj->programs
> +		 * is still valid, so don't need special treat for
> +		 * bpf_close_object().
> +		 */
> +		pr_warning("failed to alloc a new program '%s'\n",
> +			   name);
> +		return NULL;
> +	}
> +
> +	obj->programs = progs;
> +
> +	prog = &progs[nr_progs];
> +	bzero(prog, sizeof(*prog));
> +
> +	obj->nr_programs = nr_progs + 1;
> +
> +	prog->section_name = strdup(name);
> +	if (!prog->section_name) {
> +		pr_warning("failed to alloc name for prog %s\n",
> +			   name);
> +		goto out;
> +	}
> +
> +	prog->insns = malloc(size);
> +	if (!prog->insns) {
> +		pr_warning("failed to alloc insns for %s\n", name);
> +		goto out;
> +	}
> +	prog->insns_cnt = size / sizeof(struct bpf_insn);
> +	memcpy(prog->insns, data,
> +	       prog->insns_cnt * sizeof(struct bpf_insn));

Doesn't the data need to be swapped?

Thanks,
Namhyung


> +	prog->idx = idx;
> +
> +	return prog;
> +out:
> +	bpf_clear_program(prog);
> +	return NULL;
> +}
> +
>  static struct bpf_object *__bpf_obj_alloc(const char *path)
>  {
>  	struct bpf_object *obj;
> @@ -380,6 +468,22 @@ static int bpf_obj_elf_collect(struct bpf_object *obj)
>  				err = -EEXIST;
>  			} else
>  				obj->elf.symbols = data;
> +		} else if ((sh.sh_type == SHT_PROGBITS) &&
> +			   (sh.sh_flags & SHF_EXECINSTR) &&
> +			   (data->d_size > 0)) {
> +			struct bpf_program *prog;
> +
> +			prog = bpf_program_alloc(obj, data->d_buf,
> +						 data->d_size, name,
> +						 idx);
> +			if (!prog) {
> +				pr_warning("failed to alloc "
> +					   "program %s (%s)", name,
> +					   obj->path);
> +				err = -ENOMEM;
> +			} else
> +				pr_debug("found program %s\n",
> +					 prog->section_name);
>  		}
>  		if (err)
>  			goto out;
> @@ -446,5 +550,12 @@ void bpf_close_object(struct bpf_object *obj)
>  		free(obj->maps_buf);
>  	if (obj->config_str)
>  		free(obj->config_str);
> +	if (obj->programs) {
> +		size_t i;
> +
> +		for (i = 0; i < obj->nr_programs; i++)
> +			bpf_clear_program(&obj->programs[i]);
> +		free(obj->programs);
> +	}
>  	free(obj);
>  }
> -- 
> 1.8.3.4
> 
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