linux-kernel - Re: [RFC PATCH v3 18/37] bpf tools: Record map accessing instructions for each program

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Date:	Mon, 18 May 2015 11:34:43 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Wang Nan <wangnan0@...wei.com>, paulus@...ba.org,
	a.p.zijlstra@...llo.nl, mingo@...hat.com, acme@...nel.org,
	namhyung@...nel.org, jolsa@...nel.org, dsahern@...il.com,
	daniel@...earbox.net, brendan.d.gregg@...il.com,
	masami.hiramatsu.pt@...achi.com
CC:	lizefan@...wei.com, linux-kernel@...r.kernel.org, pi3orama@....com
Subject: Re: [RFC PATCH v3 18/37] bpf tools: Record map accessing instructions
 for each program

On 5/17/15 3:56 AM, Wang Nan wrote:
> This patch records the indics of instructions which are needed to be
> relocated. Those information are saved in 'reloc_desc' field in
> 'struct bpf_program'. In loading phase (this patch takes effect in
> opening phase), the collected instructions will be replaced by
> map loading instructions.
>
> Since we are going to close the ELF file and clear all data at the end
> of 'opening' phase, ELF information will no longer be valid in
> 'loading' phase. We have to locate the instructions before maps are
> loaded, instead of directly modifying the instruction.
>
> 'struct bpf_map_def' is introduce in this patch to let us know how many
> maps defined in the object.
>
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
...
> +/*
> + * packed attribute is unnecessary for 'bpf_map_def'.
> + */
> +struct bpf_map_def {
> +	unsigned int type;
> +	unsigned int key_size;
> +	unsigned int value_size;
> +	unsigned int max_entries;
> +};

the comment looks out of place. 'packed' is necessary somewhere else?
What were you concerned about here?

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