linux-kernel - Re: [RFC PATCH v3 2/2] bpf: Introduce function for outputing data to perf event

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Date:	Tue, 07 Jul 2015 18:45:04 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	He Kuang <hekuang@...wei.com>, rostedt@...dmis.org,
	masami.hiramatsu.pt@...achi.com, acme@...nel.org,
	a.p.zijlstra@...llo.nl, mingo@...hat.com, namhyung@...nel.org,
	jolsa@...nel.org
CC:	wangnan0@...wei.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 2/2] bpf: Introduce function for outputing data
 to perf event

On 7/7/15 4:43 AM, He Kuang wrote:

> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -210,6 +210,9 @@ enum bpf_func_id {
>   	 * Return: 0 on success
>   	 */
>   	BPF_FUNC_l4_csum_replace,
> +
> +	/* int bpf_output_data(void *src, int size, void *regs) */

bpf_output_trace_data(struct pt_regs *ctx, void *data, int data_size)

> +	BPF_FUNC_output_data,
>   	__BPF_FUNC_MAX_ID,
>   };
>
> +static u64 bpf_output_data(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
> +{
> +	void *src = (void *) (long) r1;
> +	int dsize = (int) r2, __size, size;
> +	void *regs = (void *) (long) r3;

please cast to 'struct pt_regs *', since that's what it is.

> +	__size = sizeof(*entry) + dsize;
> +	size = ALIGN(__size + sizeof(u32), sizeof(u64));
> +	size -= sizeof(u32);
> +
> +	entry = perf_trace_buf_prepare(size, TRACE_BPF, NULL, &rctx);
> +	if (!entry)
> +		return -ENOMEM;
> +
> +	entry->size = dsize;

something wrong here. Either 'size' from bpf_trace_entry_head
should be used or from trace_bpf.

>   	(void *) BPF_FUNC_l4_csum_replace;
> +static int (*bpf_output_data)(void *src, int size, void *regs) =
> +	(void *) BPF_FUNC_output_data;

'struct pt_regs *ctx' here as well.

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