linux-kernel - Re: [PATCH v4 perf,bpf 07/15] perf, bpf: save bpf_prog

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Message-ID: <6D86D79B-6E72-4E42-86F8-41D1357229BF@fb.com>
Date:   Wed, 27 Feb 2019 17:28:06 +0000
From:   Song Liu <songliubraving@...com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     Netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v4 perf,bpf 07/15] perf, bpf: save bpf_prog_info
 information as headers to perf.data



> On Feb 27, 2019, at 5:21 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> 
> On Mon, Feb 25, 2019 at 04:20:11PM -0800, Song Liu wrote:
> 
> SNIP
> 
>> +		if (info_len > sizeof(struct bpf_prog_info)) {
>> +			pr_warning("detected invalid bpf_prog_info\n");
>> +			goto out;
>> +		}
>> +
>> +		info_linear = malloc(sizeof(struct bpf_prog_info_linear) +
>> +				     data_len);
>> +		if (!info_linear)
>> +			goto out;
>> +		info_linear->info_len = sizeof(struct bpf_prog_info);
>> +		info_linear->data_len = data_len;
>> +		if (do_read_u64(ff, (u64 *)(&info_linear->arrays)))
>> +			goto out;
>> +		if (__do_read(ff, &info_linear->info, info_len))
>> +			goto out;
>> +		if (info_len < sizeof(struct bpf_prog_info))
>> +			memset(((void *)(&info_linear->info)) + info_len, 0,
>> +			       sizeof(struct bpf_prog_info) - info_len);
>> +
>> +		if (__do_read(ff, info_linear->data, data_len))
>> +			goto out;
>> +
>> +		/* endian mismatch, drop the info, continue */
> 
> so there's no way we can swap the data? why?
> 
> jirka

Yes, we can swap the data. OTOH, the set is big enough. How about we 
implement the swap later? Running perf-report on a system of with 
different endianness is a relatively rare case. 

Thanks,
Song



>> +		if (ff->ph->needs_swap) {
>> +			free(info_linear);
>> +			continue;
>> +		}
> 
> SNIP