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Date:   Mon, 4 Mar 2019 19:36:14 +0000
From:   Song Liu <songliubraving@...com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     Networking <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "acme@...hat.com" <acme@...hat.com>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "namhyung@...nel.org" <namhyung@...nel.org>
Subject: Re: [PATCH v5 perf,bpf 07/15] perf, bpf: save bpf_prog_info
 information as headers to perf.data



> On Mar 4, 2019, at 5:52 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> 
> On Wed, Feb 27, 2019 at 09:06:35PM -0800, Song Liu wrote:
> 
> SNIP
> 
>> +static int process_bpf_prog_info(struct feat_fd *ff,
>> +				 void *data __maybe_unused)
>> +{
>> +	struct bpf_prog_info_linear *info_linear;
>> +	struct bpf_prog_info_node *info_node;
>> +	struct perf_env *env = &ff->ph->env;
>> +	u32 count, i;
>> +	int err = -1;
>> +
>> +	if (do_read_u32(ff, &count))
>> +		return -1;
>> +
>> +	down_write(&env->bpf_progs.lock);
>> +
>> +	for (i = 0; i < count; ++i) {
>> +		u32 info_len, data_len;
>> +
>> +		info_linear = NULL;
>> +		info_node = NULL;
>> +		if (do_read_u32(ff, &info_len))
>> +			goto out;
>> +		if (do_read_u32(ff, &data_len))
>> +			goto out;
>> +
>> +		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 */
>> +		if (ff->ph->needs_swap) {
>> +			free(info_linear);
>> +			continue;
>> +		}
> 
> so in this case we can check for needs_swap in the begining
> of the function and bail out without reading all the data

If we bail out, perf-record will fail. If we read all the data 
but ignore them, perf-record will continue without bpf annotation 
support. I think the latter is a better experience with little 
effort here. 

> 
> also please display soem error message saying we don't support
> ebpf progs data report over the different endianity

I will add a warning in the next version. 

Thanks,
Song

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