linux-kernel - Re: [PATCH v2 13/13] perf tools: add feature header record to pipe-mode

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Date:   Thu, 25 May 2017 10:10:04 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     David Carrillo-Cisneros <davidcc@...gle.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>, Simon Que <sque@...omium.org>,
        Wang Nan <wangnan0@...wei.com>, Jiri Olsa <jolsa@...nel.org>,
        He Kuang <hekuang@...wei.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        David Ahern <dsa@...ulusnetworks.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH v2 13/13] perf tools: add feature header record to
 pipe-mode

On Tue, May 23, 2017 at 12:48:53AM -0700, David Carrillo-Cisneros wrote:

SNIP

> +int perf_event__synthesize_features(struct perf_tool *tool,
> +				    struct perf_session *session,
> +				    struct perf_evlist *evlist,
> +				    perf_event__handler_t process)
> +{
> +	struct perf_header *header = &session->header;
> +	struct feat_fd fdd;
> +	struct feature_event *fe;
> +	size_t sz, sz_hdr;
> +	int feat, ret;
> +
> +	sz_hdr = sizeof(fe->header);
> +	sz = sizeof(union perf_event);
> +	/* get a nice alignment */
> +	sz = PERF_ALIGN(sz, getpagesize());
> +
> +	memset(&fdd, 0, sizeof(fdd));
> +
> +	fdd.buf = malloc(sz);
> +	if (!fdd.buf)
> +		return -ENOMEM;
> +
> +	fdd.size = sz - sz_hdr;
> +
> +	for_each_set_bit(feat, header->adds_features, HEADER_FEAT_BITS) {
> +		if (!feat_ops[feat].has_record) {
> +			pr_debug("No record header feature for header :%d\n", feat);
> +			continue;
> +		}
> +
> +		fdd.offset = sizeof(*fe);
> +
> +		ret = feat_ops[feat].write(&fdd, evlist);
> +		if (ret || fdd.offset <= (ssize_t)sizeof(*fe)) {
> +			pr_debug("Error writing feature\n");
> +			continue;
> +		}
> +
> +		/* fdd.buf may have changed due to realloc in do_write() */

right, so how's ensured the data never cross the maximum event size (0xffff) ?

I think do_write should have some check on that

jirka