linux-kernel - Re: [RFC/PATCH] perf: Add sizeof operator support

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Message-ID: <20160617121736.023f009f@gandalf.local.home>
Date:	Fri, 17 Jun 2016 12:17:36 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jeremy Linton <jeremy.linton@....com>
Cc:	linux-kernel@...r.kernel.org, acme@...hat.com, namhyung@...nel.org,
	kapileshwar.singh@....com, scottwood@...escale.com,
	hekuang@...wei.com
Subject: Re: [RFC/PATCH] perf: Add sizeof operator support

On Tue, 14 Jun 2016 11:38:32 -0500
Jeremy Linton <jeremy.linton@....com> wrote:

> There are a fair number of tracepoints in the kernel making
> use of the sizeof operator. Allow perf to understand some of
> those cases, and report a more informative error message for
> the ones it cannot understand.
> 
> Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> ---
> 
> So this is as much a RFC as a patch because the use of sizeof
> seems to extend to structures, pointers, etc that aren't easy
> to deduce from userspace. I'm not sure what the correct solution
> should be in those cases.
> 
>  tools/lib/traceevent/event-parse.c | 46 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
> index a8b6357..5813248 100644
> --- a/tools/lib/traceevent/event-parse.c
> +++ b/tools/lib/traceevent/event-parse.c
> @@ -31,6 +31,8 @@
>  #include <errno.h>
>  #include <stdint.h>
>  #include <limits.h>
> +#include <linux/kernel.h>
> +#include <linux/types.h>
>  
>  #include <netinet/ip6.h>
>  #include "event-parse.h"
> @@ -2868,6 +2870,46 @@ process_str(struct event_format *event __maybe_unused, struct print_arg *arg,
>  }
>  
>  static enum event_type
> +process_sizeof(struct event_format *event __maybe_unused, struct print_arg *arg,
> +	       char **tok)
> +{
> +	char *token;
> +	char *atom;
> +
> +	if (process_paren(event, arg, &token) < 0)
> +		goto out_free;
> +
> +	atom = arg->atom.atom;
> +	if (arg->type != PRINT_ATOM) {
> +		do_warning_event(event, "didn't understand %s for sizeof\n",
> +				 token);
> +		goto out_free_atom;
> +	}
> +
> +	if (strcmp(token, "__u64") == 0) {
> +		if (asprintf(&arg->atom.atom, "%zd", sizeof(__u64)) < 0)
> +			goto out_free_atom;
> +	} else if (strcmp(token, "__u32") == 0) {
> +		if (asprintf(&arg->atom.atom, "%zd", sizeof(__u32)) < 0)
> +			goto out_free_atom;

What events are doing sizeof(__u64) and sizeof(__u32)?

First, that's useless, as sizeof(__u64) will always be 8, and
sizeof(__u32) will always be 4.

What exactly is this fixing?

-- Steve


> +	} else {
> +		do_warning_event(event, "unknown sizeof %s\n", token);
> +		goto out_free_atom;
> +	}
> +
> +	free(atom);
> +	*tok = token;
> +	return EVENT_DELIM;
> +
> + out_free_atom:
> +	free_token(atom);
> + out_free:
> +	free_token(token);
> +	*tok = NULL;
> +	return EVENT_ERROR;
> +}
> +
> +static enum event_type
>  process_bitmask(struct event_format *event __maybe_unused, struct print_arg *arg,
>  	    char **tok)
>  {
> @@ -3026,6 +3068,10 @@ process_function(struct event_format *event, struct print_arg *arg,
>  		free_token(token);
>  		return process_dynamic_array_len(event, arg, tok);
>  	}
> +	if (strcmp(token, "sizeof") == 0) {
> +		free_token(token);
> +		return process_sizeof(event, arg, tok);
> +	}
>  
>  	func = find_func_handler(event->pevent, token);
>  	if (func) {