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

Steven Rostedt
2016-06-17T16:17:48Z

On Tue, 14 Jun 2016 11:38:32 -0500
Jeremy Linton <jeremy.linton@arm.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@arm.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) {