linux-kernel - Re: [PATCH] perf trace: Handle legacy syscalls

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Message-ID: <20150320153226.GI16485@kernel.org>
Date:	Fri, 20 Mar 2015 12:32:26 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	David Ahern <dsahern@...il.com>
Cc:	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH] perf trace: Handle legacy syscalls

Em Thu, Mar 19, 2015 at 12:36:21PM -0600, David Ahern escreveu:
> Currently the code skips the first field with the expectation that it is
> 'nr'. But older kernels do not have the 'nr' field:
> 
>     field:int nr;   offset:8;   size:4; signed:1;
> 
> Change perf-trace to drop the field if it exists after parsing the format
> file.
> 
> This fixes the off-by-one problem with older kernels (e.g., RHEL6). e.g,
> perf-trace shows this for write:
> 
>     1.515 ( 0.006 ms): dd/4245 write(buf: 2</dev/pts/0>, count: 140733837536224                      ) = 26
> 
> where 2 is really the fd, the huge number is really the buf address, etc.
> With this patch you get the more appropriate:
> 
>     1.813 ( 0.003 ms): dd/6330 write(fd: 2</dev/pts/0>, buf: 0x7fff22fc81f0, count: 25               ) = 25
> 
> Signed-off-by: David Ahern <dsahern@...il.com>
> ---
>  tools/lib/traceevent/event-parse.c | 11 ++++++++---
>  tools/lib/traceevent/event-parse.h |  1 +
>  tools/perf/builtin-trace.c         | 16 +++++++++++++---
>  3 files changed, 22 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
> index afe20ed9fac8..e8a29e730dfb 100644
> --- a/tools/lib/traceevent/event-parse.c
> +++ b/tools/lib/traceevent/event-parse.c
> @@ -6228,15 +6228,20 @@ void pevent_ref(struct pevent *pevent)
>  	pevent->ref_count++;
>  }
>  
> +void free_format_field(struct format_field *field)
> +{
> +	free(field->type);
> +	free(field->name);
> +	free(field);
> +}
> +
>  static void free_format_fields(struct format_field *field)
>  {
>  	struct format_field *next;
>  
>  	while (field) {
>  		next = field->next;
> -		free(field->type);
> -		free(field->name);
> -		free(field);
> +		free_format_field(field);
>  		field = next;
>  	}
>  }
> diff --git a/tools/lib/traceevent/event-parse.h b/tools/lib/traceevent/event-parse.h
> index 5b4efc062320..a548fac646f6 100644
> --- a/tools/lib/traceevent/event-parse.h
> +++ b/tools/lib/traceevent/event-parse.h
> @@ -619,6 +619,7 @@ enum pevent_errno pevent_parse_format(struct pevent *pevent,
>  				      const char *buf,
>  				      unsigned long size, const char *sys);
>  void pevent_free_format(struct event_format *event);
> +void free_format_field(struct format_field *field);
>  
>  void *pevent_get_field_raw(struct trace_seq *s, struct event_format *event,
>  			   const char *name, struct pevent_record *record,
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index dcd950ef2fd7..5caeefeda48a 100644


Up to here we should have a separate patch, one that I would like to
have an Acked-by: Rostedt, ok?

But then I don't think we need to do that, i.e. we can just have a
boolean we set at some point to tell that we need to skip the first
entry.

I'll try to cook up a patch for that.

- Arnaldo

> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c
> @@ -1442,14 +1442,24 @@ static int syscall__set_arg_fmts(struct syscall *sc)
>  	struct format_field *field;
>  	int idx = 0;
>  
> -	sc->arg_scnprintf = calloc(sc->tp_format->format.nr_fields - 1, sizeof(void *));
> +	field = sc->tp_format->format.fields;
> +	/* drop nr field - not relevant here; does not exist on older kernels */
> +	if (field && strcmp(field->name, "nr") == 0) {
> +		struct format_field *next = field->next;
> +
> +		free_format_field(field);
> +		sc->tp_format->format.fields = next;
> +		sc->tp_format->format.nr_fields--;
> +	}
> +
> +	sc->arg_scnprintf = calloc(sc->tp_format->format.nr_fields, sizeof(void *));
>  	if (sc->arg_scnprintf == NULL)
>  		return -1;
>  
>  	if (sc->fmt)
>  		sc->arg_parm = sc->fmt->arg_parm;
>  
> -	for (field = sc->tp_format->format.fields->next; field; field = field->next) {
> +	for (field = sc->tp_format->format.fields; field; field = field->next) {
>  		if (sc->fmt && sc->fmt->arg_scnprintf[idx])
>  			sc->arg_scnprintf[idx] = sc->fmt->arg_scnprintf[idx];
>  		else if (field->flags & FIELD_IS_POINTER)
> @@ -1547,7 +1557,7 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
>  			.thread = thread,
>  		};
>  
> -		for (field = sc->tp_format->format.fields->next; field;
> +		for (field = sc->tp_format->format.fields; field;
>  		     field = field->next, ++arg.idx, bit <<= 1) {
>  			if (arg.mask & bit)
>  				continue;
> -- 
> 2.2.1
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