linux-kernel - Re: [PATCH] trace-cmd: Don't SIGSEGV when event field format cannot be parsed.

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Date:	Thu, 22 Jul 2010 16:08:45 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] trace-cmd: Don't SIGSEGV when event field format
 cannot be parsed.

On Tue, 2010-07-13 at 11:44 -0700, David Daney wrote:
> >From the MIPS kernel we get things like:
> 
> print fmt: "page=%p pfn=%lu order=%d migratetype=%d", REC->page, ({ struct page *__pg = (REC->page); int __sec = page_to_section(__pg); (unsigned long)(__pg - __section_mem_map_addr(__nr_to_section(__sec))); }), REC->order, REC->migratetype
> 
> This cannot be parsed, leading to a NULL struct event_format* being
> passed to pevent_get_common_field_val, which produces a SIGSEGV.  It
> would be good to get a parsable format from the kernel, but to
> remediate the problem for legacy kernels, we can just return an error
> indicator in this case.  This allows some output from trace-cmd
> report, although perhaps with some missing data.  But this is better
> than crashing.
> 
> Signed-off-by: David Daney <ddaney@...iumnetworks.com>
> ---
>  parse-events.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/parse-events.c b/parse-events.c
> index 9d5a3fa..16fff12 100644
> --- a/parse-events.c
> +++ b/parse-events.c
> @@ -4481,6 +4481,9 @@ int pevent_get_common_field_val(struct trace_seq *s, struct event_format *event,
>  {

To be consistent, probably all the pevent_get_*field* should test for
null event.

Did you want to resend a patch that does that?

-- Steve

>  	struct format_field *field;
>  
> +	if (!event)
> +		return -1;
> +
>  	field = pevent_find_common_field(event, name);
>  
>  	return get_field_val(s, field, name, record, val, err);


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