linux-kernel - Re: [PATCH 1/3] tracing: correctly expand len expressions from __dynamic

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Date:	Mon, 3 Mar 2014 14:51:10 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Filipe Brandenburger <filbranden@...gle.com>
Cc:	Li Zefan <lizefan@...wei.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] tracing: correctly expand len expressions from
 __dynamic_array macro

On Fri, 28 Feb 2014 21:32:16 -0800
Filipe Brandenburger <filbranden@...gle.com> wrote:

> This fixes expansion of the len argument in __dynamic_array macros.
> The previous code from commit 7d536cb3f would not fully evaluate the
> expression before multiplying its result by the size of the type.
> 
> This went unnoticed because the length stored in the high 16 bits of the
> offset (which is the one that was broken here) is only used by
> filter_pred_strloc which only acts on strings for which the size of the
> type is 1.
> 

Was this visible in any of the tracepoints? Should this be marked for
stable? It's been in the kernel for a long time (2009). Or is a new
tracepoint showing a problem?

-- Steve

> Signed-off-by: Filipe Brandenburger <filbranden@...gle.com>
> ---
>  include/trace/ftrace.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
> index 1a8b28d..82e8d89 100644
> --- a/include/trace/ftrace.h
> +++ b/include/trace/ftrace.h
> @@ -375,7 +375,7 @@ ftrace_define_fields_##call(struct ftrace_event_call *event_call)	\
>  #define __dynamic_array(type, item, len)				\
>  	__data_offsets->item = __data_size +				\
>  			       offsetof(typeof(*entry), __data);	\
> -	__data_offsets->item |= (len * sizeof(type)) << 16;		\
> +	__data_offsets->item |= ((len) * sizeof(type)) << 16;		\
>  	__data_size += (len) * sizeof(type);
>  
>  #undef __string

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