linux-kernel - Re: [PATCH v2 04/44] trace/ring_buffer: handle 64bit aligned structs

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Message-ID: <1354929851.17101.105.camel@gandalf.local.home>
Date:	Fri, 07 Dec 2012 20:24:11 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	James Hogan <james.hogan@...tec.com>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v2 04/44] trace/ring_buffer: handle 64bit aligned structs

On Wed, 2012-12-05 at 16:08 +0000, James Hogan wrote:
> Some 32 bit architectures have 64 bit struct alignment (for example
> Meta which has 64 bit read/write instructions). These require 8 byte
> alignment of event data too, so use CONFIG_HAVE_64BIT_ALIGNED_STRUCT
> instead of CONFIG_64BIT to decide alignment, and align
> buffer_data_page::data accordingly.
> 
> Signed-off-by: James Hogan <james.hogan@...tec.com>

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> ---
>  kernel/trace/ring_buffer.c |    7 +++++--
>  1 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index b979426..c4dc029 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -177,7 +177,8 @@ void tracing_off_permanent(void)
>  #define RB_MAX_SMALL_DATA	(RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
>  #define RB_EVNT_MIN_SIZE	8U	/* two 32bit words */
>  
> -#if !defined(CONFIG_64BIT) || defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
> +#if !defined(CONFIG_HAVE_64BIT_ALIGNED_STRUCT) || \
> +	defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
>  # define RB_FORCE_8BYTE_ALIGNMENT	0
>  # define RB_ARCH_ALIGNMENT		RB_ALIGNMENT
>  #else
> @@ -185,6 +186,8 @@ void tracing_off_permanent(void)
>  # define RB_ARCH_ALIGNMENT		8U
>  #endif
>  
> +#define RB_ALIGN_DATA		__aligned(RB_ARCH_ALIGNMENT)
> +
>  /* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
>  #define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
>  
> @@ -333,7 +336,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data);
>  struct buffer_data_page {
>  	u64		 time_stamp;	/* page time stamp */
>  	local_t		 commit;	/* write committed index */
> -	unsigned char	 data[];	/* data of buffer page */
> +	unsigned char	 data[] RB_ALIGN_DATA;	/* data of buffer page */
>  };
>  
>  /*


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