On Fri, 8 Sep 2023 16:39:29 -0400
Steven Rostedt <rost...@goodmis.org> wrote:
> From: "Steven Rostedt (Google)" <rost...@goodmis.org>
>
> To make handling BIG and LITTLE endian better the offset/len of dynamic
> fields of the synthetic events was changed into a structure of:
>
> struct trace_dynamic_info {
> #ifdef CONFIG_CPU_BIG_ENDIAN
> u16 offset;
> u16 len;
> #else
> u16 len;
> u16 offset;
> #endif
> };
>
> to replace the manual changes of:
>
> data_offset = offset & 0xffff;
> data_offest = len << 16;
>
> But if you look closely, the above is:
>
> <len> << 16 | offset
>
> Which in little endian would be in memory:
>
> offset_lo offset_hi len_lo len_hi
>
> and in big endian:
>
> len_hi len_lo offset_hi offset_lo
>
> Which if broken into a structure would be:
>
> struct trace_dynamic_info {
> #ifdef CONFIG_CPU_BIG_ENDIAN
> u16 len;
> u16 offset;
> #else
> u16 offset;
> u16 len;
> #endif
> };
>
> Which is the opposite of what was defined.
>
> Fix this and just to be safe also add "__packed".
>
> Link: https://lore.kernel.org/all/20230908154417.5172e...@gandalf.local.home/
Good catch! I'm not sure why this worked. Maybe we don't have any testcase
for this feature?
Acked-by: Masami Hiramatsu (Google) <mhira...@kernel.org>
Thank you,
>
> Cc: sta...@vger.kernel.org
> Fixes: ddeea494a16f3 ("tracing/synthetic: Use union instead of casts")
> Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org>
> ---
>
> [ Resending to the correct mailing list this time :-p ]
>
> include/linux/trace_events.h | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 12f875e9e69a..21ae37e49319 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -62,13 +62,13 @@ void trace_event_printf(struct trace_iterator *iter,
> const char *fmt, ...);
> /* Used to find the offset and length of dynamic fields in trace events */
> struct trace_dynamic_info {
> #ifdef CONFIG_CPU_BIG_ENDIAN
> - u16 offset;
> u16 len;
> + u16 offset;
> #else
> - u16 len;
> u16 offset;
> + u16 len;
> #endif
> -};
> +} __packed;
>
> /*
> * The trace entry - the most basic unit of tracing. This is what
> --
> 2.40.1
>
--
Masami Hiramatsu (Google) <mhira...@kernel.org>
