tracing/synthetic: Fix order of struct trace_dynamic_info

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/[e-mail]/
Link: https://lore.kernel.org/linux-trace-kernel/[e-mail]

Cc: [e-mail]
Cc: Mark Rutland <[e-mail]>
Tested-by: Sven Schnelle <[e-mail]>
Acked-by: Masami Hiramatsu (Google) <[e-mail]>
Fixes: ddeea494a16f3 ("tracing/synthetic: Use union instead of casts")
Signed-off-by: Steven Rostedt (Google) <[e-mail]>

include/linux/trace_events.h

···
 /* 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