[RESEND] tracing/synthetic: Fix order of struct trace_dynamic_info
Commit Message
From: "Steven Rostedt (Google)" <rostedt@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/20230908154417.5172e343@gandalf.local.home/
Cc: stable@vger.kernel.org
Fixes: ddeea494a16f3 ("tracing/synthetic: Use union instead of casts")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
[ Resending to the correct mailing list this time :-p ]
include/linux/trace_events.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
Comments
On Mon, 11 Sep 2023 09:26:12 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:
> > Fix this and just to be safe also add "__packed".
> >
> > Link: https://lore.kernel.org/all/20230908154417.5172e343@gandalf.local.home/
>
> Good catch! I'm not sure why this worked. Maybe we don't have any testcase
> for this feature?
We have a test case, it was broken by a change in the README :-p
I noticed issues with it, and then looked at the tests, fixed the test and
it failed. Before that, it was just reporting "unsupported", which is why I
included that fix with this queue.
https://lore.kernel.org/linux-trace-kernel/20230614091046.2178539-1-naveen@kernel.org/
>
> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Thanks!
-- Steve
@@ -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