Re: [RESEND][PATCH] tracing/synthetic: Fix order of struct trace_dynamic_info
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Date: 2023-09-11 00:26:20
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On Fri, 8 Sep 2023 16:39:29 -0400 Steven Rostedt [off-list ref] wrote:
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/ (local)Good catch! I'm not sure why this worked. Maybe we don't have any testcase for this feature? Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Thank you,
quoted hunk ↗ jump to hunk
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(-)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) [off-list ref]