linux-kernel - [PATCH] tracing: move buffer in trace

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Message-ID: <20250821053917.23301-1-git@elijahs.space>
Date: Wed, 20 Aug 2025 22:39:07 -0700
From: Elijah Wright <git@...jahs.space>
To: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Cc: Elijah Wright <git@...jahs.space>
Subject: [PATCH] tracing: move buffer in trace_seq to end of struct

TRACE_SEQ_BUFFER_SIZE is dependent on the architecture for its size. on 64-bit
systems, it is 8148 bytes. forced 8-byte alignment in size_t and seq_buf means
that trace_seq is 8200 bytes on 64-bit systems. moving the buffer to the end
of the struct fixes the issue. there shouldn't be any side effects, i.e.
pointer arithmetic on trace_seq

Signed-off-by: Elijah Wright <git@...jahs.space>
---
 include/linux/trace_seq.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/trace_seq.h b/include/linux/trace_seq.h
index a93ed5ac3226..557780fe1c77 100644
--- a/include/linux/trace_seq.h
+++ b/include/linux/trace_seq.h
@@ -21,10 +21,10 @@
 	(sizeof(struct seq_buf) + sizeof(size_t) + sizeof(int)))
 
 struct trace_seq {
-	char			buffer[TRACE_SEQ_BUFFER_SIZE];
 	struct seq_buf		seq;
 	size_t			readpos;
 	int			full;
+	char                    buffer[TRACE_SEQ_BUFFER_SIZE];
 };
 
 static inline void
-- 
2.43.0