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* [PATCH] tracing: Fix align of static buffer
@ 2020-11-25 22:56 Minchan Kim
  2020-11-26  5:52 ` Greg KH
       [not found] ` <>
  0 siblings, 2 replies; 5+ messages in thread
From: Minchan Kim @ 2020-11-25 22:56 UTC (permalink / raw)
  To: Steven Rostedt; +Cc: LKML, Minchan Kim, stable, Namhyung Kim

With 5.9 kernel on ARM64, I found ftrace_dump output was broken but
it had no problem with normal output "cat /sys/kernel/debug/tracing/trace".

With investigation, it seems coping the data into temporal buffer seems to
break the align binary printf expects if the static buffer is not aligned
with 4-byte. IIUC, get_arg in bstr_printf expects that args has already
right align to be decoded and seq_buf_bprintf says ``the arguments are saved
in a 32bit word array that is defined by the format string constraints``.
So if we don't keep the align under copy to temporal buffer, the output
will be broken by shifting some bytes.

This patch fixes it.

Cc: <>
Fixes: 8e99cf91b99bb ("tracing: Do not allocate buffer in trace_find_next_entry() in atomic")
Signed-off-by: Namhyung Kim <>
Signed-off-by: Minchan Kim <>
 kernel/trace/trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6a282bbc7e7f..01bfcc345d55 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3534,7 +3534,7 @@ __find_next_entry(struct trace_iterator *iter, int *ent_cpu,
-static char static_temp_buf[STATIC_TEMP_BUF_SIZE];
+static char static_temp_buf[STATIC_TEMP_BUF_SIZE] __aligned(4);
 /* Find the next real entry, without updating the iterator itself */
 struct trace_entry *trace_find_next_entry(struct trace_iterator *iter,

^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2020-11-26 18:06 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-11-25 22:56 [PATCH] tracing: Fix align of static buffer Minchan Kim
2020-11-26  5:52 ` Greg KH
2020-11-26  9:31   ` Namhyung Kim
     [not found] ` <>
2020-11-26 13:04   ` Youngmin Nam
2020-11-26 18:05     ` Minchan Kim

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