linux-kernel - [PATCH] ftrace: Fix char print issue in print_ip

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Date:   Mon, 10 Oct 2022 19:15:24 +0000
From:   Zheng Yejian <zhengyejian1@...wei.com>
To:     <rostedt@...dmis.org>, <mingo@...hat.com>,
        <linux-kernel@...r.kernel.org>
CC:     <zhengyejian1@...wei.com>
Subject: [PATCH] ftrace: Fix char print issue in print_ip_ins()

When ftrace bug happened, following log shows every byte data in
problem ip address:
  actual:   ffffffe8:6b:ffffffd9:01:21

However that seems a little confusing, and it is because format
'%x' being used to print signed chars in print_ip_ins().

After this patch, the log is like:
  actual:   e8:6b:d9:01:21

Fixes: 6c14133d2d3f ("ftrace: Do not blindly read the ip address in ftrace_bug()")
Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
---
 kernel/trace/ftrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 439e2ab6905e..251ba30c871d 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2015,7 +2015,7 @@ static int ftrace_hash_ipmodify_update(struct ftrace_ops *ops,
 
 static void print_ip_ins(const char *fmt, const unsigned char *p)
 {
-	char ins[MCOUNT_INSN_SIZE];
+	unsigned char ins[MCOUNT_INSN_SIZE];
 	int i;
 
 	if (copy_from_kernel_nofault(ins, p, MCOUNT_INSN_SIZE)) {
-- 
2.25.1