linux-kernel - [PATCH v2] ftrace: Fix char print issue in print_ip

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Message-ID: <20221011120352.1878494-1-zhengyejian1@huawei.com>
Date:   Tue, 11 Oct 2022 12:03:52 +0000
From:   Zheng Yejian <zhengyejian1@...wei.com>
To:     <rostedt@...dmis.org>, <mingo@...hat.com>,
        <linux-kernel@...r.kernel.org>
CC:     <joe@...ches.com>, <zhengyejian1@...wei.com>
Subject: [PATCH v2] ftrace: Fix char print issue in print_ip_ins()

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

But so many 'f's seem a little confusing, and that is because format
'%x' being used to print signed chars in array 'ins'. As suggested
by Joe, change to use format "%*phC" to print array '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()")
Suggested-by: Joe Perches <joe@...ches.com>
Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
---
 kernel/trace/ftrace.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

 Changes since v1:
   Use format "%*phC" to print array 'ins' as suggested by Joe.
   Link: https://lore.kernel.org/lkml/0a9453d94419991aa38d64b7a446eeba1f9c5a80.camel@perches.com/#t
   Usage of format "%*phC" can also be found in Documentation/core-api/printk-formats.rst "Raw buffer as a hex string"

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 447d2e2a8549..b838c717037a 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2016,7 +2016,6 @@ 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];
-	int i;
 
 	if (copy_from_kernel_nofault(ins, p, MCOUNT_INSN_SIZE)) {
 		printk(KERN_CONT "%s[FAULT] %px\n", fmt, p);
@@ -2024,9 +2023,7 @@ static void print_ip_ins(const char *fmt, const unsigned char *p)
 	}
 
 	printk(KERN_CONT "%s", fmt);
-
-	for (i = 0; i < MCOUNT_INSN_SIZE; i++)
-		printk(KERN_CONT "%s%02x", i ? ":" : "", ins[i]);
+	pr_cont("%*phC", MCOUNT_INSN_SIZE, ins);
 }
 
 enum ftrace_bug_type ftrace_bug_type;
-- 
2.25.1