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

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Message-ID: <0a9453d94419991aa38d64b7a446eeba1f9c5a80.camel@perches.com>
Date:   Mon, 10 Oct 2022 19:35:38 -0700
From:   Joe Perches <joe@...ches.com>
To:     Zheng Yejian <zhengyejian1@...wei.com>, rostedt@...dmis.org,
        mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ftrace: Fix char print issue in print_ip_ins()

On Mon, 2022-10-10 at 19:15 +0000, Zheng Yejian wrote:
> 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
[]
> @@ -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)) {

Perhaps nicer would be to change the for loop below this from

	for (i = 0; i < MCOUNT_INSN_SIZE; i++)
		printk(KERN_CONT "%s%02x", i ? ":" : "", ins[i]);

to

	pr_cont("%*phC", MCOUNT_INSN_SIZE, ins);