linux-kernel - Re: [PATCH] samples: Use KSYM_NAME

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Message-Id: <20220608011739.4331f96f3354e05f23c26dde@kernel.org>
Date:   Wed, 8 Jun 2022 01:17:39 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] samples: Use KSYM_NAME_LEN for fprobe and kprobes

On Tue,  7 Jun 2022 17:35:36 +0800
Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:

> It is better and enough to use KSYM_NAME_LEN for fprobe and kprobes
> in samples, no need to define and use the other values.
> 

This is good for kprobe and kretprobe examples because it will get
a single symbol name, but not good for the fprobe. It can take
several comma separated symbols.

-----
static int __init fprobe_init(void)
{
...
        /* Comma separated symbols */
        symbuf = kstrdup(symbol, GFP_KERNEL);
        if (!symbuf)
                return -ENOMEM;
        p = symbuf;
        count = 1;
        while ((p = strchr(++p, ',')) != NULL)
                count++;

        pr_info("%d symbols found\n", count);
-----

Can you drop the fprobe_example.c part?

Thank you,

> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>  samples/fprobe/fprobe_example.c     | 9 ++++-----
>  samples/kprobes/kprobe_example.c    | 5 ++---
>  samples/kprobes/kretprobe_example.c | 5 ++---
>  3 files changed, 8 insertions(+), 11 deletions(-)
> 
> diff --git a/samples/fprobe/fprobe_example.c b/samples/fprobe/fprobe_example.c
> index 24d3cf1..1ed1a69 100644
> --- a/samples/fprobe/fprobe_example.c
> +++ b/samples/fprobe/fprobe_example.c
> @@ -19,13 +19,12 @@
>  #include <linux/slab.h>
>  
>  #define BACKTRACE_DEPTH 16
> -#define MAX_SYMBOL_LEN 4096
>  struct fprobe sample_probe;
>  
> -static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
> -module_param_string(symbol, symbol, sizeof(symbol), 0644);
> -static char nosymbol[MAX_SYMBOL_LEN] = "";
> -module_param_string(nosymbol, nosymbol, sizeof(nosymbol), 0644);
> +static char symbol[KSYM_NAME_LEN] = "kernel_clone";
> +module_param_string(symbol, symbol, KSYM_NAME_LEN, 0644);
> +static char nosymbol[KSYM_NAME_LEN] = "";
> +module_param_string(nosymbol, nosymbol, KSYM_NAME_LEN, 0644);
>  static bool stackdump = true;
>  module_param(stackdump, bool, 0644);
>  
> diff --git a/samples/kprobes/kprobe_example.c b/samples/kprobes/kprobe_example.c
> index f991a66..fd346f5 100644
> --- a/samples/kprobes/kprobe_example.c
> +++ b/samples/kprobes/kprobe_example.c
> @@ -16,9 +16,8 @@
>  #include <linux/module.h>
>  #include <linux/kprobes.h>
>  
> -#define MAX_SYMBOL_LEN	64
> -static char symbol[MAX_SYMBOL_LEN] = "kernel_clone";
> -module_param_string(symbol, symbol, sizeof(symbol), 0644);
> +static char symbol[KSYM_NAME_LEN] = "kernel_clone";
> +module_param_string(symbol, symbol, KSYM_NAME_LEN, 0644);
>  
>  /* For each probe you need to allocate a kprobe structure */
>  static struct kprobe kp = {
> diff --git a/samples/kprobes/kretprobe_example.c b/samples/kprobes/kretprobe_example.c
> index 228321e..cbf1654 100644
> --- a/samples/kprobes/kretprobe_example.c
> +++ b/samples/kprobes/kretprobe_example.c
> @@ -23,11 +23,10 @@
>  #include <linux/module.h>
>  #include <linux/kprobes.h>
>  #include <linux/ktime.h>
> -#include <linux/limits.h>
>  #include <linux/sched.h>
>  
> -static char func_name[NAME_MAX] = "kernel_clone";
> -module_param_string(func, func_name, NAME_MAX, S_IRUGO);
> +static char func_name[KSYM_NAME_LEN] = "kernel_clone";
> +module_param_string(func, func_name, KSYM_NAME_LEN, 0644);
>  MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
>  			" function's execution time");
>  
> -- 
> 2.1.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>