linux-kernel - Re: [PATCH v6 10/21] tracing: probeevent: Return consumed bytes of dynamic area

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Date:   Mon, 2 Apr 2018 16:02:07 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-trace-users@...r.kernel.org, linux-kselftest@...r.kernel.org,
        shuah@...nel.org, Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [PATCH v6 10/21] tracing: probeevent: Return consumed bytes of
 dynamic area

On Sat, 17 Mar 2018 21:44:52 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> -static nokprobe_inline void
> -fetch_store_string(unsigned long addr, void *dest)
> +static nokprobe_inline int
> +fetch_store_string(unsigned long addr, void *dest, void *base)
>  {
> -	int maxlen = get_rloc_len(*(u32 *)dest);
> -	u8 *dst = get_rloc_data(dest);
> +	int maxlen = get_loc_len(*(u32 *)dest);
> +	u8 *dst = get_loc_data(dest, base);
>  	long ret;
>  
>  	if (!maxlen)
> -		return;
> +		return -ENOMEM;
>  
>  	/*
>  	 * Try to get string again, since the string can be changed while
> @@ -854,19 +851,19 @@ fetch_store_string(unsigned long addr, void *dest)
>  
>  	if (ret < 0) {	/* Failed to fetch string */
>  		dst[0] = '\0';
> -		*(u32 *)dest = make_data_rloc(0, get_rloc_offs(*(u32 *)dest));
> -	} else {
> -		*(u32 *)dest = make_data_rloc(ret, get_rloc_offs(*(u32 *)dest));
> +		ret = 0;

Why do you return 0 here and not the error value? You return -ENOMEM
above if maxlen is zero.

-- Steve

>  	}
> +	*(u32 *)dest = make_data_loc(ret, (void *)dst - base);
> +	return ret;
>  }