linux-kernel - Re: [PATCH v3 15/18] tracing: probeevent: Add array type support

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Message-ID: <20180226014532.GB1972@sejong>
Date:   Mon, 26 Feb 2018 10:45:32 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        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, kernel-team@....com
Subject: Re: [PATCH v3 15/18] tracing: probeevent: Add array type support

On Sat, Feb 24, 2018 at 02:35:40PM +0900, Masami Hiramatsu wrote:
> Add array type support for probe events.
> This allows user to get arraied types from memory address.
> The array type syntax is
> 
> 	TYPE[N]
> 
> Where TYPE is one of types (u8/16/32/64,s8/16/32/64,
> x8/16/32/64, symbol, string) and N is a fixed value less
> than 64.
> 
> The string array type is a bit different from other types. For
> other base types, <base-type>[1] is equal to <base-type>
> (e.g. +0(%di):x32[1] is same as +0(%di):x32.) But string[1] is not
> equal to string. The string type itself represents "char array",
> but string array type represents "char * array". So, for example,
> +0(%di):string[1] is equal to +0(+0(%di)):string.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  Changes in v2:
>   - Add array description in README file
>   - Fix to init s3 code out of loop.
>   - Fix to proceed code when the last code is OP_ARRAY.
>   - Add string array type and bitfield array type.
> ---

[SNIP]
> @@ -546,11 +610,16 @@ int traceprobe_define_arg_fields(struct trace_event_call *event_call,
>  	/* Set argument names as fields */
>  	for (i = 0; i < tp->nr_args; i++) {
>  		struct probe_arg *parg = &tp->args[i];
> -
> -		ret = trace_define_field(event_call, parg->type->fmttype,
> -					 parg->name,
> +		const char *fmt = parg->type->fmttype;
> +		int size = parg->type->size;
> +
> +		if (parg->fmt)
> +			fmt = parg->fmt;
> +		if (parg->count)
> +			size *= parg->count;
> +		ret = trace_define_field(event_call, fmt, parg->name,
>  					 offset + parg->offset,
> -					 parg->type->size,
> +					 parg->type->size * parg->count,

It should use the 'size' variable, otherwise scalar types will have 0 size.

Thanks,
Namhyung


>  					 parg->type->is_signed,
>  					 FILTER_OTHER);