linux-kernel - Re: [PATCH v3 1/3] tracing: Change STR_VAR_MAX

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Message-ID: <20201002154417.320ad78b@gandalf.local.home>
Date:   Fri, 2 Oct 2020 15:44:17 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Tom Zanussi <zanussi@...nel.org>
Cc:     axelrasmussen@...gle.com, mhiramat@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] tracing: Change STR_VAR_MAX_LEN

On Thu,  1 Oct 2020 16:46:44 -0500
Tom Zanussi <zanussi@...nel.org> wrote:

> 32 is too small for this value, and anyway it makes more sense to use
> MAX_FILTER_STR_VAL, as this is also the value used for variable-length
> __strings.
> 
> Tested-by: Axel Rasmussen <axelrasmussen@...gle.com>
> Signed-off-by: Tom Zanussi <zanussi@...nel.org>
> ---
>  kernel/trace/trace_synth.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_synth.h b/kernel/trace/trace_synth.h
> index ac35c45207c4..5166705d1556 100644
> --- a/kernel/trace/trace_synth.h
> +++ b/kernel/trace/trace_synth.h
> @@ -7,7 +7,7 @@
>  #define SYNTH_SYSTEM		"synthetic"
>  #define SYNTH_FIELDS_MAX	32
>  
> -#define STR_VAR_LEN_MAX		32 /* must be multiple of sizeof(u64) */
> +#define STR_VAR_LEN_MAX		MAX_FILTER_STR_VAL /* must be multiple of sizeof(u64) */

Hmm, this requirement is now passed to MAX_FILTER_STR_VAL, but there's no
mention of it there. I guess we should have a

	BUILD_BUG_ON(STR_VAR_LEN_MAX & (sizeof(u64) - 1));

in C code somewhere.

-- Steve


>  
>  struct synth_field {
>  	char *type;