linux-kernel - Re: [PATCH 2/7] tracing: Change strlen to sizeof for hist trigger static strings

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Date:   Wed, 19 Dec 2018 12:22:38 -0800
From:   Joe Perches <joe@...ches.com>
To:     Tom Zanussi <zanussi@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     tglx@...utronix.de, mhiramat@...nel.org, namhyung@...nel.org,
        vedang.patel@...el.com, bigeasy@...utronix.de,
        joel@...lfernandes.org, mathieu.desnoyers@...icios.com,
        julia@...com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org
Subject: Re: [PATCH 2/7] tracing: Change strlen to sizeof for hist trigger
 static strings

On Wed, 2018-12-19 at 14:16 -0600, Tom Zanussi wrote:
> 
> How's this?
> 
> [PATCH] tracing: Introduce and use strcmp_const() for hist triggers
> 
> Provide a new strcmp_const() macro and make use of it instead of the
> longer and more error-prone strncmp(str, "str", sizeof("str") - 1).
[]
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
[]
> @@ -22,6 +22,9 @@
>  
>  #define STR_VAR_LEN_MAX		32 /* must be multiple of sizeof(u64) */
>  
> +#define strcmp_const(str, str_const) \
> +	strncmp(str, str_const, sizeof(str_const) - 1)

Not good as it's too easy to pass a pointer as str_const
and sizeof(pointer) - 1 isn't likely the string length.