Re: [PATCH v2] rcu: define tracepoint strings only if CONFIG_TRACING is set

[Steven Rostedt]

On Fri, 11 Jul 2014 22:50:45 +0200
Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:

> Commit f7f7bac9cb1c ("rcu: Have the RCU tracepoints use the tracepoint_string
> infrastructure") unconditionally populates the __tracepoint_str input section,
> but this section is not assigned an output section if CONFIG_TRACING is not set.
> This results in the __tracepoint_str turning up in unexpected places, i.e.,
> after _edata.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: rostedt@xxxxxxxxxxx
> Cc: paulmck@xxxxxxxxxxxxxxxxxx
> ---
> v2:
> - s/DEFINE_TPS/DEFINE_RCU_TPS/
> 
>  kernel/rcu/tree.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index f1ba77363fbb..eec9f3d6f506 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -79,9 +79,16 @@ static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
>   * the tracing userspace tools to be able to decipher the string
>   * address to the matching string.
>   */
> +#ifdef CONFIG_TRACING
> +#define DEFINE_RCU_TPS(sname) \
> +static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
> +#else
> +#define DEFINE_RCU_TPS(sname)
> +#endif
> +
>  #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
>  static char sname##_varname[] = #sname; \
> -static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; \
> +DEFINE_RCU_TPS(sname) \
>  struct rcu_state sname##_state = { \
>  	.level = { &sname##_state.node[0] }, \
>  	.call = cr, \

Looking at this a bit deeper (actually looking at it in the context of
the code), we can make this even better.

#ifdef CONFIG_TRACING
# define DEFINE_RCU_TPS(sname) \
static char sname##_varname[] = #sname; \
static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
# define RCU_STATE_NAME(sname) sname##_varname;
#else
# define DEFINE_RCU_TPS(sname)
# define RCU_STATE_NAME(sname) __stringify(sname)
#endif

Then add:

	.name = RCU_STATE_NAME(sname), \


This will get rid of the sname##_varname variable as well.

-- Steve


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