Re: [PATCH] trace_printk: replace _______STR with __UNIQUE_ID(STR)

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 30 Apr 2026 00:57:07 +0800
Qian-Yu Lin <tiffany019230@gmail.com> wrote:

> The macro trace_printk() uses a hardcoded identifier _______STR
> within a statement expression, which can lead to variable name
> shadowing if a caller happens to use the same name in its scope.

Has this ever been a problem?

> 
> Following the pattern in commit 24ba53017e18 ("rcu: Replace ________p1
> and _________p1 with __UNIQUE_ID(rcu)") and commit 589a9785ee3a
>  ("min/max: remove sparse warnings when they're nested"), replace the
>  hardcoded identifier with __UNIQUE_ID(STR).
> 
> Since __UNIQUE_ID() must be expanded once to remain consistent across
> declaration and sizeof() within the statement expression, introduce a
> nested helper macro ___trace_printk.

Hmm, so we are replacing one name with underscores with another name
with underscores?

> 
> Signed-off-by: Qian-Yu Lin <tiffany019230@gmail.com>
> ---
>  include/linux/trace_printk.h | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/trace_printk.h b/include/linux/trace_printk.h
> index 2670ec7f4262..060eccb40838 100644
> --- a/include/linux/trace_printk.h
> +++ b/include/linux/trace_printk.h
> @@ -2,6 +2,7 @@
>  #ifndef _LINUX_TRACE_PRINTK_H
>  #define _LINUX_TRACE_PRINTK_H
>  
> +#include <linux/compiler.h>

People are already saying that trace_printk.h slows down the compile.
Does this add any overhead to the compile?

-- Steve


>  #include <linux/compiler_attributes.h>
>  #include <linux/instruction_pointer.h>
>  #include <linux/stddef.h>
> @@ -84,15 +85,18 @@ do {									\
>   * let gcc optimize the rest.
>   */
>  
> -#define trace_printk(fmt, ...)				\
> +#define ___trace_printk(fmt, str, ...)				\
>  do {							\
> -	char _______STR[] = __stringify((__VA_ARGS__));	\
> -	if (sizeof(_______STR) > 3)			\
> +	char str[] = __stringify((__VA_ARGS__));	\
> +	if (sizeof(str) > 3)			\
>  		do_trace_printk(fmt, ##__VA_ARGS__);	\
>  	else						\
>  		trace_puts(fmt);			\
>  } while (0)
>  
> +#define trace_printk(fmt, ...) \
> +	___trace_printk(fmt, __UNIQUE_ID(str), ##__VA_ARGS__)
> +
>  #define do_trace_printk(fmt, args...)					\
>  do {									\
>  	static const char *trace_printk_fmt __used			\