On Thu, 30 Apr 2026 00:57:07 +0800
Qian-Yu Lin <[email protected]> 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 <[email protected]>
> ---
> 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 \
