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

[Qian-Yu Lin <tiffany019230@gmail.com>]

On Fri, May 01, 2026 at 11:19:39AM -0400, Steven Rostedt wrote:
> On Fri, 1 May 2026 22:40:17 +0800
> Qian-Yu Lin <tiffany019230@gmail.com> wrote:
> 
> > I propose using a compound literal in v2, which eliminates the local
> > variable entirely and requires no extra include:
> > 
> > #define trace_printk(fmt, ...)                          \
> > do {                                                    \
> >     if (sizeof((char[])                             \
> >         {__stringify((__VA_ARGS__))}) > 3)      \
> >         do_trace_printk(fmt, ##__VA_ARGS__);    \
> >     else                                            \
> >         trace_puts(fmt);                        \
> > } while (0)
> > 
> > This fully eliminates the shadowing risk without any compile overhead.
> 
> Have you tested to make sure a string with no arguments still produces the
> trace_puts() and one that has arguments calls do_trace_printk()?
> 
> I'm fine with that one if it still works.
> 
> -- Steve

Yes, I verified it with the preprocessor output. I created a minimal
test file:

// kernel/trace/test_trace_printk.c
#include <linux/trace_printk.h>

void test(void) {
    trace_printk("no args\n");
    trace_printk("with arg %d\n", 42);
}

Then ran make kernel/trace/test_trace_printk.i.

The no-args case has sizeof((char[]){"()"}) which is 3, so 3 > 3 is
false and it falls through to trace_bputs/trace_puts.

The args case has sizeof((char[]){"(42)"}) which is 5, so 5 > 3 is
true and it goes to trace_bprintk/trace_printk with the argument
42 correctly passed through.

Qian-Yu