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

[Qian-Yu Lin]

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.

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.

Signed-off-by: Qian-Yu Lin <tiffany019230@xxxxxxxxx>
---
 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>
 #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			\
-- 
2.25.1