linux-kernel - [PATCH 1/2] Rename .data.unlikely to .data..unlikely

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Message-ID: <20241106161445.189399-1-masahiroy@kernel.org>
Date: Thu,  7 Nov 2024 01:14:40 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: linux-kbuild@...r.kernel.org
Cc: Nicholas Piggin <npiggin@...il.com>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Boqun Feng <boqun.feng@...il.com>,
	Frederic Weisbecker <frederic@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	rcu@...r.kernel.org
Subject: [PATCH 1/2] Rename .data.unlikely to .data..unlikely

Commit 7ccaba5314ca ("consolidate WARN_...ONCE() static variables")
was intended to collect all .data.unlikely sections into one chunk.
However, this has not worked when CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
or CONFIG_LTO_CLANG is enabled, because .data.unlikely matches the
.data.[0-9a-zA-Z_]* pattern in the DATA_MAIN macro.

Commit cb87481ee89d ("kbuild: linker script do not match C names unless
LD_DEAD_CODE_DATA_ELIMINATION is configured") was introduced to suppress
the issue for the default CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=n case,
providing a minimal fix for stable backporting. We were aware this did
not address the issue for CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y. The
plan was to apply correct fixes and then revert cb87481ee89d. [1]

Seven years have passed since then, yet the #ifdef workaround remains in
place.

Using a ".." separator in the section name fixes the issue for
CONFIG_LD_DEAD_CODE_DATA_ELIMINATION and CONFIG_LTO_CLANG.

[1]: https://lore.kernel.org/linux-kbuild/CAK7LNASck6BfdLnESxXUeECYL26yUDm0cwRZuM4gmaWUkxjL5g@mail.gmail.com/

Fixes: cb87481ee89d ("kbuild: linker script do not match C names unless LD_DEAD_CODE_DATA_ELIMINATION is configured")
Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 include/asm-generic/vmlinux.lds.h | 2 +-
 include/linux/rcupdate.h          | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index c995474e4c64..3c9dc1fd094d 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -357,7 +357,7 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
 	*(.data..decrypted)						\
 	*(.ref.data)							\
 	*(.data..shared_aligned) /* percpu related */			\
-	*(.data.unlikely)						\
+	*(.data..unlikely)						\
 	__start_once = .;						\
 	*(.data.once)							\
 	__end_once = .;							\
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 58d84c59f3dd..48e5c03df1dd 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -401,7 +401,7 @@ static inline int debug_lockdep_rcu_enabled(void)
  */
 #define RCU_LOCKDEP_WARN(c, s)						\
 	do {								\
-		static bool __section(".data.unlikely") __warned;	\
+		static bool __section(".data..unlikely") __warned;	\
 		if (debug_lockdep_rcu_enabled() && (c) &&		\
 		    debug_lockdep_rcu_enabled() && !__warned) {		\
 			__warned = true;				\
-- 
2.43.0