linux-kernel - [PATCH] Revert "dynamic_debug: Remove unnecessary _

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Date:   Mon, 11 May 2020 11:26:58 -0700
From:   Elliot Berman <eberman@...eaurora.org>
To:     Jason Baron <jbaron@...mai.com>, Joe Perches <joe@...ches.com>
Cc:     Elliot Berman <eberman@...eaurora.org>,
        Trilok Soni <tsoni@...eaurora.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] Revert "dynamic_debug: Remove unnecessary __used"

This reverts commit c0d2af637863940b1a4fb208224ca7acb905c39f.

Some compilers[1] may break dynamic_hex_dump by optimizing the
DYNAMIC_DEBUG_BRANCH check inside __dynamic_func_call_no_desc and completely
removing the dynamic debug metadata. Thus, there is no dynamic_debug control
site to enable or disable. The if condition is optimized away based on the
initial value of flags (i.e. if DEBUG macro is present).

[1]: This behavior is present on [aarch64-gnu-linux-gcc (Ubuntu/Linaro
5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609] and [Android Common Kernel
toolchain: "Android (6051079 based on r370808) clang version
10.0.1"] using arm64 default defconfig + DYNAMIC_DEBUG enabled.

Change-Id: I28e9b86088eee5d5ed2384fbcea2ac2e7337a559
Signed-off-by: Elliot Berman <eberman@...eaurora.org>
---
 include/linux/dynamic_debug.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index abcd5fd..7518db4f 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -79,7 +79,7 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 			 const char *fmt, ...);

 #define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt)		\
-	static struct _ddebug  __aligned(8)			\
+	static struct _ddebug __used __aligned(8)		\
 	__attribute__((section("__verbose"))) name = {		\
 		.modname = KBUILD_MODNAME,			\
 		.function = __func__,				\
-- 
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