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From: Elliot Berman <eberman@codeaurora.org>
To: Jason Baron <jbaron@akamai.com>, Joe Perches <joe@perches.com>
Cc: Trilok Soni <tsoni@codeaurora.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH] Revert "dynamic_debug: Remove unnecessary __used"
Date: Mon, 11 May 2020 11:26:58 -0700	[thread overview]
Message-ID: <1589221618-21808-1-git-send-email-eberman@codeaurora.org> (raw)

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@codeaurora.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__,				\
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

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WARNING: multiple messages have this Message-ID (diff)
From: Elliot Berman <eberman@codeaurora.org>
To: Jason Baron <jbaron@akamai.com>, Joe Perches <joe@perches.com>
Cc: Elliot Berman <eberman@codeaurora.org>,
	Trilok Soni <tsoni@codeaurora.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH] Revert "dynamic_debug: Remove unnecessary __used"
Date: Mon, 11 May 2020 11:26:58 -0700	[thread overview]
Message-ID: <1589221618-21808-1-git-send-email-eberman@codeaurora.org> (raw)

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@codeaurora.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__,				\
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

             reply	other threads:[~2020-05-11 18:27 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-11 18:26 Elliot Berman [this message]
2020-05-11 18:26 ` [PATCH] Revert "dynamic_debug: Remove unnecessary __used" Elliot Berman
2020-05-11 18:54 ` Joe Perches
2020-05-11 18:54   ` Joe Perches
2020-05-11 19:31   ` Elliot Berman
2020-05-11 19:31     ` Elliot Berman
2020-05-11 19:56     ` Joe Perches
2020-05-11 19:56       ` Joe Perches

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