[PATCH] Revert "dynamic_debug: Remove unnecessary __used"

[PATCH] Revert "dynamic_debug: Remove unnecessary __used"

[Elliot Berman]

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

Re: [PATCH] Revert "dynamic_debug: Remove unnecessary __used"

[Joe Perches]

On Mon, 2020-05-11 at 11:26 -0700, Elliot Berman wrote:
> 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>
> ---

Change-Id: probably isn't necessary.

Is there a separate mechanism possible to avoid bloating the
otherwise unused content?

>  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__,				\

Re: [PATCH] Revert "dynamic_debug: Remove unnecessary __used"

[Elliot Berman]

On 5/11/2020 11:54 AM, Joe Perches wrote> Change-Id: probably isn't necessary.

Thanks for the catch

> 
> Is there a separate mechanism possible to avoid bloating the
> otherwise unused content?

This struct is being used in lib/dynamic_debug.c but compiler doesn't know
about this usage when optimizing the struct/branch away.
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [PATCH] Revert "dynamic_debug: Remove unnecessary __used"

[Joe Perches]

On Mon, 2020-05-11 at 12:31 -0700, Elliot Berman wrote:
> On 5/11/2020 11:54 AM, Joe Perches wrote> Change-Id: probably isn't necessary.
> 
> Thanks for the catch
> 
> > Is there a separate mechanism possible to avoid bloating the
> > otherwise unused content?
> 
> This struct is being used in lib/dynamic_debug.c but compiler doesn't know
> about this usage when optimizing the struct/branch away.

I only remember that I removed __used awhile ago
because it _wasn't_ used in some paths.

Maybe that's changed, but I don't know.