linux-kernel - Re: [RFC PATCH] dynamic_debug: Add config option of DYNAMIC_DEBUG

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Message-ID: <51568376-da8b-3265-ddb3-6ddba74207dc@akamai.com>
Date:   Wed, 18 Mar 2020 17:18:43 -0400
From:   Jason Baron <jbaron@...mai.com>
To:     Orson Zhai <orson.unisoc@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Changbin Du <changbin.du@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ardb@...nel.org>,
        Gary Hook <Gary.Hook@....com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        David Gow <davidgow@...gle.com>,
        Mark Rutland <mark.rutland@....com>
Cc:     orsonzhai@...il.com, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [RFC PATCH] dynamic_debug: Add config option of
 DYNAMIC_DEBUG_CORE



On 3/18/20 3:03 PM, Orson Zhai wrote:
> There is the requirement from new Android that kernel image (GKI) and
> kernel modules are supposed to be built at differnet places. Some people
> want to enable dynamic debug for kernel modules only but not for kernel
> image itself with the consideration of binary size increased or more
> memory being used.
> 
> By this patch, dynamic debug is divided into core part (the defination of
> functions) and macro replacement part. We can only have the core part to
> be built-in and do not have to activate the debug output from kenrel image.
> 
> Signed-off-by: Orson Zhai <orson.unisoc@...il.com>

Hi Orson,

I think this is a nice feature. Is the idea then that driver can do
something like:

#if defined(CONFIG_DRIVER_FOO_DEBUG)
#define driver_foo_debug(fmt, ...) \
        dynamic_pr_debug(fmt, ##__VA_ARGS__)
#else
	no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
#enif

And then the Kconfig:

config DYNAMIC_DRIVER_FOO_DEBUG
	bool "Enable dynamic driver foo printk() support"
	select DYNAMIC_DEBUG_CORE


Or did you have something else in mind? Do you have an example
code for the drivers that you mention?

Thanks,

-Jason


> ---
>  include/linux/dynamic_debug.h |  2 +-
>  lib/Kconfig.debug             | 18 ++++++++++++++++--
>  lib/Makefile                  |  2 +-
>  3 files changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
> index 4cf02ec..abcd5fd 100644
> --- a/include/linux/dynamic_debug.h
> +++ b/include/linux/dynamic_debug.h
> @@ -48,7 +48,7 @@ struct _ddebug {
>  
>  
>  
> -#if defined(CONFIG_DYNAMIC_DEBUG)
> +#if defined(CONFIG_DYNAMIC_DEBUG_CORE)
>  int ddebug_add_module(struct _ddebug *tab, unsigned int n,
>  				const char *modname);
>  extern int ddebug_remove_module(const char *mod_name);
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 69def4a..78a7256 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -97,8 +97,7 @@ config BOOT_PRINTK_DELAY
>  config DYNAMIC_DEBUG
>  	bool "Enable dynamic printk() support"
>  	default n
> -	depends on PRINTK
> -	depends on DEBUG_FS
> +	select DYNAMIC_DEBUG_CORE
>  	help
>  
>  	  Compiles debug level messages into the kernel, which would not
> @@ -164,6 +163,21 @@ config DYNAMIC_DEBUG
>  	  See Documentation/admin-guide/dynamic-debug-howto.rst for additional
>  	  information.
>  
> +config DYNAMIC_DEBUG_CORE
> +	bool "Enable core functions of dynamic debug support"
> +	depends on PRINTK
> +	depends on DEBUG_FS
> +	help
> +	  Enable this option to build ddebug_* and __dynamic_* routines
> +	  into kernel. If you want enable whole dynamic debug features,
> +	  select CONFIG_DYNAMIC_DEBUG directly and this option will be
> +	  automatically selected.
> +
> +	  This option is selected when you want to enable dynamic debug
> +	  for kernel modules only but not for the kernel base. Especailly
> +	  in the case that kernel modules are built out of the place where
> +	  kernel base is built.
> +
>  config SYMBOLIC_ERRNAME
>  	bool "Support symbolic error names in printf"
>  	default y if PRINTK
> diff --git a/lib/Makefile b/lib/Makefile
> index 611872c..2096d83 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -183,7 +183,7 @@ lib-$(CONFIG_GENERIC_BUG) += bug.o
>  
>  obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o
>  
> -obj-$(CONFIG_DYNAMIC_DEBUG) += dynamic_debug.o
> +obj-$(CONFIG_DYNAMIC_DEBUG_CORE) += dynamic_debug.o
>  obj-$(CONFIG_SYMBOLIC_ERRNAME) += errname.o
>  
>  obj-$(CONFIG_NLATTR) += nlattr.o
>