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From:   Orson Zhai <orsonzhai@gmail.com>
Date:   Sat, 28 Mar 2020 14:17:43 +0800
Message-ID: <CA+H2tpE5Fe5zJKEUM7H9xT10+ZGKVmZ2Aa5D7j_eq7dvZyX5wA@mail.gmail.com>
Subject: Re: [RFC PATCH V2] dynamic_debug: Add config option of DYNAMIC_DEBUG_CORE
To:     Jason Baron <jbaron@akamai.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Shuah Khan <skhan@linuxfoundation.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Brendan Higgins <brendanhiggins@google.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ard Biesheuvel <ardb@kernel.org>,
        Andy Shevchenko <andy.shevchenko@gmail.com>,
        David Gow <davidgow@google.com>,
        Mark Rutland <mark.rutland@arm.com>, joe@perches.com,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Android Kernel Team <kernel-team@android.com>,
        Orson Zhai <orson.unisoc@gmail.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi Jason,

On Thu, Mar 26, 2020 at 1:13 AM Orson Zhai <orson.unisoc@gmail.com> wrote:
>
> Instead of enabling whole kernel with CONFIG_DYNAMIC_DEBUG, CONFIG_
> DYNAMIC_DEBUG_CORE will only make the basic function definition and
> exported symbols to be built without replacing pr_debug or dev_dbg
> to dynamic version unless DEBUG is defined for any desired modules

How do you think about this idea?
Optionally enable dynamic debug of modules by the DEBUG macro.

Best Regards,
-Orson

> together by users.
>
> This is useful for people who only want to enable dynamic debug for some
> specific kernel modules without worrying about whole kernel image size will
> be significantly increased and more memory consumption caused by CONFIG_
> DYNAMIC_DEBUG.
>
> Signed-off-by: Orson Zhai <orson.unisoc@gmail.com>
> ---
> Changes from V1:
> - Rewrite commit message for more generic usage.
> - Add combination use of CONFIG_DYNAMIC_DEBUG_CORE and DEBUG to enable
>   dynamic debug seperately.
> - Ignore empty _ddtable and return success when only the core is enabled.
> - Fix all typoes.
>
>  include/linux/dev_printk.h    |  6 ++++--
>  include/linux/dynamic_debug.h |  2 +-
>  include/linux/printk.h        | 12 ++++++++----
>  lib/Kconfig.debug             | 18 ++++++++++++++++++
>  lib/Makefile                  |  2 +-
>  lib/dynamic_debug.c           |  9 +++++++--
>  6 files changed, 39 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/dev_printk.h b/include/linux/dev_printk.h
> index 5aad06b..ed40030 100644
> --- a/include/linux/dev_printk.h
> +++ b/include/linux/dev_printk.h
> @@ -109,7 +109,8 @@ void _dev_info(const struct device *dev, const char *fmt, ...)
>  #define dev_info(dev, fmt, ...)                                                \
>         _dev_info(dev, dev_fmt(fmt), ##__VA_ARGS__)
>
> -#if defined(CONFIG_DYNAMIC_DEBUG)
> +#if defined(CONFIG_DYNAMIC_DEBUG) || \
> +       (defined(CONFIG_DYNAMIC_CORE) && defined(DEBUG))
>  #define dev_dbg(dev, fmt, ...)                                         \
>         dynamic_dev_dbg(dev, dev_fmt(fmt), ##__VA_ARGS__)
>  #elif defined(DEBUG)
> @@ -181,7 +182,8 @@ do {                                                                        \
>         dev_level_ratelimited(dev_notice, dev, fmt, ##__VA_ARGS__)
>  #define dev_info_ratelimited(dev, fmt, ...)                            \
>         dev_level_ratelimited(dev_info, dev, fmt, ##__VA_ARGS__)
> -#if defined(CONFIG_DYNAMIC_DEBUG)
> +#if defined(CONFIG_DYNAMIC_DEBUG) || \
> +       (defined(CONFIG_DYNAMIC_CORE) && defined(DEBUG))
>  /* descriptor check is first to prevent flooding with "callbacks suppressed" */
>  #define dev_dbg_ratelimited(dev, fmt, ...)                             \
>  do {                                                                   \
> 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/include/linux/printk.h b/include/linux/printk.h
> index 1e6108b..44d5378 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -292,7 +292,8 @@ extern int kptr_restrict;
>   * These can be used to print at the various log levels.
>   * All of these will print unconditionally, although note that pr_debug()
>   * and other debug macros are compiled out unless either DEBUG is defined
> - * or CONFIG_DYNAMIC_DEBUG is set.
> + * or CONFIG_DYNAMIC_DEBUG is set, or both CONFIG_DYNAMIC_DEBUG_CORE and
> + * DEBUG is defined.
>   */
>  #define pr_emerg(fmt, ...) \
>         printk(KERN_EMERG pr_fmt(fmt), ##__VA_ARGS__)
> @@ -327,7 +328,8 @@ extern int kptr_restrict;
>
>
>  /* If you are writing a driver, please use dev_dbg instead */
> -#if defined(CONFIG_DYNAMIC_DEBUG)
> +#if defined(CONFIG_DYNAMIC_DEBUG) || \
> +       (defined(CONFIG_DYNAMIC_CORE) && defined(DEBUG))
>  #include <linux/dynamic_debug.h>
>
>  /* dynamic_pr_debug() uses pr_fmt() internally so we don't need it here */
> @@ -453,7 +455,8 @@ extern int kptr_restrict;
>  #endif
>
>  /* If you are writing a driver, please use dev_dbg instead */
> -#if defined(CONFIG_DYNAMIC_DEBUG)
> +#if defined(CONFIG_DYNAMIC_DEBUG) || \
> +       (defined(CONFIG_DYNAMIC_CORE) && defined(DEBUG))
>  /* descriptor check is first to prevent flooding with "callbacks suppressed" */
>  #define pr_debug_ratelimited(fmt, ...)                                 \
>  do {                                                                   \
> @@ -500,7 +503,8 @@ static inline void print_hex_dump_bytes(const char *prefix_str, int prefix_type,
>
>  #endif
>
> -#if defined(CONFIG_DYNAMIC_DEBUG)
> +#if defined(CONFIG_DYNAMIC_DEBUG) || \
> +       (defined(CONFIG_DYNAMIC_CORE) && defined(DEBUG))
>  #define print_hex_dump_debug(prefix_str, prefix_type, rowsize, \
>                              groupsize, buf, len, ascii)        \
>         dynamic_hex_dump(prefix_str, prefix_type, rowsize,      \
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 69def4a..8381b19 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -99,6 +99,7 @@ config DYNAMIC_DEBUG
>         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 +165,23 @@ 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 as well.
> +
> +         This option can be selected with DEBUG together which could be
> +         defined for desired kernel modules to enable dynamic debug
> +         features instead for whole kernel. Especially being used in
> +         the case that kernel modules are built out of kernel tree to
> +         have dynamic debug capabilities without affecting the kernel
> +         base.
> +
>  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
> diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> index c604091..34f303a 100644
> --- a/lib/dynamic_debug.c
> +++ b/lib/dynamic_debug.c
> @@ -1014,8 +1014,13 @@ static int __init dynamic_debug_init(void)
>         int verbose_bytes = 0;
>
>         if (__start___verbose == __stop___verbose) {
> -               pr_warn("_ddebug table is empty in a CONFIG_DYNAMIC_DEBUG build\n");
> -               return 1;
> +               if (IS_ENABLED(CONFIG_DYNAMIC_DEBUG)) {
> +                       pr_warn("_ddebug table is empty in a CONFIG_DYNAMIC_DEBUG build\n");
> +                       return 1;
> +               }
> +               pr_info("Ignore empty _ddebug table in a core only build\n");
> +               ddebug_init_success = 1;
> +               return 0;
>         }
>         iter = __start___verbose;
>         modname = iter->modname;
> --
> 2.7.4
>