[PATCH 1/3] kernel: Add a new config option to remove command line parsing

[PATCH 1/3] kernel: Add a new config option to remove command line parsing

[Iulia Manda]

This patch introduces CONFIG_CMDLINE_PARSE option which conditionally compiles
the support for parsing kernel command line arguments. The corresponding
functions that actually do the parsing will be compiled out. 

This is used when no parameters will be specified neither at compile time nor at
boot time.

Bloat-o-meter output (compared to the preivous version in which builtin cmdline
was also set to 'Y'):

add/remove: 0/8 grow/shrink: 0/6 up/down: 0/-3669 (-3669)
function                                     old     new   delta
load_module                                 5571    5563      -8
parse_early_param                             54      44     -10
parse_early_options                           33       5     -28
initcall_level_names                          32       -     -32
kernel_init_freeable                         413     360     -53
unknown_module_param_cb                       60       -     -60
setup_arch                                  3041    2972     -69
set_init_arg                                  73       -     -73
repair_env_string                             81       -     -81
start_kernel                                 857     759     -98
do_early_param                               117       -    -117
unknown_bootoption                           366       -    -366
parse_args                                   626       -    -626
builtin_cmdline                             2048       -   -2048

Signed-off-by: Iulia Manda <iulia.manda21@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 arch/x86/Kconfig            | 15 +++++++++++++++
 include/linux/moduleparam.h | 14 ++++++++++++++
 kernel/params.c             |  2 ++
 3 files changed, 31 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c2fb8a8..f1e02ea 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2003,8 +2003,23 @@ config COMPAT_VDSO
 	  If unsure, say N: if you are compiling your own kernel, you
 	  are unlikely to be using a buggy version of glibc.
 
+config CMDLINE_PARSE
+	bool "Enable support for command line parsing"
+	default y
+	---help---
+	  With this option set to 'Y', kernel parameters, both the ones
+	  passed at boot time and at compile time are parsed.
+
+	  If you say no here, all the kernel parameters' values will be set
+	  to their defaults at compile time, in order to make constant
+	  folding possible.
+
+	  Systems with no space constraints should leave this option set to
+	  'Y'.
+
 config CMDLINE_BOOL
 	bool "Built-in kernel command line"
+	depends on CMDLINE_PARSE
 	---help---
 	  Allow for specifying boot arguments to the kernel at
 	  build time.  On some systems (e.g. embedded ones), it is
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 1c9effa..f97397c 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -350,6 +350,7 @@ extern bool parameq(const char *name1, const char *name2);
  */
 extern bool parameqn(const char *name1, const char *name2, size_t n);
 
+#ifdef CONFIG_CMDLINE_PARSE
 /* Called on module insert or kernel boot */
 extern char *parse_args(const char *name,
 		      char *args,
@@ -359,6 +360,19 @@ extern char *parse_args(const char *name,
 		      s16 level_max,
 		      int (*unknown)(char *param, char *val,
 			      const char *doing));
+#else
+static inline char *parse_args(const char *name,
+		      char *args,
+		      const struct kernel_param *params,
+		      unsigned num,
+		      s16 level_min,
+		      s16 level_max,
+		      int (*unknown)(char *param, char *val,
+			      const char *doing))
+{
+        return NULL;
+}
+#endif
 
 /* Called by module remove. */
 #ifdef CONFIG_SYSFS
diff --git a/kernel/params.c b/kernel/params.c
index 728e05b..d3bfe47 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -93,6 +93,7 @@ static void param_check_unsafe(const struct kernel_param *kp)
 	}
 }
 
+#ifdef CONFIG_CMDLINE_PARSE
 static int parse_one(char *param,
 		     char *val,
 		     const char *doing,
@@ -239,6 +240,7 @@ char *parse_args(const char *doing,
 	/* All parsed OK. */
 	return NULL;
 }
+#endif
 
 /* Lazy bastard, eh? */
 #define STANDARD_PARAM_DEF(name, type, format, strtolfn)      		\
-- 
1.9.1

[PATCH 2/3] linux: Add macros that define and declare a core_param variable

[Iulia Manda]

This patch introduces two macros for kernel command line arguments subsequently
defined as core parameters:
* DECLARE_CORE_PARAM - declares an extern variable in case CMDLINE_PARSE is
set. In the other case it will make the variable a static constant asigned with
a default value to enable constant folding;
* DEFINE_CORE_PARAM - defines a core_param variable if CMDLINE_PARSE is set. In
the other case it leaves the definition to be handled by DECLARE_CORE_PARAM
macro.

Introducing a new header file for the declaration of kernel parameters seemed
to be the best option, because it solves the circular includes problem. Any
other proposal that would be fit for this case is welcomed.

Signed-off-by: Iulia Manda <iulia.manda21@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 include/linux/moduleparam.h |  9 +++++++++
 include/linux/params.h      | 12 ++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 include/linux/params.h

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index f97397c..17efa97 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -310,6 +310,15 @@ static inline void __kernel_param_unlock(void)
 #define core_param(name, var, type, perm)				\
 	param_check_##type(name, &(var));				\
 	__module_param_call("", name, &param_ops_##type, &var, perm, -1, 0)
+
+#ifdef CONFIG_CMDLINE_PARSE
+#define DEFINE_CORE_PARAM(name, var, val, type, perm)			\
+        type var = val;                                                 \
+        core_param(name, var, type, perm)
+#else
+#define DEFINE_CORE_PARAM(name, var, val, type, perm)
+#endif
+
 #endif /* !MODULE */
 
 /**
diff --git a/include/linux/params.h b/include/linux/params.h
new file mode 100644
index 0000000..c1ee6ff
--- /dev/null
+++ b/include/linux/params.h
@@ -0,0 +1,12 @@
+#ifndef _LINUX_PARAMS_H
+#define _LINUX_PARAMS_H
+
+#ifdef CONFIG_CMDLINE_PARSE
+#define DECLARE_CORE_PARAM(var, val, type)                              \
+        extern type var
+#else
+#define DECLARE_CORE_PARAM(var, val, type)                              \
+        static const type var = val
+#endif
+
+#endif /* _LINUX_PARAMS_H */
-- 
1.9.1

[PATCH 3/3] init: Set initcall_debug to a default value

[Iulia Manda]

Test the previously implemented macros on initcall_debug parameter, after
setting CONFIG_CMDLINE_PARSE to 'n'.

This change is a first example for how knowing the values of kernel parameters
at build time can allow GCC constant folding and result in an actually
relevant decrease in size. Other types of parameters also need to be handled.
Also, at the moment this would only work with default values. For being able
to change those defaults and still know their values at compile time, a
pre-compiled stand-alone parser should be run on those variables. This will be
discussed in a following patch.

The variable corresponding to initcall_debug kernel parameter is set by default
to false. Even though DEFINE_CORE_PARAM resumes to nothing when
CONFIG_CMDLINE_PARSE is not set, we need to use it in main.c so that it is
still defined when this option is 'y'.

Bloat-o-meter output:

add/remove: 0/3 grow/shrink: 0/9 up/down: 0/-385 (-385)
function                                     old     new   delta
initcall_debug                                 1       -      -1
pm_init                                      105     100      -5
__param_str_initcall_debug                    15       -     -15
__param_initcall_debug                        16       -     -16
syscore_suspend                              247     224     -23
syscore_resume                               175     152     -23
syscore_shutdown                              80      55     -25
pci_fixup_device                             235     198     -37
async_synchronize_cookie_domain              162     116     -46
async_run_entry_fn                           178     127     -51
device_shutdown                              256     204     -52
do_one_initcall                              339     248     -91

Signed-off-by: Iulia Manda <iulia.manda21@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 include/linux/init.h | 3 ++-
 init/main.c          | 3 +--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/init.h b/include/linux/init.h
index 2df8e8d..d53f28d 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -3,6 +3,7 @@
 
 #include <linux/compiler.h>
 #include <linux/types.h>
+#include <linux/params.h>
 
 /* These macros are used to mark some functions or 
  * initialized data (doesn't apply to uninitialized data)
@@ -155,7 +156,7 @@ int __init init_rootfs(void);
 
 extern void (*late_time_init)(void);
 
-extern bool initcall_debug;
+DECLARE_CORE_PARAM(initcall_debug, false, bool);
 
 #endif
   
diff --git a/init/main.c b/init/main.c
index 6f0f1c5f..85e9001 100644
--- a/init/main.c
+++ b/init/main.c
@@ -685,8 +685,7 @@ static void __init do_ctors(void)
 #endif
 }
 
-bool initcall_debug;
-core_param(initcall_debug, initcall_debug, bool, 0644);
+DEFINE_CORE_PARAM(initcall_debug, initcall_debug, false, bool, 0644);
 
 #ifdef CONFIG_KALLSYMS
 struct blacklist_entry {
-- 
1.9.1

Re: [PATCH 1/3] kernel: Add a new config option to remove command line parsing

[Tim Bird]

On 04/01/2015 07:34 AM, Iulia Manda wrote:
> This patch introduces CONFIG_CMDLINE_PARSE option which conditionally compiles
> the support for parsing kernel command line arguments. The corresponding
> functions that actually do the parsing will be compiled out. 
> 
> This is used when no parameters will be specified neither at compile time nor at
> boot time.
> 
> Bloat-o-meter output (compared to the preivous version in which builtin cmdline
> was also set to 'Y'):
> 
> add/remove: 0/8 grow/shrink: 0/6 up/down: 0/-3669 (-3669)

I think this is great stuff.  (Of course, having research something like this
previously, I'm a bit biased.)

It's very nice to have the Bloat-o-meter output for these kernel size shrinking
patches.

The patch itself looks very straightforward, and I don't see any problems
in a visual inspection.

You can add a Reviewed-by: Tim Bird <tim.bird@sonymobile.com> to this patch.

I'd like to be able to point people to this on the mailing list.  In the future
can you make sure to CC: <linux-kernel@vger.kernel.org>, so there's a reference
on lkml.org I can point people to?

Thanks for this great work!
 -- Tim

Re: [PATCH 1/3] kernel: Add a new config option to remove command line parsing

[Rob Landley]

On Mon, May 18, 2015 at 6:50 AM, Iulia Manda <iulia.manda21@gmail.com> wrote:
> This patch introduces CONFIG_CMDLINE_PARSE option which conditionally
> compiles the support for parsing kernel command line arguments. The
> corresponding functions that actually do the parsing will be compiled out.

Could you make it depend on EXPERT?

Thanks,

Rob

Re: [PATCH 1/3] kernel: Add a new config option to remove command line parsing

[josh]

On Tue, May 19, 2015 at 11:35:59AM +0200, Paul Bolle wrote:
> On Mon, 2015-05-18 at 14:50 +0300, Iulia Manda wrote:
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> 
> > +config CMDLINE_PARSE
> > +	bool "Enable support for command line parsing"
> > +	default y
> > +	---help---
> > +	  With this option set to 'Y', kernel parameters, both the ones
> > +	  passed at boot time and at compile time are parsed.
> > +
> > +	  If you say no here, all the kernel parameters' values will be set
> > +	  to their defaults at compile time, in order to make constant
> > +	  folding possible.
> > +
> > +	  Systems with no space constraints should leave this option set to
> > +	  'Y'.
> 
> This adds a x86 specific Kconfig option.

Good catch.  I reviewed the Kconfig option and its usage very carefully,
but completely missed that it was in the wrong file.

This needs to go in init/Kconfig or similar.

- Josh Triplett

Re: [PATCH 1/3] kernel: Add a new config option to remove command line parsing

[Paul Bolle]

On Mon, 2015-05-18 at 14:50 +0300, Iulia Manda wrote:
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig

> +config CMDLINE_PARSE
> +	bool "Enable support for command line parsing"
> +	default y
> +	---help---
> +	  With this option set to 'Y', kernel parameters, both the ones
> +	  passed at boot time and at compile time are parsed.
> +
> +	  If you say no here, all the kernel parameters' values will be set
> +	  to their defaults at compile time, in order to make constant
> +	  folding possible.
> +
> +	  Systems with no space constraints should leave this option set to
> +	  'Y'.

This adds a x86 specific Kconfig option.

> --- a/include/linux/moduleparam.h
> +++ b/include/linux/moduleparam.h
 
> +#ifdef CONFIG_CMDLINE_PARSE
>  /* Called on module insert or kernel boot */
>  extern char *parse_args(const char *name,
>  		      char *args,
> @@ -359,6 +360,19 @@ extern char *parse_args(const char *name,
>  		      s16 level_max,
>  		      int (*unknown)(char *param, char *val,
>  			      const char *doing));
> +#else
> +static inline char *parse_args(const char *name,
> +		      char *args,
> +		      const struct kernel_param *params,
> +		      unsigned num,
> +		      s16 level_min,
> +		      s16 level_max,
> +		      int (*unknown)(char *param, char *val,
> +			      const char *doing))
> +{
> +	return NULL;
> +}
> +#endif

So this effectively disables parse_args() for all architectures, doesn't
it? If that's OK, I'd say the patch is x86 specific. Than it should
have, say, "x86:" as a prefix and it should be sent to the people and
lists taking care of x86.

But a quick grep suggests it's not OK to disable this for all other
architectures. Did I miss something with that quick grep?

Thanks,


Paul Bolle

[PATCH 1/3] kernel: Add a new config option to remove command line parsing

[Iulia Manda]

This patch introduces CONFIG_CMDLINE_PARSE option which conditionally
compiles the support for parsing kernel command line arguments. The
corresponding functions that actually do the parsing will be compiled out.

This is used when no parameters will be specified neither at compile time
nor at boot time.

Bloat-o-meter output (compared to the version in which builtin
cmdline is set to 'Y'):

add/remove: 0/8 grow/shrink: 0/6 up/down: 0/-3669 (-3669)
function                                     old     new   delta
load_module                                 5571    5563      -8
parse_early_param                             54      44     -10
parse_early_options                           33       5     -28
initcall_level_names                          32       -     -32
kernel_init_freeable                         413     360     -53
unknown_module_param_cb                       60       -     -60
setup_arch                                  3041    2972     -69
set_init_arg                                  73       -     -73
repair_env_string                             81       -     -81
start_kernel                                 857     759     -98
do_early_param                               117       -    -117
unknown_bootoption                           366       -    -366
parse_args                                   626       -    -626
builtin_cmdline                             2048       -   -2048

Signed-off-by: Iulia Manda <iulia.manda21@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Tim Bird <tim.bird@sonymobile.com>
---
 arch/x86/Kconfig            | 15 +++++++++++++++
 include/linux/moduleparam.h | 14 ++++++++++++++
 kernel/params.c             |  2 ++
 3 files changed, 31 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6049d58..daabbc3 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2002,8 +2002,23 @@ config COMPAT_VDSO
 	  If unsure, say N: if you are compiling your own kernel, you
 	  are unlikely to be using a buggy version of glibc.
 
+config CMDLINE_PARSE
+	bool "Enable support for command line parsing"
+	default y
+	---help---
+	  With this option set to 'Y', kernel parameters, both the ones
+	  passed at boot time and at compile time are parsed.
+
+	  If you say no here, all the kernel parameters' values will be set
+	  to their defaults at compile time, in order to make constant
+	  folding possible.
+
+	  Systems with no space constraints should leave this option set to
+	  'Y'.
+
 config CMDLINE_BOOL
 	bool "Built-in kernel command line"
+	depends on CMDLINE_PARSE
 	---help---
 	  Allow for specifying boot arguments to the kernel at
 	  build time.  On some systems (e.g. embedded ones), it is
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 1c9effa..570f70e 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -350,6 +350,7 @@ extern bool parameq(const char *name1, const char *name2);
  */
 extern bool parameqn(const char *name1, const char *name2, size_t n);
 
+#ifdef CONFIG_CMDLINE_PARSE
 /* Called on module insert or kernel boot */
 extern char *parse_args(const char *name,
 		      char *args,
@@ -359,6 +360,19 @@ extern char *parse_args(const char *name,
 		      s16 level_max,
 		      int (*unknown)(char *param, char *val,
 			      const char *doing));
+#else
+static inline char *parse_args(const char *name,
+		      char *args,
+		      const struct kernel_param *params,
+		      unsigned num,
+		      s16 level_min,
+		      s16 level_max,
+		      int (*unknown)(char *param, char *val,
+			      const char *doing))
+{
+	return NULL;
+}
+#endif
 
 /* Called by module remove. */
 #ifdef CONFIG_SYSFS
diff --git a/kernel/params.c b/kernel/params.c
index 728e05b..d3bfe47 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -93,6 +93,7 @@ static void param_check_unsafe(const struct kernel_param *kp)
 	}
 }
 
+#ifdef CONFIG_CMDLINE_PARSE
 static int parse_one(char *param,
 		     char *val,
 		     const char *doing,
@@ -239,6 +240,7 @@ char *parse_args(const char *doing,
 	/* All parsed OK. */
 	return NULL;
 }
+#endif
 
 /* Lazy bastard, eh? */
 #define STANDARD_PARAM_DEF(name, type, format, strtolfn)      		\
-- 
1.8.3.2