[OpenWrt-Devel] [PATCH v4 2/2] kernel: rework module stripping, add Kconfig option

Daniel Santos daniel.santos at pobox.com
Sun Nov 4 16:33:48 EST 2018 

Add an option to the "Global build settings" menu to choose if and how
kernel modules are stripped.  Stripping is now performed upon install
into staging, leaving modules in the kernel build tree untouched so that
they are useful for remote debugging and such.

The user will now be allowed to choose to 1.) leave modules unstripped,
2.) strip unneeded symbols and sections, or 3.) strip all -- the later
of which exposes access to Felix's hack for removing non-essential
module information.  Thus, rather than having to go to the
kernel_menuconfig to disable it when not desired, it can be disabled
simply by selecting either "strip unneeded" or "strip none".  The
functionality of "strip all" and Felix's patch are logical mates.
Although it is concievable that one may want to retain author, parameter
descriptions, etc., but also do a strip-all, this can still be done by
disabling Felix's patch via kernel_menuconfig.

The kernel .config option MODULE_STRIPPED is renamed to MODULE_STRIP_ALL
for disabiguation while the options to not strip or only strip-unneeded
are not exported to the kernel .config as they are only relevent to the
OpenWRT build.

Signed-off-by: Daniel Santos <daniel.santos at pobox.com>
---
 config/Config-build.in                             | 29 ++++++++++++++++++++++
 include/kernel.mk                                  | 17 +++++++++++--
 target/linux/generic/config-4.14                   |  1 -
 target/linux/generic/config-4.9                    |  1 -
 .../linux/generic/hack-4.14/204-module_strip.patch | 22 ++++++++--------
 .../linux/generic/hack-4.9/204-module_strip.patch  | 24 +++++++++---------
 6 files changed, 67 insertions(+), 27 deletions(-)

diff --git a/config/Config-build.in b/config/Config-build.in
index a082a5e0e2..72076d0648 100644
--- a/config/Config-build.in
+++ b/config/Config-build.in
@@ -151,6 +151,35 @@ menu "Global build settings"
 		  image.  Note that this might make the kernel incompatible with any kernel
 		  modules that were not selected at the time the kernel image was created.
 
+	choice
+		prompt "Kernel module stripping"
+		default KERNEL_MODULE_STRIP_ALL
+		help
+		  If and how modules should be stripped upon install.  Modules
+		  in the Linux build tree remain unchanged.
+
+		config MODULE_STRIP_NONE
+			bool "strip none"
+			help
+			  Will install modules exactly as they are built in the
+			  tree, including any debug symbols if enabled in the
+			  Kernel Hacking menuconfig menu.
+
+		config MODULE_STRIP_UNNEEDED
+			bool "strip unneeded"
+			help
+			  Strips all unneeded symbols from modules as they are
+			  installed.
+
+		config KERNEL_MODULE_STRIP_ALL
+			bool "strip all"
+			help
+			  Further reduces size of kernel modules by stripping
+			  all symbols, including relocations, and removing
+			  customary strings such as author, version, parameter
+			  descriptions, etc.
+	endchoice
+
 	config USE_MKLIBS
 		bool "Strip unnecessary functions from libraries"
 		help
diff --git a/include/kernel.mk b/include/kernel.mk
index 62a8e99e2d..251ac1c94c 100644
--- a/include/kernel.mk
+++ b/include/kernel.mk
@@ -122,6 +122,18 @@ ifdef CONFIG_USE_SPARSE
   KERNEL_MAKEOPTS += C=1 CHECK=$(STAGING_DIR_HOST)/bin/sparse
 endif
 
+# Define command for copying kernel modules.
+ifeq ($(CONFIG_MODULE_STRIP_NONE),y)
+  MODULE_COPY := $(CP) -L
+else
+  MODULE_COPY = $(KERNEL_CROSS)objcopy
+  ifeq ($(CONFIG_MODULE_STRIP_UNNEEDED),y)
+    MODULE_COPY += --strip-unneeded
+  else # CONFIG_MODULE_STRIP_ALL
+    MODULE_COPY += --strip-all
+  endif
+endif
+
 PKG_EXTMOD_SUBDIRS ?= .
 
 define populate_module_symvers
@@ -229,8 +241,9 @@ $(call KernelPackage/$(1)/config)
 			if grep -q "$$$$$$$${mod##$(LINUX_DIR)/}" "$(LINUX_DIR)/modules.builtin"; then \
 				echo "NOTICE: module '$$$$$$$$mod' is built-in."; \
 			elif [ -e $$$$$$$$mod ]; then \
-				mkdir -p $$(1)/$(MODULES_SUBDIR) ; \
-				$(CP) -L $$$$$$$$mod $$(1)/$(MODULES_SUBDIR)/ ; \
+				mkdir -p $$(1)/$(MODULES_SUBDIR); \
+				mod_name=`basename $$$$$$$$mod`; \
+				$(MODULE_COPY) $$$$$$$$mod $$(1)/$(MODULES_SUBDIR)/$$$$$$$$mod_name; \
 			else \
 				echo "ERROR: module '$$$$$$$$mod' is missing." >&2; \
 				exit 1; \
diff --git a/target/linux/generic/config-4.14 b/target/linux/generic/config-4.14
index 97207cf2eb..8a12b422cb 100644
--- a/target/linux/generic/config-4.14
+++ b/target/linux/generic/config-4.14
@@ -2674,7 +2674,6 @@ CONFIG_MODULES=y
 # CONFIG_MODULE_FORCE_UNLOAD is not set
 # CONFIG_MODULE_SIG is not set
 # CONFIG_MODULE_SRCVERSION_ALL is not set
-CONFIG_MODULE_STRIPPED=y
 CONFIG_MODULE_UNLOAD=y
 # CONFIG_MODVERSIONS is not set
 # CONFIG_MOST is not set
diff --git a/target/linux/generic/config-4.9 b/target/linux/generic/config-4.9
index 979028f04a..18cf72e75e 100644
--- a/target/linux/generic/config-4.9
+++ b/target/linux/generic/config-4.9
@@ -2502,7 +2502,6 @@ CONFIG_MODULES=y
 # CONFIG_MODULE_FORCE_UNLOAD is not set
 # CONFIG_MODULE_SIG is not set
 # CONFIG_MODULE_SRCVERSION_ALL is not set
-CONFIG_MODULE_STRIPPED=y
 CONFIG_MODULE_UNLOAD=y
 # CONFIG_MODVERSIONS is not set
 # CONFIG_MOST is not set
diff --git a/target/linux/generic/hack-4.14/204-module_strip.patch b/target/linux/generic/hack-4.14/204-module_strip.patch
index db65062fcf..6ddc6a7312 100644
--- a/target/linux/generic/hack-4.14/204-module_strip.patch
+++ b/target/linux/generic/hack-4.14/204-module_strip.patch
@@ -34,7 +34,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
 +#define MODULE_DESCRIPTION(_description) MODULE_INFO_STRIP(description, _description)
  
 -#ifdef MODULE
-+#if defined(MODULE) && !defined(CONFIG_MODULE_STRIPPED)
++#if defined(MODULE) && !defined(CONFIG_MODULE_STRIP_ALL)
  /* Creates an alias so file2alias.c can find device table. */
  #define MODULE_DEVICE_TABLE(type, name)					\
  extern typeof(name) __mod_##type##__##name##_device_table		\
@@ -44,7 +44,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  #if defined(MODULE) || !defined(CONFIG_SYSFS)
 -#define MODULE_VERSION(_version) MODULE_INFO(version, _version)
 +#define MODULE_VERSION(_version) MODULE_INFO_STRIP(version, _version)
-+#elif defined(CONFIG_MODULE_STRIPPED)
++#elif defined(CONFIG_MODULE_STRIP_ALL)
 +#define MODULE_VERSION(_version) __MODULE_INFO_DISABLED(version)
  #else
  #define MODULE_VERSION(_version)					\
@@ -68,7 +68,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
 +#define __MODULE_INFO_DISABLED(name)					  \
 +  struct __UNIQUE_ID(name) {}
 +
-+#ifdef CONFIG_MODULE_STRIPPED
++#ifdef CONFIG_MODULE_STRIP_ALL
 +#define __MODULE_INFO_STRIP(tag, name, info) __MODULE_INFO_DISABLED(name)
 +#else
 +#define __MODULE_INFO_STRIP(tag, name, info) __MODULE_INFO(tag, name, info)
@@ -102,7 +102,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  
  	  If unsure, or if you need to build out-of-tree modules, say N.
  
-+config MODULE_STRIPPED
++config MODULE_STRIP_ALL
 +	bool "Reduce module size"
 +	depends on MODULES
 +	help
@@ -121,7 +121,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
 -	const char *modmagic = get_modinfo(info, "vermagic");
  	int err;
  
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
 +	const char *modmagic = get_modinfo(info, "vermagic");
 +
  	if (flags & MODULE_INIT_IGNORE_VERMAGIC)
@@ -141,7 +141,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  		symname = remove_dot(info.strtab + sym->st_name);
  
  		handle_modversions(mod, &info, sym, symname);
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  		handle_moddevtable(mod, &info, sym, symname);
 +#endif
  	}
@@ -151,7 +151,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  	buf_printf(b, "#include <linux/vermagic.h>\n");
  	buf_printf(b, "#include <linux/compiler.h>\n");
  	buf_printf(b, "\n");
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  	buf_printf(b, "MODULE_INFO(vermagic, VERMAGIC_STRING);\n");
  	buf_printf(b, "MODULE_INFO(name, KBUILD_MODNAME);\n");
 +#endif
@@ -162,7 +162,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  
  static void add_intree_flag(struct buffer *b, int is_intree)
  {
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  	if (is_intree)
  		buf_printf(b, "\nMODULE_INFO(intree, \"Y\");\n");
 +#endif
@@ -173,7 +173,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  
  static void add_staging_flag(struct buffer *b, const char *name)
  {
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  	static const char *staging_dir = "drivers/staging";
  
  	if (strncmp(staging_dir, name, strlen(staging_dir)) == 0)
@@ -186,7 +186,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  
  static void add_srcversion(struct buffer *b, struct module *mod)
  {
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  	if (mod->srcversion[0]) {
  		buf_printf(b, "\n");
  		buf_printf(b, "MODULE_INFO(srcversion, \"%s\");\n",
@@ -200,7 +200,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  		add_staging_flag(&buf, mod->name);
  		err |= add_versions(&buf, mod);
  		add_depends(&buf, mod, modules);
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  		add_moddevtable(&buf, mod);
 +#endif
  		add_srcversion(&buf, mod);
diff --git a/target/linux/generic/hack-4.9/204-module_strip.patch b/target/linux/generic/hack-4.9/204-module_strip.patch
index c6484a8f92..68707422a3 100644
--- a/target/linux/generic/hack-4.9/204-module_strip.patch
+++ b/target/linux/generic/hack-4.9/204-module_strip.patch
@@ -34,7 +34,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
 +#define MODULE_DESCRIPTION(_description) MODULE_INFO_STRIP(description, _description)
  
 -#ifdef MODULE
-+#if defined(MODULE) && !defined(CONFIG_MODULE_STRIPPED)
++#if defined(MODULE) && !defined(CONFIG_MODULE_STRIP_ALL)
  /* Creates an alias so file2alias.c can find device table. */
  #define MODULE_DEVICE_TABLE(type, name)					\
  extern const typeof(name) __mod_##type##__##name##_device_table		\
@@ -44,7 +44,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  #if defined(MODULE) || !defined(CONFIG_SYSFS)
 -#define MODULE_VERSION(_version) MODULE_INFO(version, _version)
 +#define MODULE_VERSION(_version) MODULE_INFO_STRIP(version, _version)
-+#elif defined(CONFIG_MODULE_STRIPPED)
++#elif defined(CONFIG_MODULE_STRIP_ALL)
 +#define MODULE_VERSION(_version) __MODULE_INFO_DISABLED(version)
  #else
  #define MODULE_VERSION(_version)					\
@@ -68,7 +68,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
 +#define __MODULE_INFO_DISABLED(name)					  \
 +  struct __UNIQUE_ID(name) {}
 +
-+#ifdef CONFIG_MODULE_STRIPPED
++#ifdef CONFIG_MODULE_STRIP_ALL
 +#define __MODULE_INFO_STRIP(tag, name, info) __MODULE_INFO_DISABLED(name)
 +#else
 +#define __MODULE_INFO_STRIP(tag, name, info) __MODULE_INFO(tag, name, info)
@@ -102,7 +102,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  
  	  If unsure, or if you need to build out-of-tree modules, say N.
  
-+config MODULE_STRIPPED
++config MODULE_STRIP_ALL
 +	bool "Reduce module size"
 +	depends on MODULES
 +	help
@@ -121,7 +121,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
 -	const char *modmagic = get_modinfo(info, "vermagic");
  	int err;
  
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
 +	const char *modmagic = get_modinfo(info, "vermagic");
 +
  	if (flags & MODULE_INIT_IGNORE_VERMAGIC)
@@ -141,7 +141,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  		symname = remove_dot(info.strtab + sym->st_name);
  
  		handle_modversions(mod, &info, sym, symname);
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  		handle_moddevtable(mod, &info, sym, symname);
 +#endif
  	}
@@ -151,7 +151,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  	buf_printf(b, "#include <linux/vermagic.h>\n");
  	buf_printf(b, "#include <linux/compiler.h>\n");
  	buf_printf(b, "\n");
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  	buf_printf(b, "MODULE_INFO(vermagic, VERMAGIC_STRING);\n");
 +#endif
  	buf_printf(b, "\n");
@@ -161,7 +161,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  
  static void add_intree_flag(struct buffer *b, int is_intree)
  {
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  	if (is_intree)
  		buf_printf(b, "\nMODULE_INFO(intree, \"Y\");\n");
 +#endif
@@ -170,7 +170,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  /* Cannot check for assembler */
  static void add_retpoline(struct buffer *b)
  {
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  	buf_printf(b, "\n#ifdef RETPOLINE\n");
  	buf_printf(b, "MODULE_INFO(retpoline, \"Y\");\n");
  	buf_printf(b, "#endif\n");
@@ -179,7 +179,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  
  static void add_staging_flag(struct buffer *b, const char *name)
  {
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  	static const char *staging_dir = "drivers/staging";
  
  	if (strncmp(staging_dir, name, strlen(staging_dir)) == 0)
@@ -192,7 +192,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  
  static void add_srcversion(struct buffer *b, struct module *mod)
  {
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  	if (mod->srcversion[0]) {
  		buf_printf(b, "\n");
  		buf_printf(b, "MODULE_INFO(srcversion, \"%s\");\n",
@@ -206,7 +206,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  		add_staging_flag(&buf, mod->name);
  		err |= add_versions(&buf, mod);
  		add_depends(&buf, mod, modules);
-+#ifndef CONFIG_MODULE_STRIPPED
++#ifndef CONFIG_MODULE_STRIP_ALL
  		add_moddevtable(&buf, mod);
 +#endif
  		add_srcversion(&buf, mod);
-- 
2.16.4


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