[PATCH v6 0/4] bootconfig: Support embedding a bootconfig in kernel for non initrd boot

[PATCH v6 0/4] bootconfig: Support embedding a bootconfig in kernel for non initrd boot

[Masami Hiramatsu]

Hi,

Here are the 6th version of the patchset to enable kernel embedded bootconfig
for non-initrd kernel boot environment. This version adds a new patch to use
obj-y instead of lib-y for bootconfig([1/4]) and split the inline asm code into
independent asm file for incremental build with LTO THIN mode issue(*), which
was reported in the previous version [1].

[1] https://lore.kernel.org/all/164847778869.3060675.8115416881394543419.stgit@devnote2/T/#u

You can embed a bootconfig file into the kernel as a default bootconfig,
which will be used if there is no initrd or no bootconfig is attached to initrd. 

This needs 2 options: CONFIG_EMBED_BOOT_CONFIG=y and set the file
path to CONFIG_EMBED_BOOT_CONFIG_FILE. Even if you embed the bootconfig file
to the kernel, it will not be enabled unless you pass "bootconfig" kernel
command line option at boot. Moreover, since this is just a "default"
bootconfig, you can override it with a new bootconfig if you attach another
bootconfig to the initrd (if possible).
CONFIG_EMBED_BOOT_CONFIG_FILE can take both absolute and relative path, but
to simplify and make it independent from the build environment, I recommend
you to use an absolute path for that.

This is requested by Padmanabha at the below thread[2];

[2] https://lore.kernel.org/all/20220307184011.GA2570@pswork/T/#u

(*) this issue has been reported to github ClangBuiltLinux project [3]

[3] https://github.com/ClangBuiltLinux/linux/issues/1618

and Nick told me that we can avoid this by disabling LTO on that file.

CFLAGS_REMOVE_<file>.o := $(CC_FLAGS_LTO)

But I chose Masahiro's idea to split the inline asm into an independent
asm file, since that can also simplify the Makefile.
The above mitigation should be applied to kernel/configs.c and kernel/kheaders.c
but that should be another story (maybe LTO bugfix?).


Thank you,

---

Masami Hiramatsu (4):
      bootconfig: Make the bootconfig.o as a normal object file
      bootconfig: Check the checksum before removing the bootconfig from initrd
      bootconfig: Support embedding a bootconfig file in kernel
      docs: bootconfig: Add how to embed the bootconfig into kernel


 Documentation/admin-guide/bootconfig.rst |   31 +++++++++++++++++++++++++++---
 MAINTAINERS                              |    1 +
 include/linux/bootconfig.h               |   10 ++++++++++
 init/Kconfig                             |   21 ++++++++++++++++++++
 init/main.c                              |   31 +++++++++++++++---------------
 lib/.gitignore                           |    1 +
 lib/Makefile                             |   10 +++++++++-
 lib/bootconfig-data.S                    |   11 +++++++++++
 lib/bootconfig.c                         |   13 +++++++++++++
 9 files changed, 110 insertions(+), 19 deletions(-)
 create mode 100644 lib/bootconfig-data.S

--
Masami Hiramatsu (Linaro) <mhiramat@kernel.org>

[PATCH v6 1/4] bootconfig: Make the bootconfig.o as a normal object file

[Masami Hiramatsu]

Since the APIs defined in the bootconfig.o are not individually used,
it is meaningless to build it as library by lib-y. Use obj-y for that.

Reported-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Changes in v6:
  - Newly added.
---
 lib/Makefile |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/Makefile b/lib/Makefile
index 6b9ffc1bd1ee..08053df16c7c 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -279,7 +279,7 @@ $(foreach file, $(libfdt_files), \
 	$(eval CFLAGS_$(file) = -I $(srctree)/scripts/dtc/libfdt))
 lib-$(CONFIG_LIBFDT) += $(libfdt_files)
 
-lib-$(CONFIG_BOOT_CONFIG) += bootconfig.o
+obj-$(CONFIG_BOOT_CONFIG) += bootconfig.o
 
 obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
 obj-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o

[PATCH v6 2/4] bootconfig: Check the checksum before removing the bootconfig from initrd

[Masami Hiramatsu]

Check the bootconfig's checksum before removing the bootcinfig data
from initrd to avoid modifying initrd by mistake.
This will also simplifies the get_boot_config_from_initrd() interface.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 init/main.c |   22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/init/main.c b/init/main.c
index 98182c3c2c4b..266d61bc67b0 100644
--- a/init/main.c
+++ b/init/main.c
@@ -266,7 +266,7 @@ static int __init loglevel(char *str)
 early_param("loglevel", loglevel);
 
 #ifdef CONFIG_BLK_DEV_INITRD
-static void * __init get_boot_config_from_initrd(u32 *_size, u32 *_csum)
+static void * __init get_boot_config_from_initrd(u32 *_size)
 {
 	u32 size, csum;
 	char *data;
@@ -300,17 +300,20 @@ static void * __init get_boot_config_from_initrd(u32 *_size, u32 *_csum)
 		return NULL;
 	}
 
+	if (xbc_calc_checksum(data, size) != csum) {
+		pr_err("bootconfig checksum failed\n");
+		return NULL;
+	}
+
 	/* Remove bootconfig from initramfs/initrd */
 	initrd_end = (unsigned long)data;
 	if (_size)
 		*_size = size;
-	if (_csum)
-		*_csum = csum;
 
 	return data;
 }
 #else
-static void * __init get_boot_config_from_initrd(u32 *_size, u32 *_csum)
+static void * __init get_boot_config_from_initrd(u32 *_size)
 {
 	return NULL;
 }
@@ -409,12 +412,12 @@ static void __init setup_boot_config(void)
 	static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
 	const char *msg;
 	int pos;
-	u32 size, csum;
+	u32 size;
 	char *data, *err;
 	int ret;
 
 	/* Cut out the bootconfig data even if we have no bootconfig option */
-	data = get_boot_config_from_initrd(&size, &csum);
+	data = get_boot_config_from_initrd(&size);
 
 	strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
 	err = parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0, NULL,
@@ -438,11 +441,6 @@ static void __init setup_boot_config(void)
 		return;
 	}
 
-	if (xbc_calc_checksum(data, size) != csum) {
-		pr_err("bootconfig checksum failed\n");
-		return;
-	}
-
 	ret = xbc_init(data, size, &msg, &pos);
 	if (ret < 0) {
 		if (pos < 0)
@@ -471,7 +469,7 @@ static void __init exit_boot_config(void)
 static void __init setup_boot_config(void)
 {
 	/* Remove bootconfig data from initrd */
-	get_boot_config_from_initrd(NULL, NULL);
+	get_boot_config_from_initrd(NULL);
 }
 
 static int __init warn_bootconfig(char *str)

[PATCH v6 3/4] bootconfig: Support embedding a bootconfig file in kernel

[Masami Hiramatsu]

This allows kernel developer to embed a default bootconfig file in
the kernel instead of embedding it in the initrd. This will be good
for who are using the kernel without initrd, or who needs a default
bootconfigs.
This needs to set two kconfigs: CONFIG_EMBED_BOOT_CONFIG=y and set
the file path to CONFIG_EMBED_BOOT_CONFIG_FILE.

Note that you still need 'bootconfig' command line option to load the
embedded bootconfig. Also if you boot using an initrd with a different
bootconfig, the kernel will use the bootconfig in the initrd, instead
of the default bootconfig.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Changes in v6:
  - Split out the .incbin asm part as bootconfig-data.S according to
    Masahiro's comment.
 Changes in v5:
  - Fix .gitignore to be sorted alphabetically.
  - Make default.bconf is cleaned up correctly.
  - Allow user to specify relative path to CONFIG_EMBED_BOOT_CONFIG_FILE.
    (Thanks Masahiro!)
 Changes in v4:
  - Avoid updating the default.bconf if the file is not changed.
---
 MAINTAINERS                |    1 +
 include/linux/bootconfig.h |   10 ++++++++++
 init/Kconfig               |   21 +++++++++++++++++++++
 init/main.c                |   13 ++++++++-----
 lib/.gitignore             |    1 +
 lib/Makefile               |    8 ++++++++
 lib/bootconfig-data.S      |   11 +++++++++++
 lib/bootconfig.c           |   13 +++++++++++++
 8 files changed, 73 insertions(+), 5 deletions(-)
 create mode 100644 lib/bootconfig-data.S

diff --git a/MAINTAINERS b/MAINTAINERS
index b555a5e8704f..9b4910685412 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7350,6 +7350,7 @@ S:	Maintained
 F:	Documentation/admin-guide/bootconfig.rst
 F:	fs/proc/bootconfig.c
 F:	include/linux/bootconfig.h
+F:	lib/bootconfig-data.S
 F:	lib/bootconfig.c
 F:	tools/bootconfig/*
 F:	tools/bootconfig/scripts/*
diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
index a4665c7ab07c..5dbda5e3e9bb 100644
--- a/include/linux/bootconfig.h
+++ b/include/linux/bootconfig.h
@@ -289,4 +289,14 @@ int __init xbc_get_info(int *node_size, size_t *data_size);
 /* XBC cleanup data structures */
 void __init xbc_exit(void);
 
+/* XBC embedded bootconfig data in kernel */
+#ifdef CONFIG_EMBED_BOOT_CONFIG
+char * __init xbc_get_embedded_bootconfig(size_t *size);
+#else
+static inline char *xbc_get_embedded_bootconfig(size_t *size)
+{
+	return NULL;
+}
+#endif
+
 #endif
diff --git a/init/Kconfig b/init/Kconfig
index 97463a33baa7..f5d14a78cfce 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1361,6 +1361,27 @@ config BOOT_CONFIG
 
 	  If unsure, say Y.
 
+config EMBED_BOOT_CONFIG
+	bool "Embed bootconfig file in the kernel"
+	depends on BOOT_CONFIG
+	default n
+	help
+	  Embed a bootconfig file given by EMBED_BOOT_CONFIG_FILE in the
+	  kernel. Usually, the bootconfig file is loaded with the initrd
+	  image. But if the system doesn't support initrd, this option will
+	  help you by embedding a bootconfig file while building the kernel.
+
+	  If unsure, say N.
+
+config EMBED_BOOT_CONFIG_FILE
+	string "Embedded bootconfig file path"
+	default ""
+	depends on EMBED_BOOT_CONFIG
+	help
+	  Specify a bootconfig file which will be embedded to the kernel.
+	  This bootconfig will be used if there is no initrd or no other
+	  bootconfig in the initrd.
+
 choice
 	prompt "Compiler optimization level"
 	default CC_OPTIMIZE_FOR_PERFORMANCE
diff --git a/init/main.c b/init/main.c
index 266d61bc67b0..a5db3e36b809 100644
--- a/init/main.c
+++ b/init/main.c
@@ -266,7 +266,7 @@ static int __init loglevel(char *str)
 early_param("loglevel", loglevel);
 
 #ifdef CONFIG_BLK_DEV_INITRD
-static void * __init get_boot_config_from_initrd(u32 *_size)
+static void * __init get_boot_config_from_initrd(size_t *_size)
 {
 	u32 size, csum;
 	char *data;
@@ -412,12 +412,15 @@ static void __init setup_boot_config(void)
 	static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
 	const char *msg;
 	int pos;
-	u32 size;
+	size_t size;
 	char *data, *err;
 	int ret;
 
 	/* Cut out the bootconfig data even if we have no bootconfig option */
 	data = get_boot_config_from_initrd(&size);
+	/* If there is no bootconfig in initrd, try embedded one. */
+	if (!data)
+		data = xbc_get_embedded_bootconfig(&size);
 
 	strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
 	err = parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0, NULL,
@@ -436,8 +439,8 @@ static void __init setup_boot_config(void)
 	}
 
 	if (size >= XBC_DATA_MAX) {
-		pr_err("bootconfig size %d greater than max size %d\n",
-			size, XBC_DATA_MAX);
+		pr_err("bootconfig size %ld greater than max size %d\n",
+			(long)size, XBC_DATA_MAX);
 		return;
 	}
 
@@ -450,7 +453,7 @@ static void __init setup_boot_config(void)
 				msg, pos);
 	} else {
 		xbc_get_info(&ret, NULL);
-		pr_info("Load bootconfig: %d bytes %d nodes\n", size, ret);
+		pr_info("Load bootconfig: %ld bytes %d nodes\n", (long)size, ret);
 		/* keys starting with "kernel." are passed via cmdline */
 		extra_command_line = xbc_make_cmdline("kernel");
 		/* Also, "init." keys are init arguments */
diff --git a/lib/.gitignore b/lib/.gitignore
index e5e217b8307b..54596b634ecb 100644
--- a/lib/.gitignore
+++ b/lib/.gitignore
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 /crc32table.h
 /crc64table.h
+/default.bconf
 /gen_crc32table
 /gen_crc64table
 /oid_registry_data.c
diff --git a/lib/Makefile b/lib/Makefile
index 08053df16c7c..2a82cc324f91 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -280,6 +280,14 @@ $(foreach file, $(libfdt_files), \
 lib-$(CONFIG_LIBFDT) += $(libfdt_files)
 
 obj-$(CONFIG_BOOT_CONFIG) += bootconfig.o
+obj-$(CONFIG_EMBED_BOOT_CONFIG) += bootconfig-data.o
+
+$(obj)/bootconfig-data.o: $(obj)/default.bconf
+
+targets += default.bconf
+filechk_defbconf = cat $(or $(real-prereqs), /dev/null)
+$(obj)/default.bconf: $(CONFIG_EMBED_BOOT_CONFIG_FILE) FORCE
+	$(call filechk,defbconf)
 
 obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
 obj-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o
diff --git a/lib/bootconfig-data.S b/lib/bootconfig-data.S
new file mode 100644
index 000000000000..df674ea7d8be
--- /dev/null
+++ b/lib/bootconfig-data.S
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Embed default bootconfig in the kernel.
+ */
+	.pushsection .init.data, "aw"
+	.global embedded_bootconfig_data
+embedded_bootconfig_data:
+	.incbin "lib/default.bconf"
+	.global embedded_bootconfig_data_end
+embedded_bootconfig_data_end:
+	.popsection
diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index 74f3201ab8e5..6d30aee85ebe 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -12,6 +12,19 @@
 #include <linux/kernel.h>
 #include <linux/memblock.h>
 #include <linux/string.h>
+
+#ifdef CONFIG_EMBED_BOOT_CONFIG
+/* embedded_bootconfig_data is defined in bootconfig-data.S */
+extern __visible char embedded_bootconfig_data[];
+extern __visible char embedded_bootconfig_data_end[];
+
+char * __init xbc_get_embedded_bootconfig(size_t *size)
+{
+	*size = embedded_bootconfig_data_end - embedded_bootconfig_data;
+	return (*size) ? embedded_bootconfig_data : NULL;
+}
+#endif
+
 #else /* !__KERNEL__ */
 /*
  * NOTE: This is only for tools/bootconfig, because tools/bootconfig will

Re: [PATCH v6 3/4] bootconfig: Support embedding a bootconfig file in kernel

[Masahiro Yamada]

On Thu, Mar 31, 2022 at 2:56 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> This allows kernel developer to embed a default bootconfig file in
> the kernel instead of embedding it in the initrd. This will be good
> for who are using the kernel without initrd, or who needs a default
> bootconfigs.
> This needs to set two kconfigs: CONFIG_EMBED_BOOT_CONFIG=y and set
> the file path to CONFIG_EMBED_BOOT_CONFIG_FILE.
>
> Note that you still need 'bootconfig' command line option to load the
> embedded bootconfig. Also if you boot using an initrd with a different
> bootconfig, the kernel will use the bootconfig in the initrd, instead
> of the default bootconfig.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  Changes in v6:
>   - Split out the .incbin asm part as bootconfig-data.S according to
>     Masahiro's comment.
>  Changes in v5:
>   - Fix .gitignore to be sorted alphabetically.
>   - Make default.bconf is cleaned up correctly.
>   - Allow user to specify relative path to CONFIG_EMBED_BOOT_CONFIG_FILE.
>     (Thanks Masahiro!)
>  Changes in v4:
>   - Avoid updating the default.bconf if the file is not changed.
> ---
>  MAINTAINERS                |    1 +
>  include/linux/bootconfig.h |   10 ++++++++++
>  init/Kconfig               |   21 +++++++++++++++++++++
>  init/main.c                |   13 ++++++++-----
>  lib/.gitignore             |    1 +
>  lib/Makefile               |    8 ++++++++
>  lib/bootconfig-data.S      |   11 +++++++++++
>  lib/bootconfig.c           |   13 +++++++++++++
>  8 files changed, 73 insertions(+), 5 deletions(-)
>  create mode 100644 lib/bootconfig-data.S
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index b555a5e8704f..9b4910685412 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -7350,6 +7350,7 @@ S:        Maintained
>  F:     Documentation/admin-guide/bootconfig.rst
>  F:     fs/proc/bootconfig.c
>  F:     include/linux/bootconfig.h
> +F:     lib/bootconfig-data.S
>  F:     lib/bootconfig.c
>  F:     tools/bootconfig/*
>  F:     tools/bootconfig/scripts/*
> diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
> index a4665c7ab07c..5dbda5e3e9bb 100644
> --- a/include/linux/bootconfig.h
> +++ b/include/linux/bootconfig.h
> @@ -289,4 +289,14 @@ int __init xbc_get_info(int *node_size, size_t *data_size);
>  /* XBC cleanup data structures */
>  void __init xbc_exit(void);
>
> +/* XBC embedded bootconfig data in kernel */
> +#ifdef CONFIG_EMBED_BOOT_CONFIG
> +char * __init xbc_get_embedded_bootconfig(size_t *size);
> +#else
> +static inline char *xbc_get_embedded_bootconfig(size_t *size)
> +{
> +       return NULL;
> +}
> +#endif
> +
>  #endif
> diff --git a/init/Kconfig b/init/Kconfig
> index 97463a33baa7..f5d14a78cfce 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1361,6 +1361,27 @@ config BOOT_CONFIG
>
>           If unsure, say Y.
>
> +config EMBED_BOOT_CONFIG
> +       bool "Embed bootconfig file in the kernel"
> +       depends on BOOT_CONFIG
> +       default n
> +       help
> +         Embed a bootconfig file given by EMBED_BOOT_CONFIG_FILE in the
> +         kernel. Usually, the bootconfig file is loaded with the initrd
> +         image. But if the system doesn't support initrd, this option will
> +         help you by embedding a bootconfig file while building the kernel.
> +
> +         If unsure, say N.
> +
> +config EMBED_BOOT_CONFIG_FILE
> +       string "Embedded bootconfig file path"
> +       default ""
> +       depends on EMBED_BOOT_CONFIG
> +       help
> +         Specify a bootconfig file which will be embedded to the kernel.
> +         This bootconfig will be used if there is no initrd or no other
> +         bootconfig in the initrd.
> +
>  choice
>         prompt "Compiler optimization level"
>         default CC_OPTIMIZE_FOR_PERFORMANCE
> diff --git a/init/main.c b/init/main.c
> index 266d61bc67b0..a5db3e36b809 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -266,7 +266,7 @@ static int __init loglevel(char *str)
>  early_param("loglevel", loglevel);
>
>  #ifdef CONFIG_BLK_DEV_INITRD
> -static void * __init get_boot_config_from_initrd(u32 *_size)
> +static void * __init get_boot_config_from_initrd(size_t *_size)
>  {
>         u32 size, csum;
>         char *data;
> @@ -412,12 +412,15 @@ static void __init setup_boot_config(void)
>         static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
>         const char *msg;
>         int pos;
> -       u32 size;
> +       size_t size;
>         char *data, *err;
>         int ret;
>
>         /* Cut out the bootconfig data even if we have no bootconfig option */
>         data = get_boot_config_from_initrd(&size);
> +       /* If there is no bootconfig in initrd, try embedded one. */
> +       if (!data)
> +               data = xbc_get_embedded_bootconfig(&size);
>
>         strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
>         err = parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0, NULL,
> @@ -436,8 +439,8 @@ static void __init setup_boot_config(void)
>         }
>
>         if (size >= XBC_DATA_MAX) {
> -               pr_err("bootconfig size %d greater than max size %d\n",
> -                       size, XBC_DATA_MAX);
> +               pr_err("bootconfig size %ld greater than max size %d\n",
> +                       (long)size, XBC_DATA_MAX);
>                 return;
>         }
>
> @@ -450,7 +453,7 @@ static void __init setup_boot_config(void)
>                                 msg, pos);
>         } else {
>                 xbc_get_info(&ret, NULL);
> -               pr_info("Load bootconfig: %d bytes %d nodes\n", size, ret);
> +               pr_info("Load bootconfig: %ld bytes %d nodes\n", (long)size, ret);
>                 /* keys starting with "kernel." are passed via cmdline */
>                 extra_command_line = xbc_make_cmdline("kernel");
>                 /* Also, "init." keys are init arguments */
> diff --git a/lib/.gitignore b/lib/.gitignore
> index e5e217b8307b..54596b634ecb 100644
> --- a/lib/.gitignore
> +++ b/lib/.gitignore
> @@ -1,6 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  /crc32table.h
>  /crc64table.h
> +/default.bconf
>  /gen_crc32table
>  /gen_crc64table
>  /oid_registry_data.c
> diff --git a/lib/Makefile b/lib/Makefile
> index 08053df16c7c..2a82cc324f91 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -280,6 +280,14 @@ $(foreach file, $(libfdt_files), \
>  lib-$(CONFIG_LIBFDT) += $(libfdt_files)
>
>  obj-$(CONFIG_BOOT_CONFIG) += bootconfig.o
> +obj-$(CONFIG_EMBED_BOOT_CONFIG) += bootconfig-data.o
> +
> +$(obj)/bootconfig-data.o: $(obj)/default.bconf
> +
> +targets += default.bconf
> +filechk_defbconf = cat $(or $(real-prereqs), /dev/null)
> +$(obj)/default.bconf: $(CONFIG_EMBED_BOOT_CONFIG_FILE) FORCE
> +       $(call filechk,defbconf)
>
>  obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
>  obj-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o
> diff --git a/lib/bootconfig-data.S b/lib/bootconfig-data.S
> new file mode 100644
> index 000000000000..df674ea7d8be
> --- /dev/null
> +++ b/lib/bootconfig-data.S
> @@ -0,0 +1,11 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Embed default bootconfig in the kernel.
> + */
> +       .pushsection .init.data, "aw"
> +       .global embedded_bootconfig_data
> +embedded_bootconfig_data:
> +       .incbin "lib/default.bconf"
> +       .global embedded_bootconfig_data_end
> +embedded_bootconfig_data_end:
> +       .popsection



You used  .pushsection / .popsection because it was
previously located in bootconfig.c, where there are
functions, which should go to the ".text" section.


Now that you split this into a separate compilation unit,
there is only one ".init.data" section in the file.


     .section  .init.data, "aw"

should be enough.



BTW, is it reasonable/possible to make it explicitly read-only?

I have not tested this patch at all. Nor do I have enough insight.

     .section  .init.rodata, "a"

I am not sure whether this is possible or not.



Some more nits:

    default n

    default ""

are the redundant defaults in Kconfig.





Personally, I prefer seeing the common prefix
for options that belong to the same group,
for example,

   CONFIG_BOOT_CONFIG
   CONFIG_BOOT_CONFIG_EMBED
   CONFIG_BOOT_CONFIG_EMBEDDED_FILE


But, this is something like "up to you" things.







> diff --git a/lib/bootconfig.c b/lib/bootconfig.c
> index 74f3201ab8e5..6d30aee85ebe 100644
> --- a/lib/bootconfig.c
> +++ b/lib/bootconfig.c
> @@ -12,6 +12,19 @@
>  #include <linux/kernel.h>
>  #include <linux/memblock.h>
>  #include <linux/string.h>
> +
> +#ifdef CONFIG_EMBED_BOOT_CONFIG
> +/* embedded_bootconfig_data is defined in bootconfig-data.S */
> +extern __visible char embedded_bootconfig_data[];
> +extern __visible char embedded_bootconfig_data_end[];
> +
> +char * __init xbc_get_embedded_bootconfig(size_t *size)
> +{
> +       *size = embedded_bootconfig_data_end - embedded_bootconfig_data;
> +       return (*size) ? embedded_bootconfig_data : NULL;
> +}
> +#endif
> +
>  #else /* !__KERNEL__ */
>  /*
>   * NOTE: This is only for tools/bootconfig, because tools/bootconfig will
>


-- 
Best Regards
Masahiro Yamada

Re: [PATCH v6 3/4] bootconfig: Support embedding a bootconfig file in kernel

[Masami Hiramatsu]

On Thu, 31 Mar 2022 15:27:56 +0900
Masahiro Yamada <masahiroy@kernel.org> wrote:

> On Thu, Mar 31, 2022 at 2:56 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
> >
> > This allows kernel developer to embed a default bootconfig file in
> > the kernel instead of embedding it in the initrd. This will be good
> > for who are using the kernel without initrd, or who needs a default
> > bootconfigs.
> > This needs to set two kconfigs: CONFIG_EMBED_BOOT_CONFIG=y and set
> > the file path to CONFIG_EMBED_BOOT_CONFIG_FILE.
> >
> > Note that you still need 'bootconfig' command line option to load the
> > embedded bootconfig. Also if you boot using an initrd with a different
> > bootconfig, the kernel will use the bootconfig in the initrd, instead
> > of the default bootconfig.
> >
> > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> > ---
> >  Changes in v6:
> >   - Split out the .incbin asm part as bootconfig-data.S according to
> >     Masahiro's comment.
> >  Changes in v5:
> >   - Fix .gitignore to be sorted alphabetically.
> >   - Make default.bconf is cleaned up correctly.
> >   - Allow user to specify relative path to CONFIG_EMBED_BOOT_CONFIG_FILE.
> >     (Thanks Masahiro!)
> >  Changes in v4:
> >   - Avoid updating the default.bconf if the file is not changed.
> > ---
> >  MAINTAINERS                |    1 +
> >  include/linux/bootconfig.h |   10 ++++++++++
> >  init/Kconfig               |   21 +++++++++++++++++++++
> >  init/main.c                |   13 ++++++++-----
> >  lib/.gitignore             |    1 +
> >  lib/Makefile               |    8 ++++++++
> >  lib/bootconfig-data.S      |   11 +++++++++++
> >  lib/bootconfig.c           |   13 +++++++++++++
> >  8 files changed, 73 insertions(+), 5 deletions(-)
> >  create mode 100644 lib/bootconfig-data.S
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index b555a5e8704f..9b4910685412 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -7350,6 +7350,7 @@ S:        Maintained
> >  F:     Documentation/admin-guide/bootconfig.rst
> >  F:     fs/proc/bootconfig.c
> >  F:     include/linux/bootconfig.h
> > +F:     lib/bootconfig-data.S
> >  F:     lib/bootconfig.c
> >  F:     tools/bootconfig/*
> >  F:     tools/bootconfig/scripts/*
> > diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
> > index a4665c7ab07c..5dbda5e3e9bb 100644
> > --- a/include/linux/bootconfig.h
> > +++ b/include/linux/bootconfig.h
> > @@ -289,4 +289,14 @@ int __init xbc_get_info(int *node_size, size_t *data_size);
> >  /* XBC cleanup data structures */
> >  void __init xbc_exit(void);
> >
> > +/* XBC embedded bootconfig data in kernel */
> > +#ifdef CONFIG_EMBED_BOOT_CONFIG
> > +char * __init xbc_get_embedded_bootconfig(size_t *size);
> > +#else
> > +static inline char *xbc_get_embedded_bootconfig(size_t *size)
> > +{
> > +       return NULL;
> > +}
> > +#endif
> > +
> >  #endif
> > diff --git a/init/Kconfig b/init/Kconfig
> > index 97463a33baa7..f5d14a78cfce 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -1361,6 +1361,27 @@ config BOOT_CONFIG
> >
> >           If unsure, say Y.
> >
> > +config EMBED_BOOT_CONFIG
> > +       bool "Embed bootconfig file in the kernel"
> > +       depends on BOOT_CONFIG
> > +       default n
> > +       help
> > +         Embed a bootconfig file given by EMBED_BOOT_CONFIG_FILE in the
> > +         kernel. Usually, the bootconfig file is loaded with the initrd
> > +         image. But if the system doesn't support initrd, this option will
> > +         help you by embedding a bootconfig file while building the kernel.
> > +
> > +         If unsure, say N.
> > +
> > +config EMBED_BOOT_CONFIG_FILE
> > +       string "Embedded bootconfig file path"
> > +       default ""
> > +       depends on EMBED_BOOT_CONFIG
> > +       help
> > +         Specify a bootconfig file which will be embedded to the kernel.
> > +         This bootconfig will be used if there is no initrd or no other
> > +         bootconfig in the initrd.
> > +
> >  choice
> >         prompt "Compiler optimization level"
> >         default CC_OPTIMIZE_FOR_PERFORMANCE
> > diff --git a/init/main.c b/init/main.c
> > index 266d61bc67b0..a5db3e36b809 100644
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -266,7 +266,7 @@ static int __init loglevel(char *str)
> >  early_param("loglevel", loglevel);
> >
> >  #ifdef CONFIG_BLK_DEV_INITRD
> > -static void * __init get_boot_config_from_initrd(u32 *_size)
> > +static void * __init get_boot_config_from_initrd(size_t *_size)
> >  {
> >         u32 size, csum;
> >         char *data;
> > @@ -412,12 +412,15 @@ static void __init setup_boot_config(void)
> >         static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
> >         const char *msg;
> >         int pos;
> > -       u32 size;
> > +       size_t size;
> >         char *data, *err;
> >         int ret;
> >
> >         /* Cut out the bootconfig data even if we have no bootconfig option */
> >         data = get_boot_config_from_initrd(&size);
> > +       /* If there is no bootconfig in initrd, try embedded one. */
> > +       if (!data)
> > +               data = xbc_get_embedded_bootconfig(&size);
> >
> >         strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
> >         err = parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0, NULL,
> > @@ -436,8 +439,8 @@ static void __init setup_boot_config(void)
> >         }
> >
> >         if (size >= XBC_DATA_MAX) {
> > -               pr_err("bootconfig size %d greater than max size %d\n",
> > -                       size, XBC_DATA_MAX);
> > +               pr_err("bootconfig size %ld greater than max size %d\n",
> > +                       (long)size, XBC_DATA_MAX);
> >                 return;
> >         }
> >
> > @@ -450,7 +453,7 @@ static void __init setup_boot_config(void)
> >                                 msg, pos);
> >         } else {
> >                 xbc_get_info(&ret, NULL);
> > -               pr_info("Load bootconfig: %d bytes %d nodes\n", size, ret);
> > +               pr_info("Load bootconfig: %ld bytes %d nodes\n", (long)size, ret);
> >                 /* keys starting with "kernel." are passed via cmdline */
> >                 extra_command_line = xbc_make_cmdline("kernel");
> >                 /* Also, "init." keys are init arguments */
> > diff --git a/lib/.gitignore b/lib/.gitignore
> > index e5e217b8307b..54596b634ecb 100644
> > --- a/lib/.gitignore
> > +++ b/lib/.gitignore
> > @@ -1,6 +1,7 @@
> >  # SPDX-License-Identifier: GPL-2.0-only
> >  /crc32table.h
> >  /crc64table.h
> > +/default.bconf
> >  /gen_crc32table
> >  /gen_crc64table
> >  /oid_registry_data.c
> > diff --git a/lib/Makefile b/lib/Makefile
> > index 08053df16c7c..2a82cc324f91 100644
> > --- a/lib/Makefile
> > +++ b/lib/Makefile
> > @@ -280,6 +280,14 @@ $(foreach file, $(libfdt_files), \
> >  lib-$(CONFIG_LIBFDT) += $(libfdt_files)
> >
> >  obj-$(CONFIG_BOOT_CONFIG) += bootconfig.o
> > +obj-$(CONFIG_EMBED_BOOT_CONFIG) += bootconfig-data.o
> > +
> > +$(obj)/bootconfig-data.o: $(obj)/default.bconf
> > +
> > +targets += default.bconf
> > +filechk_defbconf = cat $(or $(real-prereqs), /dev/null)
> > +$(obj)/default.bconf: $(CONFIG_EMBED_BOOT_CONFIG_FILE) FORCE
> > +       $(call filechk,defbconf)
> >
> >  obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
> >  obj-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o
> > diff --git a/lib/bootconfig-data.S b/lib/bootconfig-data.S
> > new file mode 100644
> > index 000000000000..df674ea7d8be
> > --- /dev/null
> > +++ b/lib/bootconfig-data.S
> > @@ -0,0 +1,11 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Embed default bootconfig in the kernel.
> > + */
> > +       .pushsection .init.data, "aw"
> > +       .global embedded_bootconfig_data
> > +embedded_bootconfig_data:
> > +       .incbin "lib/default.bconf"
> > +       .global embedded_bootconfig_data_end
> > +embedded_bootconfig_data_end:
> > +       .popsection
> 
> 
> 
> You used  .pushsection / .popsection because it was
> previously located in bootconfig.c, where there are
> functions, which should go to the ".text" section.

Oops, yes. I have made a dumb copy from the inline asm...

> Now that you split this into a separate compilation unit,
> there is only one ".init.data" section in the file.
> 
> 
>      .section  .init.data, "aw"
> 
> should be enough.

OK.

> BTW, is it reasonable/possible to make it explicitly read-only?
> 
> I have not tested this patch at all. Nor do I have enough insight.
> 
>      .section  .init.rodata, "a"
> 
> I am not sure whether this is possible or not.

Yes, it can be. The data is passed via 'const char *'.

> 
> 
> 
> Some more nits:
> 
>     default n
> 
>     default ""
> 
> are the redundant defaults in Kconfig.

Thanks for that information. Let me remove those lines. :)

> 
> 
> 
> 
> Personally, I prefer seeing the common prefix
> for options that belong to the same group,
> for example,
> 
>    CONFIG_BOOT_CONFIG
>    CONFIG_BOOT_CONFIG_EMBED
>    CONFIG_BOOT_CONFIG_EMBEDDED_FILE
> 
> 
> But, this is something like "up to you" things.

Good comment. OK, I'll change it next version.

Thank you!

> 
> 
> 
> 
> 
> 
> 
> > diff --git a/lib/bootconfig.c b/lib/bootconfig.c
> > index 74f3201ab8e5..6d30aee85ebe 100644
> > --- a/lib/bootconfig.c
> > +++ b/lib/bootconfig.c
> > @@ -12,6 +12,19 @@
> >  #include <linux/kernel.h>
> >  #include <linux/memblock.h>
> >  #include <linux/string.h>
> > +
> > +#ifdef CONFIG_EMBED_BOOT_CONFIG
> > +/* embedded_bootconfig_data is defined in bootconfig-data.S */
> > +extern __visible char embedded_bootconfig_data[];
> > +extern __visible char embedded_bootconfig_data_end[];
> > +
> > +char * __init xbc_get_embedded_bootconfig(size_t *size)
> > +{
> > +       *size = embedded_bootconfig_data_end - embedded_bootconfig_data;
> > +       return (*size) ? embedded_bootconfig_data : NULL;
> > +}
> > +#endif
> > +
> >  #else /* !__KERNEL__ */
> >  /*
> >   * NOTE: This is only for tools/bootconfig, because tools/bootconfig will
> >
> 
> 
> -- 
> Best Regards
> Masahiro Yamada


-- 
Masami Hiramatsu <mhiramat@kernel.org>

Re: [PATCH v6 3/4] bootconfig: Support embedding a bootconfig file in kernel

[Masahiro Yamada]

On Thu, Mar 31, 2022 at 3:49 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Thu, 31 Mar 2022 15:27:56 +0900
> Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> > On Thu, Mar 31, 2022 at 2:56 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
> > >
> > > This allows kernel developer to embed a default bootconfig file in
> > > the kernel instead of embedding it in the initrd. This will be good
> > > for who are using the kernel without initrd, or who needs a default
> > > bootconfigs.
> > > This needs to set two kconfigs: CONFIG_EMBED_BOOT_CONFIG=y and set
> > > the file path to CONFIG_EMBED_BOOT_CONFIG_FILE.
> > >
> > > Note that you still need 'bootconfig' command line option to load the
> > > embedded bootconfig. Also if you boot using an initrd with a different
> > > bootconfig, the kernel will use the bootconfig in the initrd, instead
> > > of the default bootconfig.
> > >
> > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> > > ---
> > >  Changes in v6:
> > >   - Split out the .incbin asm part as bootconfig-data.S according to
> > >     Masahiro's comment.
> > >  Changes in v5:
> > >   - Fix .gitignore to be sorted alphabetically.
> > >   - Make default.bconf is cleaned up correctly.
> > >   - Allow user to specify relative path to CONFIG_EMBED_BOOT_CONFIG_FILE.
> > >     (Thanks Masahiro!)
> > >  Changes in v4:
> > >   - Avoid updating the default.bconf if the file is not changed.
> > > ---
> > >  MAINTAINERS                |    1 +
> > >  include/linux/bootconfig.h |   10 ++++++++++
> > >  init/Kconfig               |   21 +++++++++++++++++++++
> > >  init/main.c                |   13 ++++++++-----
> > >  lib/.gitignore             |    1 +
> > >  lib/Makefile               |    8 ++++++++
> > >  lib/bootconfig-data.S      |   11 +++++++++++
> > >  lib/bootconfig.c           |   13 +++++++++++++
> > >  8 files changed, 73 insertions(+), 5 deletions(-)
> > >  create mode 100644 lib/bootconfig-data.S
> > >
> > > diff --git a/MAINTAINERS b/MAINTAINERS
> > > index b555a5e8704f..9b4910685412 100644
> > > --- a/MAINTAINERS
> > > +++ b/MAINTAINERS
> > > @@ -7350,6 +7350,7 @@ S:        Maintained
> > >  F:     Documentation/admin-guide/bootconfig.rst
> > >  F:     fs/proc/bootconfig.c
> > >  F:     include/linux/bootconfig.h
> > > +F:     lib/bootconfig-data.S
> > >  F:     lib/bootconfig.c
> > >  F:     tools/bootconfig/*
> > >  F:     tools/bootconfig/scripts/*
> > > diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
> > > index a4665c7ab07c..5dbda5e3e9bb 100644
> > > --- a/include/linux/bootconfig.h
> > > +++ b/include/linux/bootconfig.h
> > > @@ -289,4 +289,14 @@ int __init xbc_get_info(int *node_size, size_t *data_size);
> > >  /* XBC cleanup data structures */
> > >  void __init xbc_exit(void);
> > >
> > > +/* XBC embedded bootconfig data in kernel */
> > > +#ifdef CONFIG_EMBED_BOOT_CONFIG
> > > +char * __init xbc_get_embedded_bootconfig(size_t *size);
> > > +#else
> > > +static inline char *xbc_get_embedded_bootconfig(size_t *size)
> > > +{
> > > +       return NULL;
> > > +}
> > > +#endif
> > > +
> > >  #endif
> > > diff --git a/init/Kconfig b/init/Kconfig
> > > index 97463a33baa7..f5d14a78cfce 100644
> > > --- a/init/Kconfig
> > > +++ b/init/Kconfig
> > > @@ -1361,6 +1361,27 @@ config BOOT_CONFIG
> > >
> > >           If unsure, say Y.
> > >
> > > +config EMBED_BOOT_CONFIG
> > > +       bool "Embed bootconfig file in the kernel"
> > > +       depends on BOOT_CONFIG
> > > +       default n
> > > +       help
> > > +         Embed a bootconfig file given by EMBED_BOOT_CONFIG_FILE in the
> > > +         kernel. Usually, the bootconfig file is loaded with the initrd
> > > +         image. But if the system doesn't support initrd, this option will
> > > +         help you by embedding a bootconfig file while building the kernel.
> > > +
> > > +         If unsure, say N.
> > > +
> > > +config EMBED_BOOT_CONFIG_FILE
> > > +       string "Embedded bootconfig file path"
> > > +       default ""
> > > +       depends on EMBED_BOOT_CONFIG
> > > +       help
> > > +         Specify a bootconfig file which will be embedded to the kernel.
> > > +         This bootconfig will be used if there is no initrd or no other
> > > +         bootconfig in the initrd.
> > > +
> > >  choice
> > >         prompt "Compiler optimization level"
> > >         default CC_OPTIMIZE_FOR_PERFORMANCE
> > > diff --git a/init/main.c b/init/main.c
> > > index 266d61bc67b0..a5db3e36b809 100644
> > > --- a/init/main.c
> > > +++ b/init/main.c
> > > @@ -266,7 +266,7 @@ static int __init loglevel(char *str)
> > >  early_param("loglevel", loglevel);
> > >
> > >  #ifdef CONFIG_BLK_DEV_INITRD
> > > -static void * __init get_boot_config_from_initrd(u32 *_size)
> > > +static void * __init get_boot_config_from_initrd(size_t *_size)
> > >  {
> > >         u32 size, csum;
> > >         char *data;
> > > @@ -412,12 +412,15 @@ static void __init setup_boot_config(void)
> > >         static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
> > >         const char *msg;
> > >         int pos;
> > > -       u32 size;
> > > +       size_t size;
> > >         char *data, *err;
> > >         int ret;
> > >
> > >         /* Cut out the bootconfig data even if we have no bootconfig option */
> > >         data = get_boot_config_from_initrd(&size);
> > > +       /* If there is no bootconfig in initrd, try embedded one. */
> > > +       if (!data)
> > > +               data = xbc_get_embedded_bootconfig(&size);
> > >
> > >         strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
> > >         err = parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0, NULL,
> > > @@ -436,8 +439,8 @@ static void __init setup_boot_config(void)
> > >         }
> > >
> > >         if (size >= XBC_DATA_MAX) {
> > > -               pr_err("bootconfig size %d greater than max size %d\n",
> > > -                       size, XBC_DATA_MAX);
> > > +               pr_err("bootconfig size %ld greater than max size %d\n",
> > > +                       (long)size, XBC_DATA_MAX);
> > >                 return;
> > >         }
> > >
> > > @@ -450,7 +453,7 @@ static void __init setup_boot_config(void)
> > >                                 msg, pos);
> > >         } else {
> > >                 xbc_get_info(&ret, NULL);
> > > -               pr_info("Load bootconfig: %d bytes %d nodes\n", size, ret);
> > > +               pr_info("Load bootconfig: %ld bytes %d nodes\n", (long)size, ret);
> > >                 /* keys starting with "kernel." are passed via cmdline */
> > >                 extra_command_line = xbc_make_cmdline("kernel");
> > >                 /* Also, "init." keys are init arguments */
> > > diff --git a/lib/.gitignore b/lib/.gitignore
> > > index e5e217b8307b..54596b634ecb 100644
> > > --- a/lib/.gitignore
> > > +++ b/lib/.gitignore
> > > @@ -1,6 +1,7 @@
> > >  # SPDX-License-Identifier: GPL-2.0-only
> > >  /crc32table.h
> > >  /crc64table.h
> > > +/default.bconf
> > >  /gen_crc32table
> > >  /gen_crc64table
> > >  /oid_registry_data.c
> > > diff --git a/lib/Makefile b/lib/Makefile
> > > index 08053df16c7c..2a82cc324f91 100644
> > > --- a/lib/Makefile
> > > +++ b/lib/Makefile
> > > @@ -280,6 +280,14 @@ $(foreach file, $(libfdt_files), \
> > >  lib-$(CONFIG_LIBFDT) += $(libfdt_files)
> > >
> > >  obj-$(CONFIG_BOOT_CONFIG) += bootconfig.o
> > > +obj-$(CONFIG_EMBED_BOOT_CONFIG) += bootconfig-data.o
> > > +
> > > +$(obj)/bootconfig-data.o: $(obj)/default.bconf
> > > +
> > > +targets += default.bconf
> > > +filechk_defbconf = cat $(or $(real-prereqs), /dev/null)
> > > +$(obj)/default.bconf: $(CONFIG_EMBED_BOOT_CONFIG_FILE) FORCE
> > > +       $(call filechk,defbconf)
> > >
> > >  obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
> > >  obj-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o
> > > diff --git a/lib/bootconfig-data.S b/lib/bootconfig-data.S
> > > new file mode 100644
> > > index 000000000000..df674ea7d8be
> > > --- /dev/null
> > > +++ b/lib/bootconfig-data.S
> > > @@ -0,0 +1,11 @@
> > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > +/*
> > > + * Embed default bootconfig in the kernel.
> > > + */
> > > +       .pushsection .init.data, "aw"
> > > +       .global embedded_bootconfig_data
> > > +embedded_bootconfig_data:
> > > +       .incbin "lib/default.bconf"
> > > +       .global embedded_bootconfig_data_end
> > > +embedded_bootconfig_data_end:
> > > +       .popsection
> >
> >
> >
> > You used  .pushsection / .popsection because it was
> > previously located in bootconfig.c, where there are
> > functions, which should go to the ".text" section.
>
> Oops, yes. I have made a dumb copy from the inline asm...
>
> > Now that you split this into a separate compilation unit,
> > there is only one ".init.data" section in the file.
> >
> >
> >      .section  .init.data, "aw"
> >
> > should be enough.
>
> OK.
>
> > BTW, is it reasonable/possible to make it explicitly read-only?
> >
> > I have not tested this patch at all. Nor do I have enough insight.
> >
> >      .section  .init.rodata, "a"
> >
> > I am not sure whether this is possible or not.
>
> Yes, it can be. The data is passed via 'const char *'.

But, you didn't add "const" in the C code:

extern __visible char embedded_bootconfig_data[];
extern __visible char embedded_bootconfig_data_end[];


Is it possible to use "const char" ?



-- 
Best Regards
Masahiro Yamada

Re: [PATCH v6 3/4] bootconfig: Support embedding a bootconfig file in kernel

[Masami Hiramatsu]

On Thu, 31 Mar 2022 15:54:40 +0900
Masahiro Yamada <masahiroy@kernel.org> wrote:

> On Thu, Mar 31, 2022 at 3:49 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
> >
> > On Thu, 31 Mar 2022 15:27:56 +0900
> > Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > > On Thu, Mar 31, 2022 at 2:56 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
> > > >
> > > > This allows kernel developer to embed a default bootconfig file in
> > > > the kernel instead of embedding it in the initrd. This will be good
> > > > for who are using the kernel without initrd, or who needs a default
> > > > bootconfigs.
> > > > This needs to set two kconfigs: CONFIG_EMBED_BOOT_CONFIG=y and set
> > > > the file path to CONFIG_EMBED_BOOT_CONFIG_FILE.
> > > >
> > > > Note that you still need 'bootconfig' command line option to load the
> > > > embedded bootconfig. Also if you boot using an initrd with a different
> > > > bootconfig, the kernel will use the bootconfig in the initrd, instead
> > > > of the default bootconfig.
> > > >
> > > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> > > > ---
> > > >  Changes in v6:
> > > >   - Split out the .incbin asm part as bootconfig-data.S according to
> > > >     Masahiro's comment.
> > > >  Changes in v5:
> > > >   - Fix .gitignore to be sorted alphabetically.
> > > >   - Make default.bconf is cleaned up correctly.
> > > >   - Allow user to specify relative path to CONFIG_EMBED_BOOT_CONFIG_FILE.
> > > >     (Thanks Masahiro!)
> > > >  Changes in v4:
> > > >   - Avoid updating the default.bconf if the file is not changed.
> > > > ---
> > > >  MAINTAINERS                |    1 +
> > > >  include/linux/bootconfig.h |   10 ++++++++++
> > > >  init/Kconfig               |   21 +++++++++++++++++++++
> > > >  init/main.c                |   13 ++++++++-----
> > > >  lib/.gitignore             |    1 +
> > > >  lib/Makefile               |    8 ++++++++
> > > >  lib/bootconfig-data.S      |   11 +++++++++++
> > > >  lib/bootconfig.c           |   13 +++++++++++++
> > > >  8 files changed, 73 insertions(+), 5 deletions(-)
> > > >  create mode 100644 lib/bootconfig-data.S
> > > >
> > > > diff --git a/MAINTAINERS b/MAINTAINERS
> > > > index b555a5e8704f..9b4910685412 100644
> > > > --- a/MAINTAINERS
> > > > +++ b/MAINTAINERS
> > > > @@ -7350,6 +7350,7 @@ S:        Maintained
> > > >  F:     Documentation/admin-guide/bootconfig.rst
> > > >  F:     fs/proc/bootconfig.c
> > > >  F:     include/linux/bootconfig.h
> > > > +F:     lib/bootconfig-data.S
> > > >  F:     lib/bootconfig.c
> > > >  F:     tools/bootconfig/*
> > > >  F:     tools/bootconfig/scripts/*
> > > > diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
> > > > index a4665c7ab07c..5dbda5e3e9bb 100644
> > > > --- a/include/linux/bootconfig.h
> > > > +++ b/include/linux/bootconfig.h
> > > > @@ -289,4 +289,14 @@ int __init xbc_get_info(int *node_size, size_t *data_size);
> > > >  /* XBC cleanup data structures */
> > > >  void __init xbc_exit(void);
> > > >
> > > > +/* XBC embedded bootconfig data in kernel */
> > > > +#ifdef CONFIG_EMBED_BOOT_CONFIG
> > > > +char * __init xbc_get_embedded_bootconfig(size_t *size);
> > > > +#else
> > > > +static inline char *xbc_get_embedded_bootconfig(size_t *size)
> > > > +{
> > > > +       return NULL;
> > > > +}
> > > > +#endif
> > > > +
> > > >  #endif
> > > > diff --git a/init/Kconfig b/init/Kconfig
> > > > index 97463a33baa7..f5d14a78cfce 100644
> > > > --- a/init/Kconfig
> > > > +++ b/init/Kconfig
> > > > @@ -1361,6 +1361,27 @@ config BOOT_CONFIG
> > > >
> > > >           If unsure, say Y.
> > > >
> > > > +config EMBED_BOOT_CONFIG
> > > > +       bool "Embed bootconfig file in the kernel"
> > > > +       depends on BOOT_CONFIG
> > > > +       default n
> > > > +       help
> > > > +         Embed a bootconfig file given by EMBED_BOOT_CONFIG_FILE in the
> > > > +         kernel. Usually, the bootconfig file is loaded with the initrd
> > > > +         image. But if the system doesn't support initrd, this option will
> > > > +         help you by embedding a bootconfig file while building the kernel.
> > > > +
> > > > +         If unsure, say N.
> > > > +
> > > > +config EMBED_BOOT_CONFIG_FILE
> > > > +       string "Embedded bootconfig file path"
> > > > +       default ""
> > > > +       depends on EMBED_BOOT_CONFIG
> > > > +       help
> > > > +         Specify a bootconfig file which will be embedded to the kernel.
> > > > +         This bootconfig will be used if there is no initrd or no other
> > > > +         bootconfig in the initrd.
> > > > +
> > > >  choice
> > > >         prompt "Compiler optimization level"
> > > >         default CC_OPTIMIZE_FOR_PERFORMANCE
> > > > diff --git a/init/main.c b/init/main.c
> > > > index 266d61bc67b0..a5db3e36b809 100644
> > > > --- a/init/main.c
> > > > +++ b/init/main.c
> > > > @@ -266,7 +266,7 @@ static int __init loglevel(char *str)
> > > >  early_param("loglevel", loglevel);
> > > >
> > > >  #ifdef CONFIG_BLK_DEV_INITRD
> > > > -static void * __init get_boot_config_from_initrd(u32 *_size)
> > > > +static void * __init get_boot_config_from_initrd(size_t *_size)
> > > >  {
> > > >         u32 size, csum;
> > > >         char *data;
> > > > @@ -412,12 +412,15 @@ static void __init setup_boot_config(void)
> > > >         static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
> > > >         const char *msg;
> > > >         int pos;
> > > > -       u32 size;
> > > > +       size_t size;
> > > >         char *data, *err;
> > > >         int ret;
> > > >
> > > >         /* Cut out the bootconfig data even if we have no bootconfig option */
> > > >         data = get_boot_config_from_initrd(&size);
> > > > +       /* If there is no bootconfig in initrd, try embedded one. */
> > > > +       if (!data)
> > > > +               data = xbc_get_embedded_bootconfig(&size);
> > > >
> > > >         strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
> > > >         err = parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0, NULL,
> > > > @@ -436,8 +439,8 @@ static void __init setup_boot_config(void)
> > > >         }
> > > >
> > > >         if (size >= XBC_DATA_MAX) {
> > > > -               pr_err("bootconfig size %d greater than max size %d\n",
> > > > -                       size, XBC_DATA_MAX);
> > > > +               pr_err("bootconfig size %ld greater than max size %d\n",
> > > > +                       (long)size, XBC_DATA_MAX);
> > > >                 return;
> > > >         }
> > > >
> > > > @@ -450,7 +453,7 @@ static void __init setup_boot_config(void)
> > > >                                 msg, pos);
> > > >         } else {
> > > >                 xbc_get_info(&ret, NULL);
> > > > -               pr_info("Load bootconfig: %d bytes %d nodes\n", size, ret);
> > > > +               pr_info("Load bootconfig: %ld bytes %d nodes\n", (long)size, ret);
> > > >                 /* keys starting with "kernel." are passed via cmdline */
> > > >                 extra_command_line = xbc_make_cmdline("kernel");
> > > >                 /* Also, "init." keys are init arguments */
> > > > diff --git a/lib/.gitignore b/lib/.gitignore
> > > > index e5e217b8307b..54596b634ecb 100644
> > > > --- a/lib/.gitignore
> > > > +++ b/lib/.gitignore
> > > > @@ -1,6 +1,7 @@
> > > >  # SPDX-License-Identifier: GPL-2.0-only
> > > >  /crc32table.h
> > > >  /crc64table.h
> > > > +/default.bconf
> > > >  /gen_crc32table
> > > >  /gen_crc64table
> > > >  /oid_registry_data.c
> > > > diff --git a/lib/Makefile b/lib/Makefile
> > > > index 08053df16c7c..2a82cc324f91 100644
> > > > --- a/lib/Makefile
> > > > +++ b/lib/Makefile
> > > > @@ -280,6 +280,14 @@ $(foreach file, $(libfdt_files), \
> > > >  lib-$(CONFIG_LIBFDT) += $(libfdt_files)
> > > >
> > > >  obj-$(CONFIG_BOOT_CONFIG) += bootconfig.o
> > > > +obj-$(CONFIG_EMBED_BOOT_CONFIG) += bootconfig-data.o
> > > > +
> > > > +$(obj)/bootconfig-data.o: $(obj)/default.bconf
> > > > +
> > > > +targets += default.bconf
> > > > +filechk_defbconf = cat $(or $(real-prereqs), /dev/null)
> > > > +$(obj)/default.bconf: $(CONFIG_EMBED_BOOT_CONFIG_FILE) FORCE
> > > > +       $(call filechk,defbconf)
> > > >
> > > >  obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
> > > >  obj-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o
> > > > diff --git a/lib/bootconfig-data.S b/lib/bootconfig-data.S
> > > > new file mode 100644
> > > > index 000000000000..df674ea7d8be
> > > > --- /dev/null
> > > > +++ b/lib/bootconfig-data.S
> > > > @@ -0,0 +1,11 @@
> > > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > > +/*
> > > > + * Embed default bootconfig in the kernel.
> > > > + */
> > > > +       .pushsection .init.data, "aw"
> > > > +       .global embedded_bootconfig_data
> > > > +embedded_bootconfig_data:
> > > > +       .incbin "lib/default.bconf"
> > > > +       .global embedded_bootconfig_data_end
> > > > +embedded_bootconfig_data_end:
> > > > +       .popsection
> > >
> > >
> > >
> > > You used  .pushsection / .popsection because it was
> > > previously located in bootconfig.c, where there are
> > > functions, which should go to the ".text" section.
> >
> > Oops, yes. I have made a dumb copy from the inline asm...
> >
> > > Now that you split this into a separate compilation unit,
> > > there is only one ".init.data" section in the file.
> > >
> > >
> > >      .section  .init.data, "aw"
> > >
> > > should be enough.
> >
> > OK.
> >
> > > BTW, is it reasonable/possible to make it explicitly read-only?
> > >
> > > I have not tested this patch at all. Nor do I have enough insight.
> > >
> > >      .section  .init.rodata, "a"
> > >
> > > I am not sure whether this is possible or not.
> >
> > Yes, it can be. The data is passed via 'const char *'.
> 
> But, you didn't add "const" in the C code:
> 
> extern __visible char embedded_bootconfig_data[];
> extern __visible char embedded_bootconfig_data_end[];
> 
> 
> Is it possible to use "const char" ?

Yes, I need to update C part too, and that is not a problem. :)

Thank you!

> 
> 
> 
> -- 
> Best Regards
> Masahiro Yamada


-- 
Masami Hiramatsu <mhiramat@kernel.org>

[PATCH v6 4/4] docs: bootconfig: Add how to embed the bootconfig into kernel

[Masami Hiramatsu]

Add a description how to embed the bootconfig file into kernel.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Changes in v5:
  - Update CONFIG_EMBED_BOOT_CONFIG_FILE which can accept relative path.
 Changes in v3:
  - Fix typos.
 Changes in v2:
  - Corrected the text accoding to Randy's suggestion.
  - Do not reccomend to use relative path for CONFIG_EMBED_BOOT_CONFIG_FILE.
---
 Documentation/admin-guide/bootconfig.rst |   31 +++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst
index a1860fc0ca88..83a2a0cc9afa 100644
--- a/Documentation/admin-guide/bootconfig.rst
+++ b/Documentation/admin-guide/bootconfig.rst
@@ -158,9 +158,15 @@ Each key-value pair is shown in each line with following style::
 Boot Kernel With a Boot Config
 ==============================
 
-Since the boot configuration file is loaded with initrd, it will be added
-to the end of the initrd (initramfs) image file with padding, size,
-checksum and 12-byte magic word as below.
+There are two options to boot the kernel with bootconfig: attaching the
+bootconfig to the initrd image or embedding it in the kernel itself.
+
+Attaching a Boot Config to Initrd
+---------------------------------
+
+Since the boot configuration file is loaded with initrd by default,
+it will be added to the end of the initrd (initramfs) image file with
+padding, size, checksum and 12-byte magic word as below.
 
 [initrd][bootconfig][padding][size(le32)][checksum(le32)][#BOOTCONFIG\n]
 
@@ -196,6 +202,25 @@ To remove the config from the image, you can use -d option as below::
 Then add "bootconfig" on the normal kernel command line to tell the
 kernel to look for the bootconfig at the end of the initrd file.
 
+Embedding a Boot Config into Kernel
+-----------------------------------
+
+If you can not use initrd, you can also embed the bootconfig file in the
+kernel by Kconfig options. In this case, you need to recompile the kernel
+with the following configs::
+
+ CONFIG_EMBED_BOOT_CONFIG=y
+ CONFIG_EMBED_BOOT_CONFIG_FILE="/PATH/TO/BOOTCONFIG/FILE"
+
+``CONFIG_EMBED_BOOT_CONFIG_FILE`` requires an absolute path or a relative
+path to the bootconfig file from source tree or object tree.
+The kernel will embed it as the default bootconfig.
+
+Just as when attaching the bootconfig to the initrd, you need ``bootconfig``
+option on the kernel command line to enable the embedded bootconfig.
+
+Note that even if you set this option, you can override the embedded
+bootconfig by another bootconfig which attached to the initrd.
 
 Kernel parameters via Boot Config
 =================================