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Date:   Sat, 12 Mar 2022 15:53:58 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Padmanabha Srinivasaiah <treasure4paddy@gmail.com>
Cc:     rostedt@goodmis.org, linux-kernel@vger.kernel.org
Subject: Re: tracing : bootconfig : Early boot config for non intrd systems
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Hello Padmanabha,

On Wed, 9 Mar 2022 20:06:51 +0100
Padmanabha Srinivasaiah <treasure4paddy@gmail.com> wrote:

> On Wed, Mar 09, 2022 at 05:01:24PM +0900, Masami Hiramatsu wrote:
> > On Tue, 8 Mar 2022 18:48:29 +0100
> > Padmanabha Srinivasaiah <treasure4paddy@gmail.com> wrote:
> > 
> > > Hello Masami Hiramatsu,
> > > 
> > > On Tue, Mar 08, 2022 at 04:36:00PM +0900, Masami Hiramatsu wrote:
> > > > Hello Padmanabha,
> > > > 
> > > > On Mon, 7 Mar 2022 19:40:11 +0100
> > > > Padmanabha Srinivasaiah <treasure4paddy@gmail.com> wrote:
> > > > 
> > > > > Hello Masami Hiramatsu,
> > > > > 
> > > > > Thanks for detailed explanation on boot time tracing using early boot configuration file.
> > > > > https://linuxfoundation.org/wp-content/uploads/boottrace-LF-live-2021-update.pdf
> > > > > 
> > > > > Also for https://lwn.net/Articles/806002/.
> > > > > 
> > > > > Latter link also states we can embed boot config into the kernel image for non intrd based system.
> > > > 
> > > > Ah, that was an original plan, but since no one interested in, I didn't implement it.
> > > > So we still need the initrd for bootconfig.
> > > >
> > > Ok.
> > > > > 
> > > > > I tried searching mailing lists not able to find pointer for same.
> > > > > 
> > > > > A hint/pointer on how-to will be very helpful. 
> > > > 
> > > > BTW, what is your problem, could you share your use-case?
> > > > 
> > > 
> > > I have hetrogenous system which donot use intrd.
> > > 
> > > The use-case is to capture __system wide__ event based tracing for
> > > boot-up sequence, which also covers early stage of default init programs
> > > used.
> > > 
> > > As buffer size is limited, will have hand-picked events set configured.
> > 
> > Hm, so I guess you will boot linux from your custom bootloader (or binary loader on sub processor?).
> >
> Yes, customised implemation which loads linux. 
> 
> > Can you even try to add a dummy initrd? or are you OK to rebuild kernel for embedding the bootconfig data?
> Yes, re-building the kernel image to appended bootconfig data is feasable option.
> 

OK, please try below patch. You can embed your bootconfig in the kernel via
CONFIG_EMBED_BOOT_CONFIG_FILE.


From 7478a8fbfe4669ee61fcb12b85b36d7e36f992ba Mon Sep 17 00:00:00 2001
From: Masami Hiramatsu <mhiramat@kernel.org>
Date: Sat, 12 Mar 2022 14:59:30 +0900
Subject: [PATCH] bootconfig: Support embedding a bootconfig file in kernel

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 2 options: CONFIG_EMBED_BOOT_CONFIG=y and set the file
name to CONFIG_EMBED_BOOT_CONFIG_FILE.
Note that you still need 'bootconfig' command line option to load the
embedded bootconfig. And if you boot with the initrd which has another
bootconfig, the kernel will use the bootconfig in the initrd, instead
of embedding one.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 include/linux/bootconfig.h | 10 ++++++++++
 init/Kconfig               | 19 +++++++++++++++++++
 init/main.c                | 25 +++++++++++++------------
 lib/bootconfig.c           | 23 +++++++++++++++++++++++
 4 files changed, 65 insertions(+), 12 deletions(-)

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 e9119bf54b1f..1b736ac7f90d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1357,6 +1357,25 @@ 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.
+
 choice
 	prompt "Compiler optimization level"
 	default CC_OPTIMIZE_FOR_PERFORMANCE
diff --git a/init/main.c b/init/main.c
index 65fa2e41a9c0..f371610bc008 100644
--- a/init/main.c
+++ b/init/main.c
@@ -265,7 +265,7 @@ 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(size_t *_size)
 {
 	u32 size, csum;
 	char *data;
@@ -299,12 +299,15 @@ 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;
 }
@@ -408,12 +411,15 @@ static void __init setup_boot_config(void)
 	static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
 	const char *msg;
 	int pos;
-	u32 size, csum;
+	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, &csum);
+	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,
@@ -432,16 +438,11 @@ static void __init setup_boot_config(void)
 	}
 
 	if (size >= XBC_DATA_MAX) {
-		pr_err("bootconfig size %d greater than max size %d\n",
+		pr_err("bootconfig size %ld greater than max size %d\n",
 			size, XBC_DATA_MAX);
 		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)
@@ -451,7 +452,7 @@ 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", 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/bootconfig.c b/lib/bootconfig.c
index 74f3201ab8e5..bf84f5838c08 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -12,6 +12,29 @@
 #include <linux/kernel.h>
 #include <linux/memblock.h>
 #include <linux/string.h>
+
+#ifdef CONFIG_EMBED_BOOT_CONFIG
+asm (
+"	.pushsection .init.data, \"aw\"			\n"
+"	.global embedded_bootconfig_data		\n"
+"embedded_bootconfig_data:				\n"
+"	.incbin \"" CONFIG_EMBED_BOOT_CONFIG_FILE "\"	\n"
+"	.global embedded_bootconfig_data_end		\n"
+"embedded_bootconfig_data_end:				\n"
+"	.popsection					\n"
+);
+
+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 embedded_bootconfig_data;
+}
+
+#endif
+
 #else /* !__KERNEL__ */
 /*
  * NOTE: This is only for tools/bootconfig, because tools/bootconfig will
-- 
2.25.1


-- 
Masami Hiramatsu <mhiramat@kernel.org>