On 11/14/23 at 08:03am, Joe Perches wrote:

On Tue, 2023-11-14 at 23:32 +0800, Baoquan He wrote:

quoted

When specifying 'kexec -c -d', kexec_load interface will print loading
information, e.g the regions where kernel/initrd/purgatory/cmdline
are put, the memmap passed to 2nd kernel taken as system RAM ranges,
and printing all contents of struct kexec_segment, etc. These are
very helpful for analyzing or positioning what's happening when
kexec/kdump itself failed. The debugging printing for kexec_load
interface is made in user space utility kexec-tools.

Whereas, with kexec_file_load interface, 'kexec -s -d' print nothing.
Because kexec_file code is mostly implemented in kernel space, and the
debugging printing functionality is missed. It's not convenient when
debugging kexec/kdump loading and jumping with kexec_file_load
interface.

Now add KEXEC_FILE_DEBUG to kexec_file flag to control the debugging
message printing. And add global variable kexec_file_dbg_print and
macro kexec_dprintk() to facilitate the printing.

This is a preparation, later kexec_dprintk() will be used to replace the
existing pr_debug(). Once 'kexec -s -d' is specified, it will print out
kexec/kdump loading information. If '-d' is not specified, it regresses
to pr_debug().

Not quite as pr_debug is completely eliminated with
zero object size when DEBUG is not #defined.

Now the object size will be larger and contain the
formats in .text.

Ah, I didn't realize that. Thanks for telling. I didn't take pr_info()
and pr_debug because I want to avoid printing the pr_fmt() string in
each file.

[]

quoted

diff --git a/include/linux/kexec.h b/include/linux/kexec.h

[]

quoted

@@ -264,6 +264,18 @@ arch_kexec_apply_relocations(struct purgatory_info *pi, Elf_Shdr *section,
 	return -ENOEXEC;
 }
 #endif
+
+extern bool kexec_file_dbg_print;
+
+#define kexec_dprintk(fmt, args...)			\
+	do {						\
+		if (kexec_file_dbg_print)		\
+			printk(KERN_INFO fmt, ##args);	\
+		else					\
+			printk(KERN_DEBUG fmt, ##args);	\
+	} while (0)
+
+

I don't know how many of these printks exist and if
overall object size matters but using

Not too much because they are spread in different arch.

#define kexec_dprintkfmt, ...)					\
	printk("%s" fmt,					\
	       kexec_file_dbg_print ? KERN_INFO : KERN_DEBUG,	\
	       ##__VA_ARGS__)

should reduce overall object size by eliminating the
mostly duplicated format in .text which differs only
by the KERN_<PREFIX>

Sure, the new one looks great to me, I will update code to take it.
Thanks a lot for your great suggestion.

Thanks
Baoquan


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