Re: [PATCH 1/7] kexec_file: add kexec_file flag to control debug printing

Joe Perches
2023-11-14T16:09:23Z

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

[]
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
[]
> @@ -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

#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>