I'm working with some embedded system.

I'm looking for the way to log all console messages to file.
In my embedded system, all messages are displayed on console such as
boot loader message, kernel message ("printk"), application message.

I want to log these all message to file located in my embadded system. as many as possible. (I think bootloader's message can't be captured. it's ok.)
klogd and syslogd is good but not in my system.
and redirection is restricted to application case.
host-side serial application (tera term or minicom) can do but not what i'm expecting because I have too many devices.

is there any good way to capture all messages sent to console?
kernel can be modified if necessary.

please tell me your advice.