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I am currently trying to debug the boot sequence of Xen, and past a certain point, the only way to do it is over a serial connection. Now, on the laptop I'm using there exists no serial port nor an ExpressCard slot. It also does not support any variant of serial-over-lan. I know that generally, systems during boot do not recognize USB to serial adapters, thus not outputting anything to them. My question is, how to determine that this is indeed the case? For example, doing dmesg | grep uart outputs nothing, but when I do dmesg | grep serial I get the following:

[    0.778940] usbcore: registered new interface driver usbserial_generic
[    0.778944] usbserial: USB Serial support registered for generic

This is what gave me some hope that I might be able to get output over an USB-to-serial adapter.

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This is possible, but you need to have the usb serial driver compiled into the kernel. It must not be a module. Most likely this will involve recompilling of the kernel.

https://www.kernel.org/doc/html/v4.15/admin-guide/serial-console.html

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