There are some cases when it is needed to see the full log of Linux kernel panic.
But it often can't be done through the regular terminal in display.
I thought that it should be done through the COM-port, but can't figure out:
How can I do that?
What is the reason of working well through COM-port, but not through terminal in my display?
UPD: I use debian-based custom Linux (4.9 kernel) with HDMI-display.
Related: How to get a Linux panic output to a USB serial console when system has also a display adapter
Simple direct connected console / VTY use the graphics card to convert character bytes (0 - 255) into display character cells. 80x25 is a common format. This is very simple and not hard for a crashing kernel to manage. Just copy some memory around.
The graphical console is more complicated because the kernel now has to locate the font bitmap for a character and copy the bitmap onto the display. It also needs to handle scrolling with more memory copies, or IOCTL calls into the graphics driver, etc.
A console running in a Gnome or KDE GUI session is very complicated. The kernel isn't involved in drawing it at all and doesn't know how.
The more complex the output process is, the less likely that a kernel that is already crashing can manage it successfully.
Serial port output is once again very simple. A buffered UART makes it a bit more complicated, but if a crashing kernel wants to ignore that and simply output bytes at a 9,600 line rate, any serial port will work with that without needing buffers or interrupt management.