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RE: Questions about grub_video_set_mode()

From: Dexuan Cui
Subject: RE: Questions about grub_video_set_mode()
Date: Sat, 11 Aug 2018 01:14:19 +0000

> From: Paul Menzel <address@hidden>
> Sent: Thursday, August 9, 2018 12:30 AM
> ...
> > 4. What's the best way to debug grub_video_set_mode()?
> >   grub_dprintf() can't output anything in this function.
> Why? Because the display is not working?
Hi Paul,
Actually it works -- it looks somehow I was careless... I'm sorry!

> > Does grub support remote debugging via network?
> > I know gdb can debug grub in Qemu, but here the issue looks like
> > Hyper-V specific.
> If Hyper-V can emulate a serial port, then this should be one way to
> go. Something like below for `/etc/default/grub`.
> GRUB_TERMINAL="console serial"
> GRUB_SERIAL_COMMAND="serial --unit=0 --speed=115200"
This serial port works very well for me. Thanks for sharing the trick!

> Paul

About my original questions, it looks grub is doing right here: sometimes
the VM can have "linux_gfx_mode=text", and if this happens, it looks correct
for grub to set grub_video_adapter_active to NULL.

However, I believe the line
grub_memset (&mode_info, 0, sizeof (mode_info)); 
is unnecessary, and the commnt before the line 
grub_video_adapter_active = NULL;
may seem incorrect. Of course, this is harmless.

-- Dexuan

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