Issues booting from bare metal

[markusbkk]

Describe your bug or error

When booting from a Ventoy (latest version) prepared USB flash drive, there's no progress past "loading /boot/kernel.elf".
The screen remains totally blank.

Under Qemu, it works as expected.

Is there any way to debug the kernel during boot-up?

Hardware

Lenovo Thinkpad E535

AMD A4-4300M CPU
4GB RAM
500GB Samsung 840 EVO

I'm booting from a small 4GB flash drive, turned off secure boot and enabled both UEFI and legacy BIOS (with legacy BIOS being given the preference).

Go Version

1.16.15

Relevant log output

No response

[icexin]

eggos use grub as the bootloader, so you should see the grub ui after booting, if not, may something wrong with grub.

[icexin]

Also setting a higher timeout in boot/grub.cfg may help you to stay in grub ui

[markusbkk]

eggos use grub as the bootloader, so you should see the grub ui after booting, if not, may something wrong with grub.

I do get the GRUB UI. After I wait or hit enter, it tells me that it's loading the kernel.elf and then there's a big sea of black.

[markusbkk]

I don't suppose there's an easy way to log any kernel issues and have them written to a file on the flash drive?

[icexin]

the only way for PC is writing to screen with https://wiki.osdev.org/Printing_To_Screen, the breakpoints can be set in following order:

• The c boot loader https://github.com/icexin/eggos/tree/main/boot
• The go entry https://github.com/icexin/eggos/blob/78b167e4f34946b41fc39fe444bfc44133ab1ecb/kernel/asm_amd64.s#L8C29-L8C29

[icexin]

You may try writing UART if available :)

[markusbkk]

Thanks. Will look at it later, after I've ruled out that it's an issue with Ventoy.

[markusbkk]

@icexin Could this be the issue?

Keep in mind that this way of writing to video memory will only work if the screen has been correctly set up for 80x25 video mode (which is mode 03). You can do this either by initializing every VGA register manually, or by calling the Set Video Mode service of the BIOS Int10h while you're still in real mode (in your bootsector, for instance). Most BIOS's do that initialization for you, but some other (mainly on laptops) do not