Re: Debug grub scripts without rebooting into grub shell.

[Hongyi Zhao]

On Sun, Jul 9, 2023 at 2:49 PM Andrei Borzenkov <arvidjaar@gmail.com> wrote:
>
> On 09.07.2023 09:33, Hongyi Zhao wrote:
> > On Sun, Jul 9, 2023 at 1:13 PM Andrei Borzenkov <arvidjaar@gmail.com> wrote:
> >>
> >> On 09.07.2023 03:21, Hongyi Zhao wrote:
> >>> On Sat, Jul 8, 2023 at 9:53 PM Andrei Borzenkov <arvidjaar@gmail.com> 
> >>> wrote:
> >>>>
> >>>> On 08.07.2023 14:58, Hongyi Zhao wrote:
> >>>>> Hi here,
> >>>>>
> >>>>> Are there some convenient methods to debug grub scripts without
> >>>>> rebooting into grub shell?
> >>>>>
> >>>>
> >>>> You may try grub-emu which emulates grub.
> >>>
> >>> I tried, but it seems that grub-emu doesn't meet my requirement as
> >>> described below.
> >>>
> >>> I want to debug the grubx64.efi created by the following command:
> >>>
> >>
> >> If you want to debug grubx64.efi, then you of course need to load it
> >> either on real hardware or in VM. But you can debug scripts used by
> >> grubx64.efi using grub-emu by setting up suitable simulated environment.
> >> There are clear limitations (scripts cannot load and start any kernel).
> >
> > Then, how to access the real hard disk devices and partitions? I can
> > only see the following devices via grub-emu:
> >
>
> You create device.map and give names hd0, hd1, ... to your devices.

See below:

werner@X10DAi:~$ sudo grub-mkdevicemap -n
werner@X10DAi:~$ cat /boot/grub/device.map
(hd0)    /dev/disk/by-id/nvme-SAMSUNG_MZVL22T0HBLB-00B00_S677NF0R503706
(hd1)    /dev/disk/by-id/ata-WDC_WDS100T2B0A-00SM50_191533467906

Now, I see the following devices in grub-emu:

grub> ls
(proc) (hd0) (hd1) (host)

But how to access the corresponding partitions on these devices?

> > grub> ls
> > (proc) (host)
> >
> > Best,
> > Zhao
> >
> >>> $ grub-mkstandalone -O x86_64-efi -o grubx64.efi --modules='lvm fat
> >>> ntfs part_msdos part_gpt ext2 btrfs probe regexp search configfile'
> >>> boot/grub/grub.cfg=./grub.cfg
> >>>
> >>> The content of the ./grub.cfg is as follows:
> >>>
> >>> $ egrep -v '^[ ]*(#|$)' grub.cfg
> >>> regexp -s __cmdpath_efi '^\(([^,]+)' "$cmdpath"
> >>> export __cmdpath_efi
> >>> for file in ($__cmdpath_efi,*)/multibootusb.git/grub.cfg; do
> >>>     if regexp -s __root '^(\([^*]+\))' "$file"; then
> >>>       set __prefix=$__root/multibootusb.git
> >>>       export __root
> >>>       export __prefix
> >>>       configfile $__prefix/grub.cfg
> >>>       break
> >>>     fi
> >>> done
> >>>
> >>> The files' layout is as follows:
> >>>
> >>> $ tree .
> >>> .
> >>> ├── grub.cfg
> >>> ├── grub-mkstandalone.sh
> >>> ├── grubx64.efi
> >>> └── iso
> >>>       ├── deepin-desktop-community-23-Beta-amd64.iso
> >>>       ├── rescatux-0.74.iso
> >>>       ├── supergrub2-2.06s1-beta2-multiarch-CD.iso
> >>>       ├── systemrescue-10.01-amd64.iso
> >>>       ├── ubuntu-23.04-desktop-amd64.iso
> >>>       └── ubuntukylin-23.04-desktop-amd64.iso
> >>>
> >>> 1 directory, 9 files
> >>>
> >>> Regards,
> >>> Zhao