Re: Debug grub scripts without rebooting into grub shell.

[Andrei Borzenkov]

On 09.07.2023 10:00, Hongyi Zhao wrote:
> 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?

Did you try to load partition driver?

> > > 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