Booting in EFI (and legacy CSM bios) mode not possible on older Apple EFI based systems
Hi there,
I noticed with gparted-live-1.0.0-3 the problem that on older Apple EFI based systems no successful booting is possible.
Booting in native EFI mode with "safe VGA" is working until X server. Then it crashes also, - regardless which resolution or color depth is used in manual X configuration.
The following error message is displayed several times during booting-up in (any) EFI mode:
[drm:radeon_init [radeon]] *ERROR* No UMS support in radeon module!
This indicates that something is going wrong with the Radeon driver. After intensive research I found the information that at Apple's EFI implementation the vbios is "not being exposed in EFI mode": https://forum.artixlinux.org/index.php/topic,586.msg4591.html#msg4591
So the Radeon driver has simply no vbios information available, - and therefore it fails. On Apple EFI systems, the vbios seems to be available only for a short time during the power on, "IIRC, the vbios on macs is only available in (EFI) boot services so it's likely gone by the time the OS (or GRUB) is loaded": https://bugs.freedesktop.org/show_bug.cgi?id=26891
There seems the exist a chance to get around this with the rEFInd boot-loader. In conjunction with GRUB it seems to be definitively NOT possible.
A hack to extract the vbios: https://bugs.freedesktop.org/attachment.cgi?id=33766&action=edit
Some interesting information regarding EFI stub and kernel compatibility: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1649326
Enable native EFI boot on older Apple EFI firmware: https://forum.artixlinux.org/index.php/topic,586.msg4608.html#msg4608
However, my final workaround can be found at the following link: https://bugs.launchpad.net/ubuntu-cdimage/+bug/1298894/comments/16
The mentioned C program from Thomas Schmitt removes more or less any EFI related information in the boot sector of the CD / DVD image. As a result, the CD / DVD is booting always in legacy CSM bios mode. This works great on ANY Apple EFI based system. I can confirm this for several Linux based distros like CentOS 7, GPparted, clonezilla, and the KDE neon Live DVD.
Without that "remastering" the system hangs with the following message displayed:
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1.
2.
Select CD-ROM Boot Type :
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Well, a drawback is that in legacy CSM mode certain (from Apple) EFI-only enabled and accessible system features (like keyboard backlight, AHCI S-ATA mode, etc.) are not present. However, for a Live CD based Linux system like GParted this is not a big issue.