On 2024-10-25, Pascal Hambourg wrote: > On 24/10/2024 at 22:04, Diederik de Haas wrote: >> On Thu Oct 24, 2024 at 9:08 PM CEST, Holger Wansing wrote: >>> >>> here you have a device|installation, which has the legacy_boot flag >>> installed, but it did not work|boot despite of this. And you changed that >>> legacy_boot flag into a boot flag, and that made the problem go away? >>> (so the device boots fine). > > IIUC, it booted successfully after setting the legacy_boot flag on the > /boot partition. And it still booted successfully after setting the > boot/esp flag and removing the legacy_boot flag.
I think there are several things that u-boot treats as bootable ... https://source.denx.de/u-boot/u-boot/-/blob/3fbc657669591ca893613f14d42e07069b7d56cd/doc/develop/distro.rst?plain=1#L38-62 Distros simply need to install the boot configuration files (see next section) in an ext2/3/4 or FAT partition, mark the partition bootable (via the MBR bootable flag, or GPT legacy_bios_bootable attribute), and U-Boot (or any other bootloader) will find those boot files and execute them. This is conceptually identical to creating a grub2 configuration file on a desktop PC. Note that in the absence of any partition that is explicitly marked bootable, U-Boot falls back to searching the first valid partition of a disk for boot configuration files. Other bootloaders are recommended to do the same, since I believe that partition table bootable flags aren't so commonly used outside the realm of x86 PCs. So this is both relevent if using u-boot to using various boot methods, such as extlinux.conf style configuration produced by u-boot-menu or boot.scr produced by flash-kernel... but also it might be relevent if you are using u-boot as your EFI implementation to load grub-efi. I am not entirely sure the above documentation is exhaustive; I seem to recall u-boot also treating the ESP/EFI partition as bootable, but that may be because various other flags get set at the same time... though I have used ESP/EFI partitions as /boot with u-boot before without any EFI implementation. A very cursory search of u-boot source code did not reveal any additional ways u-boot might treat a partition as "bootable", though the documentation I quoted from is kind of the old style "distro" boot vs. the newer "bootstd" which I am less familiar with... Mixed feelings about leaving the first 16MB unpartitioned vs. specifying some partition for it that has some special flag set. Creating a partition and marking it with MBR boot or legacy_bios_boot might trip up u-boot if it does not contain the extlinux/boot.scr/efi stuff it is expecting. live well, vagrant
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