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CentOS 8 supports GCC 8.2.1, so I recommend sticking with the same version for to guarantee ABI compatibility. You may install GCC from any provider such as ARM, Linaro , or Xilinx ( Vitis), etc. The link below will pull the aarch64 cross compiler 8.2.1 binaries from ARM.

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Once the cross compiler is downloaded, extract it to a location of your choice and add the bin directory to your PATH. For example, I installed it in $HOME/bin and prepended PATH in my “.bashrc” file.

PATH="$HOME/bin:$HOME/bin/gcc-arm-8.2-2019.01-x86_64-aarch64-linux-gnu/bin:$PATH"

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Copy the generated “boot.bin” into the deploy directory we created earlier.

$ cp tmp/deploy/images/zcu102-zynqmp/BOOT-zcu102-zynqmp.bin $COS_BUILD/deploy/efi/boot.bin

Build the Kernel

This build section walks through two builds of the kernel. The first is a bootstrap kernel, which is a straight forward make build. The second uses the official boostrap kernel does not rely on any kernel modules to mount the final root filesystem. The second kernel is built with the CentOS RPM build system for CentOS. The This build system pulls directly from the CentOS kernel repository which also includes patches, kernel configurations and utility build scripts.

Clone the CentOS 8 Kernel Source

Here we are going to clone “centos-git-common” which includes utility build scripts for CentOS and the CentOS “kernel” repository which includes source and spec files for the RPM build. The “get_sources.sh” script will fetch the kernel source tarball.

$ cd $COS_BUILD/rpmbuild
$ git clone https://git.centos.org/centos-git-common.git
$ git clone https://git.centos.org/rpms/kernel.git
$ cd kernel
$ git checkout -b kernel-4.18.0-147.3.1.el8_1.xlnx imports/c8/kernel-4.18.0-147.3.1.el8_1
$ ../centos-git-common/get_sources.sh

As a good measure, lets install any additional package dependencies required by the SPEC file that we may have missed.

sudo dnf builddep SPECS/kernel.spec

Build a Bootstrap Kernel

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Build a Bootstrap Kernel

Because the installed CentOS kernel image may not include some critical configurations required for Zynq UltraScale+, you may need to build a bootstrap kernel. Once we boot the bootstrap kernel, we can formally install the kernel RPMS which will installs the newly configured kernel and updates the initrd and GRUB configuration.

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$ cp BUILDROOT/kernel-4.18.0-147.3.1.el8.xlnx.aarch64/boot/dtb-4.18.0-147.3.1.el8.xlnx.aarch64/xilinx/zynqmp-zcu102-rev1.0.dtb $COS_BUILD/deploy/efi/dtb/xilinx/

cp RPMS/aarch64/kernel-4.18.0-147.3.1.el8.xlnx.aarch64.rpm RPMS/aarch64/kernel-core-4.18.0-147.3.1.el8.xlnx.aarch64.rpm \
RPMS/aarch64/kernel-modules-4.18.0-147.3.1.el8.xlnx.aarch64.rpm $COS_BUILD/*.rpm $COS_BUILD/deploy/boot/

Install UEFI and Kernel on a Preinstalled CentOS Disk Image

We will start with a install the bootloader and kernel on a prebuilt CentOS 8 Stream raw disk image of a CentOS server as the basis for our system.

$ cd $COS_BUILD/images
#$ copy the qcow2 image here

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wget https://cloud.centos.org/centos/8-stream/aarch64/images/CentOS-Stream-GenericCloud-8-20200113.0.aarch64.qcow2

Change the root password with “virt-customize” to “zynqmp” or a password of your choice.

$ virt-customize -a CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.qcow2 --root-password password:zynqmppassword password:zynqmp
[   0.0] Examining the guest ...
[  33.4] Setting a random seed
[  33.7] Setting the machine ID in /etc/machine-id
[  33.8] Setting passwords
[  51.3] Finishing off

The installed file is a QCOW2 (QEMU copy-on-write) virtual disk, so we need to convert it to a raw disk image.

$ qemu-img convert CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.qcow2 CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.raw

Now lets examine the partitions in this disk image. You will see there are 3 partitions. The first is the EFI System Partition (ESP) which is a FAT formatted partition. The second partition is an EXT4 a Linux formatted partition. The third partition is an LVM root filesystem.

$ fdisk -l CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.raw
Disk CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.raw: 710 GiB, 751619276810737418240 bytes, 1468006420971520 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: E51C2C48079AB561-87F2A1E1-419D4340-BA13A744-687E3930A160C041B93E2E67

Device                                                 Start      End  Sectors  Size Type
CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.raw1    2048  1230847  1228800  600M EFI System
CentOS-8Stream-aarch64GenericCloud-19058-dvd1.raw2 1230848  3327999  2097152    1G Linux filesystem
CentOS-8-aarch64-1905-dvd1.raw3 3328000 14678015 11350016  5.4G Linux LVM20200113.0.aarch64.raw2 1230848 17614847 16384000  7.8G Linu

The first thing we note is that “Disklabel type” is set to “gpt”. However, Zynq UltraScale+ only support MBR partitioned disks, so we need to convert from GPT to MBR with “sgdisk”.

$ sgdisk -m 1:2:3 CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.raw 
Warning: The kernel is still using the old partition table.
The new table will be used at the next reboot or after you
run partprobe(8) or kpartx(8)
GPT data structures destroyed! You may now partition the disk using fdisk or
other utilities.

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$ sfdisk -A CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.raw 1
The bootable flag on partition 1 is enabled now.

The partition table has been altered.
Syncing disks.

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$ fdisk -l CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.raw
Disk CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.raw: 710 GiB, 751619276810737418240 bytes, 1468006420971520 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device                                               Boot   Start      End  Sectors  Size Id Type
CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.raw1 *       2048  1230847  1228800  600M ef EFI (FAT-12/16/32)
CentOS-8-aarch64-1905-dvd1.raw2      1230848  3327999  2097152    1G 83 Linux
CentOSStream-GenericCloud-8-aarch64-1905-dvd1.raw320200113.0.aarch64.raw2      33280001230848 1467801517614847 1135001616384000  57.4G8G 8e83 Linux LVMLinu

We need to setup the map devices for the raw disk image we prepared earlier. Mount the first two partitions on “efi” and “boot” “rootfs” respectively.

$ cd $COS_BUILD/images
$ sudo kpartx -va CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.raw 
add map loop0p1 (253:123): 0 1228800 linear 7:40 2048
add map loop0p2 (253:134): 0 209715216384000 linear 7:40 1230848
add map loop0p3 (253:14): 0 11350016 linear 7:4 3328000
$ sudo mount /dev/mapper/loop0p1 efi
$ sudo mount /dev/mapper/loop0p2 bootrootfs

The Zynq UltraScale+ boot ROM will search for “boot.bin” on the first partition. The boot ROM will load FSBL and PMU firmware. FSBL will in turn load u-boot. U-boot acting as the UEFI firmware will search the current partition for the corresponding board DTB file and pass it to the EFI bootloader through the EFI configuration table. If it doesn’t find one, it will pass its own DTB to the EFI bootloader. However, this DTB may not be compatible with your kernel version, so I recommend using the DTB built with the kernel. So let's install the UEFI firmware (boot.bin) and ZCU102 DTB as shown below from the deploy directory.

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Since we are not using UEFI secure boot, we want to boot GRUB directly. So we need to will replace shim (bootaa64.efi) with GRUB (grubaa64.efi).

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grubaa64.efi).

$ sudo cp efi/EFI/centos/grubaa64.efi efi/EFI/BOOT/bootaa64.efi

Next lets install the bootstrap kernel and kernel RPM packages into the BOOT directory.

$ sudo cp efi../EFIdeploy/centosboot/grubaa64.efi* efirootfs/EFIboot/BOOT/bootaa64.efi

Next lets install the bootstrap kernel and kernel RPM packages into the BOOT directory.

$ sudo cp ../deploy/boot/* boot/

Since we are installing on a cloud image, we need to disable the cloud-init to make it look more like a standard distro. If you are installing on a disk image generated from an ISO, this step should be skipped.

$ sudo touch rootfs/etc/cloud/cloud-init.disabled

Finally, let’s unmount the partitions and cleanup the device mappings.

$ sudo umount efi
$ sudo umount bootrootfs
$ sudo kpartx -d CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.raw
loop deleted : /dev/loop0

Now the raw disk image is ready to write to the SD card. With the CD SD card plugged into your CentOS machine, note the device node of your card (/dev/sdX) and install the image as shown below.

$ sudo dd if=CentOS-Stream-GenericCloud-8-aarch64-1905-dvd120200113.0.aarch64.raw of=/dev/sdX bs=4M iflag=fullblock oflag=direct status=progress; sync

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