Compile a correct Linux kernel

Clone a Linux tree and run make ARCH=arm defconfig to make a generic kernel configuration suited for qemu. Now edit the kernel configuration (.config) and add the following lines at the bottom:

Now run make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- -j$(nproc) to compile the kernel. If you get asked about anything, just press enter to use the standard value.

Copy the output zImage (arch/arm/boot/zImage) to efi/boot/bootarm.efi on your EFI partition folder in your qemu directory.

Prepare GDB for debugging

Install

Run sudo apt-get install gdb-multiarch to install GDB on Ubuntu. gdb-mutliarch is required because normal gdb package doesn't have support for ARM.

Run

Open up the terminal you want GDB to run in, and change directory to your Linux compilation directory. Then run gdb-multiarch vmlinux., it will open GDB you and you can now connect to a target with target remote localhost:1234. At this point GDB will wait for qemu to start. After that you can now debug with qemu, there are tutorials online to show you how to do this.

Run qemu

Go to the directory where your qemu files are located, start qemu as described in , only change is that you need to add a -s parameter, this lets qemu know that it starts a GDB server.

Create configuration files

The following steps have to be performed in your Linux source directory.

Create tasks.json

Create a file called tasks.json in the directory .vscode and paste the following contents into it:

See for the documentation about the tasks.json format

Create launch.json

Create a file called launch.json in the directory .vscode and paste the following contents into it: Use IntelliSense to learn about possible attributes. Hover to view descriptions of existing attributes. For more information, visit:

Create c_cpp_properties.json

Create a file called c_cpp_properties.json in the directory .vscode and paste the following contents into it:

Debug

Press F5 to start debugging. The following steps will be performed:

• Compile Kernel

• Copy zImage to qemu EFI partition

• Launch qemu

The following keys are important:

• F9 for creating a breakpoint

• F10 for going a step forward

• F11 for stepping into a function

Emulating a arm32 UEFI device is useful for developing Linux and debugging it.

In the GDB Debugging page you can find instructions on how to compile Linux for this virtual machine.

Compile OVMF for qemu

Install required packages

Run the following commands to install the required packages.

You will need other stuff too, but that is probably already installed. (e.g. git)

Download source

You need the source code of edk2 and acpica.

Compile OVMF

Go to your source directory and run the following commands.

Your output OVMF firmware file for qemu is$WORKSPACE/Build/ArmVirtQemu-ARM/RELEASEGCC5/FV/QEMU_EFI.fd

Setup qemu files and run it

Create a directory, where you want your files to be in. Put your QEMU_EFI.fd firmware file in this directory, compiled in the previous section. Now run the following commands to create some disk images:

Now create a directory named boot. This will be your EFI partition. You can now easily place your EFI files in there.

Run qemu

To start your virtual machine run the following command, and make sure qemu-system-arm is installed.

This will run qemu with 4 virtual CPU cores. They are Coretx-A15 cores. Used because it works.

Premade files

The following ZIP includes all files setup in their proper location. In addition its EFI partition folder has a UEFI shell in it. To run it either execute the run.sh file or enter the command described in .

References

Links where the above compiling information is from:

Surface RT 1

@Leander's trial and fail

Note to members of the gitbook: I don't know if it is useful to make this person-specific.

#001

This hangs at without supplying device tree with dtb= If device tree is supplied, cpuidle complains at printed. [ 0.000000] platform regulatory.0: Direct firmware load for regulatory.db failed with error -2 [ 0.000000] cfg80211: failed to load regulatory.db

#002

Changed:CONFIG_CFG80211=n [ 0.000000] platform regulatory.0: Direct firmware load for regulatory.db failed with error -2 [ 0.000000] cfg80211: failed to load regulatory.db This is issue doesn't exist anymore, it just freezes at [ 0.000000] Freeing unused kernel memory: 1024K

Note the line, clock should be 100kHz[ 0.000000] sched_clock: 32 bits at 100 Hz, resolution 10000000ns, wraps every 21474836475000000ns

[ 0.000000] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled [ 0.000000] Warning: unable to open an initial console. It looks like it's using some serial and then is unable to open a console. -> No device tree so it doesn't know /dev/ttyS0 (UART-A)

#003

CONFIG_FB_EFI=y CONFIG_CMDLINE="console=ttyS0,115200 console=tty0 earlyprintk initcall_debug sched_debug lpj=10000"

It booted, then disabled uart and printed to the screen. Log only contains print from uart. Stuck at the same line.

#004

CONFIG_CMDLINE="console=ttyS0,115200 console=tty0 earlycon earlyprintk initcall_debug sched_debug lpj=10000"

Log should be the same apart from the cmdline. Again, it displayed to display, so log doesn't include that output.

#005

CONFIG_CMDLINE="console=ttyS0,115200 earlycon earlyprintk initcall_debug sched_debug lpj=10000"

Screen with a cursor, all output on uart. But because there is no device tree, no console from initrd.

#006

Nothing changed in config. Only added device tree.

Kernel panic: [ 0.000000] Unable to handle kernel NULL pointer dereference at virtual address 00000010Has to do with cpuidle. You can also see complaints about a bad device tree.

#007

Only device tree edits.

Screen has no cursor anymore, only backlight is turned on. You can't print something on it with echo hello >> /dev/fb0 or echo hello >> /dev/tty0

Successful boot to Buildroot.

Note: Log has a lot of entries two times.

#008

CONFIG_VGA_ARB=n CONFIG_TEGRA_HOST1X=n CONFIG_DRM=n

No different screen behaviour.

Log has some commands at the bottom.

#009

No config changed. Only device tree edits. Added nodes to it until dtc didn't complain about anything.

Some strange screen behaviour.

[ 0.000000] tegra20-cpufreq tegra20-cpufreq: operating points not found [ 0.000000] tegra20-cpufreq tegra20-cpufreq: please update your device tree Looks like some cpu frequency nodes have to be added to device tree.

#010

Only device tree edits.

Screen still doesn't work.

Boots fine to Buildroot. Log has commands at the bottom.

#011

CONFIG_CMDLINE="console=ttyS0,115200 console=tty0 earlyprintk initcall_debug sched_debug lpj=10000"

Found out that screen works, but it gets cleared when Busybox (from ramdisk) starts. At least I think at that point it gets cleared, not 100% sure.

#012

CONFIG_CMDLINE="console=ttyS0,115200 earlyprintk initcall_debug sched_debug lpj=10000"

Minimal device tree with sd-card+emmc+uart, it includes tegra30.dtsi

No display output with this command line, but you get log output when adding console=tty0, but afterwards it stops around when Busybox takes over.

#013

Added a raspberry pi rootfs. Specifying root= option with efi shell

Display stops working after the line [ 251.431349] tegra-devfreq 6000c800.actmon: Failed to get emc clock

Log contains output from rootfs.

#014

CONFIG_EFI_STUB=y CONFIG_EFI=y CONFIG_CMDLINE="console=ttyS0,115200n8 earlyprintk initcall_debug sched_debug lpj=10000 boot_delay=50" CONFIG_CMDLINE_EXTEND=y CONFIG_SMP=n CONFIG_CACHE_L2X0=n CONFIG_EARLY_PRINTK=y CONFIG_DEBUG_TEGRA_UART=y CONFIG_TEGRA_DEBUG_UARTA=y CONFIG_BOOT_PRINTK_DELAY=y

CONFIG_BOOT_PRINTK_DELAY=y and boot_delay=50(cmdline) are necessary so mmc driver gets loaded early enough.

Log contains a few commands from rootfs.

#015

I'm not sure what changed.

Working display with booted raspberry pi os!

Surface RT 2

Issues

• PMIC regulators don't work.