The build-qemu script provides lots of useful features and is an easy way to run U-Boot under QEMU with an OS, with or without video, etc. Now in Concept it is possible to pass a boot command!
The -b/–bootcmd option creates a special ‘file’ within QEMU that contains the requested command. Then U-Boot uses an event in main.c to check for that file and read it. The command is then executed instead of the autoboot command. In effect, it provides a way to control what U-Boot does when it starts up.
Possible uses may include setting the bootmeth order to boot using extlinux instead of EFI.
Note that this does not affect the preboot command.
The main patch is the addition of a new EVT_BOOTCMD event which is emitted in main_loop() before starting the main CLI loop. Under the hood, QEMU provides the information in its internal filesystem, the the opt/u-boot/bootcmd file. You can see this using the ‘qfw’ command:
$ ./scripts/build-qemu -a x86 -rs -b 'echo hi'
U-Boot Concept SPL 2025.10
Trying to boot from SPI
U-Boot Concept 2025.10
CPU: QEMU Virtual CPU version 2.5+
DRAM: 512 MiB
Core: 19 devices, 12 uclasses, devicetree: separate
Loading Environment from FAT... ** Bad device specification virtio 0 **
Model: QEMU x86 (Q35)
Net: eth0: virtio-net#0
Hit any key to stop autoboot: 0
hi
=> qfw list
Addr Size Sel Name
-------- -------- --- ------------
0 0 20 bios-geometry
0 0 21 bootorder
1ec21000 14 22 etc/acpi/rsdp
1ec21040 20000 23 etc/acpi/tables
0 4 24 etc/boot-fail-wait
0 28 25 etc/e820
0 18 26 etc/smbios/smbios-anchor
0 13b 27 etc/smbios/smbios-tables
0 1 28 etc/smi/features-ok
0 8 29 etc/smi/requested-features
0 8 2a etc/smi/supported-features
0 6 2b etc/system-states
0 1000 2c etc/table-loader
0 0 2d etc/tpm/log
0 2400 2e genroms/kvmvapic.bin
0 7 2f opt/u-boot/bootcmd
=>
For now this option is only supported on x86, but ARM support should land in the next few weeks.
The build-efi script also supports this option for the app, but it is implemented in a completely different way. It creates an environment file on the FAT filesystem which U-Boot can read when it starts up. A later series provides this feature which is has also landed in Concept.
The ability to pass information from the host is a useful feature in QEMU. Keep it in mind if you are working in an emulation environment!
