I am currently working on emulating an ARMv9 architecture with SME (Scalable Matrix Extension) using QEMU on an x86 host running Ubuntu 20.04. I am using the qemu-aarch64 binary to run my tests in user mode, but I am facing an issue when trying to specify the SME vector length.
From the QEMU documentation (https://qemu.readthedocs.io/en/v9.0.2/system/arm/cpu-features.html#sme-cpu-properties), I understand that the sme_default_vector_length parameter needs to be configured in /proc/sys/abi/ to control the SME vector length. However, when I check my system, I do not see this parameter in /proc/sys/abi/.
My question is:
How can I specify or modify the SME vector length while running QEMU in user mode for ARMv9? Is there a way to control this setting in a user-mode QEMU execution, or is this feature limited to system-mode emulation? Any help or guidance would be greatly appreciated. Thank you in advance!
You have misinterpreted that part of the documentation. It is not telling you that you must configure these vector lengths in /proc/sys/abi/. It is telling you that the QEMU options for configuring the vector lengths use the same values as you would use if you were on a real Arm system and configuring the vector length on the real kernel (which you do via /proc/sys/abi), and that it has the same behaviour as if you'd done that on a real Arm Linux kernel.
For QEMU, you specify the default vector length using the CPU properties sve-default-vector-length and sme-default-vector-length (e.g. -cpu max,sve-default-vector-length=128).