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<think>
Okay, I need to classify this bug report as either 'user' or 'system'. Let me read through the information provided.
The user is working on VSX support in libVPX and is using QEMU for testing. They modified a function from vec_sub to vec_subs in loopfilter_vsx.c and encountered an Illegal Instruction error when running under QEMU-ppc64le. However, it works fine on a POWER9 machine.
The bug occurs during the execution of the application inside QEMU. The backtrace shows that it's crashing within the CPU loop of QEMU, specifically in sigsuspend. This suggests that the issue is with how QEMU emulates certain instructions or handles signals when running user-space code.
Since the problem arises when executing their own code (libVPX), which runs correctly on real hardware but not under QEMU, it's likely a user-mode emulation issue. QEMU's user mode (like qemu-ppc64le) translates and executes guest instructions in a user space process without requiring kernel-level changes or device handling.
Therefore, the bug is related to how QEMU handles the translation of the modified instruction vec_subs, causing an illegal instruction error. This falls under user-mode emulation because it's about executing the guest application within QEMU's user environment.
</think>
user
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