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<think>
Okay, let's see. The user is asking why qemu-x86_64 fails when trying to call unshare with CLONE_NEWUSER. The problem is that when they run the command through QEMU, it gives an "Invalid argument" error, but when they run it directly, it works.
First, I need to understand what unshare does. The unshare command with --user creates a new user namespace. This is a Linux kernel feature that allows processes to have their own view of user IDs. So, when they run it normally, it works, but under QEMU, it doesn't.
Now, QEMU is an emulator. When you run a binary with QEMU, it's emulating the CPU and other hardware. But user namespaces are a kernel feature. So, if QEMU is emulating an x86_64 environment, but the underlying host kernel might not support certain features required for user namespaces.
Wait, but the user is running QEMU on the same system where the command works normally. So maybe QEMU isn't handling the unshare system call correctly. The unshare system call is a Linux syscall. When the program runs under QEMU, it's QEMU's job to correctly translate the x86 instructions into the host's architecture, but in this case, it's x86_64 on the same machine. Wait, maybe the QEMU system emulator vs user-mode?
Wait, there's QEMU system mode and user mode. The qemu-x86_64 here is probably the user-mode emulator. But when you run a binary with qemu-x86_64, it's executing the x86_64 binary in user mode, which should still use the host's kernel system calls. However, user namespaces require certain kernel features. If the host kernel doesn't support user namespaces, or if QEMU is not properly passing the syscall through, that could cause an issue.
But the user is able to run unshare directly, so the host kernel does support it. Therefore, the problem must be that QEMU is not handling the unshare syscall correctly when emulating the x86_64 user-space. Maybe QEMU's user-mode emulation doesn't fully support certain syscalls, or there's a bug in how it handles CLONE_NEWUSER.
So, this seems like a syscall issue. The problem is that QEMU isn't correctly handling the unshare system call, leading to an invalid argument error. The user is using QEMU to run the binary, and the error occurs because QEMU isn't passing the syscall correctly to the host kernel. Therefore, the category would be syscall.
</think>
syscall
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