Okay, let's see. The user is encountering an issue with QEMU where the ioctl call for USBDEVFS_BULK returns -1 with EFAULT when using qemu-arm-static, but works fine with qemu-aarch64-static. They're on a 64-bit Intel laptop. First, I need to figure out what's going on here. The problem is specific to the static ARM emulator versus the AArch64 one. The error is EFAULT, which means "Bad address," typically indicating that the user-space pointer passed to a system call isn't valid. Looking at the code snippet: they're setting up a usbdevfs_bulktransfer structure, filling in the endpoint, length, data pointer, and timeout. Then they call ioctl with the USBDEVFS_BULK command. The error occurs in the ioctl call. Now, the key here is that this works on aarch64 but not on arm. Since USBDEVFS_BULK is a legacy interface (now replaced by libusb and the usbfs is deprecated), maybe there's a difference in how QEMU handles the ioctl for different architectures. The EFAULT suggests that the kernel (or QEMU's emulation of the kernel) is trying to access the user-provided buffer and finds an invalid address. Since QEMU is emulating the ARM system, perhaps there's a discrepancy in how user pointers are handled between the 32-bit and 64-bit emulations. In the case of qemu-arm-static, it's emulating a 32-bit ARM system. When using ioctl, the kernel expects the pointer (Bulk.data) to be within the user space that it can access. If the data pointer is from the host's address space (which is 64-bit), but QEMU is trying to emulate a 32-bit ARM system, the address might not be valid in the emulated context. In contrast, qemu-aarch64-static is emulating a 64-bit ARM system. If the host is 64-bit as well, the pointers might be compatible, allowing the ioctl to work correctly. This seems to be a problem related to how QEMU handles system calls, specifically the ioctl, when translating between the host's address space and the guest's. The EFAULT is likely because the emulated process (32-bit ARM) can't access the 64-bit host's memory address. So, since the issue is with the system call (ioctl) and how the addresses are handled in the context of QEMU's emulation, this falls under the syscall category. The problem isn't with the instruction itself but with how the system call is processed, particularly the handling of user-space pointers across different architectures. syscall