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<think>
Okay, so I'm trying to figure out whether this bug in QEMU is related to user-mode or system-mode issues. The user is compiling QEMU 1.1.0 on Ubuntu 13.04 and encountering undefined reference errors when linking qemu-ga. The errors point to functions like timer_gettime, timer_settime, etc., which are part of the POSIX timer API.
First, I remember that in C programming, if you use functions from a library that's not linked during compilation, you get these "undefined reference" errors. So here, it seems the linker isn't finding the real-time library (librt), which contains those timer functions. The user mentioned they tried adding '-lrt' but didn't know where to put it in the Makefile.
Now, thinking about QEMU's architecture: QEMU can run in two main modes—user mode and system mode. User-mode emulation allows running programs compiled for another CPU on your current one without virtualizing hardware. System-mode emulates an entire computer, including hardware devices.
The error occurs during the linking of qemu-ga, which is the guest agent used for communication between the host and the VM. Guest agents are typically part of system-mode QEMU because they interact with the virtualized environment, managing resources like CPU ticks and timers.
Looking at the functions causing issues: timer_create, timer_settime, etc., these are used to manage high-resolution timers, which are essential for accurate timekeeping in a virtualized system. These functions require linking against librt, as the user noted. Without this library, the linker can't resolve those symbols.
So why is this happening? It's likely that the Makefile for QEMU 1.1.0 doesn't include '-lrt' when compiling qemu-ga. Maybe newer versions of QEMU automatically handle this, but in older versions like 1.1.0, it wasn't included. The fact that the user can compile later versions without issues suggests that perhaps the build process was updated to link against librt in those releases.
Considering system-mode versus user-mode: In system-mode, QEMU deals with more low-level tasks, including emulating timers and handling real-time operations, which would require these timer functions. User-mode might not need such precise timing as it's more about executing binaries without full hardware emulation.
Therefore, since the issue arises in a part of QEMU that's used for system emulation (qemu-ga is part of the system-mode setup), this bug is related to system-mode.
</think>
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