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<think>
Okay, so I'm looking at this problem where a test program is behaving differently on native CPU versus QEMU. The issue seems to revolve around how certain return instructions handle non-canonical IP addresses.
The user provided three programs using RET, LRET, and IRETQ. In each case, the expected behavior is that when these instructions try to return to a non-canonical address (like 0x1234567812345678), they should cause a segmentation fault because the IP is invalid.
On a native CPU, when IRETQ is executed with this bad IP, it correctly segfaults and points to the failed IRET instruction. However, in QEMU, instead of failing during the return, it seems like the instruction succeeds, but then trying to fetch instructions from that non-canonical address causes the exception. This difference means QEMU isn't emulating the CPU behavior accurately.
The question is whether this bug falls under user-mode or system-mode emulation. User-mode typically deals with application-level operations and doesn't require special privileges. System-mode involves higher-privilege levels, like kernel operations, device drivers, etc.
RET, LRET, and IRETQ are all instructions that affect the flow of execution by modifying the stack and IP. In x86, these can operate in different privilege levels. For example, IRET is used for returning from interrupts and can involve changing privilege levels if it's a far return (like when using LRET with a segment override). However, in this test case, it looks like they're being used in user-mode since the programs are compiled without standard libraries, suggesting they run at the lowest privilege level.
The issue arises because QEMU isn't correctly handling how these instructions should fail when encountering invalid IPs. Since the problem occurs during normal program execution and doesn't involve kernel or device-level operations, it seems to be a user-mode emulation bug.
Therefore, this report is related to user-mode.
</think>
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