Okay, so I'm looking at this bug report regarding QEMU/TCG not handling certain exceptions correctly when dealing with RSP and RBP registers in non-canonical addresses. The issue is that instead of generating a #SS exception (which should happen when the stack pointer is involved), it's incorrectly raising a #GP exception. The user provided some context, showing that under KVM or native hardware, accessing memory via RSP or RBP with non-canonical addresses triggers an #SS exception. However, under QEMU using TCG, both access via RAX and RSP/RBP result in #GP exceptions, which is incorrect. Looking at the code snippet provided, it seems that currently, when a non-canonical address is detected, the code always sets the exception to EXCP0D_GPF (#GP). The user's note mentions that they think QEMU should instead check if the fault was due to RSP or RBP and then trigger #SS. The Intel SDM specifies that stack faults (#SS) occur when a non-canonical address is used with the stack pointer, but the AMD manual explicitly includes any instruction using RSP or RBP as a base register. This discrepancy suggests that QEMU's current handling doesn't align with the expected behavior for these registers. Now, considering whether this issue is related to user-mode or system-mode: - User-mode refers to processes running without special privileges, typically dealing with application-level issues. - System-mode involves higher privilege levels, including kernel operations and device drivers. The problem here seems to affect how exceptions are generated based on the context of memory accesses. Since RSP and RBP are often used in both user and kernel contexts (though more commonly in user for stack frames), the handling is likely relevant across different modes. However, looking at the test case provided by the user, it's a selftest within Xen, which suggests that this issue affects system-level operations. The Xen hypervisor relies on correct exception handling to maintain stability and security between domains. If exceptions are not correctly generated when RSP or RBP access non-canonical addresses in the hypervisor context, it could lead to incorrect behavior or crashes. Additionally, since the problem causes a selftest failure in Xen, which is system-level software managing virtual machines, this indicates that the bug impacts how QEMU emulates CPU exceptions in a way critical to higher-privilege operations. Therefore, this isn't just about user applications but affects the underlying system infrastructure managed by Xen. In summary, while the issue involves general-purpose registers and memory access, its impact on hypervisor-level testing suggests it's a system-mode related bug. system