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<think>
Okay, I need to classify this bug report into one of three categories: instruction, syscall, or runtime. Let me read through the problem description again to understand what's going on.
The issue is about inconsistent behavior in the probe_access() function between full-system and linux-user modes in QEMU. In full-system mode, when the TLB_MMIO flag is set, probe_access returns NULL, which leads to using a slow-path for memory access (cpu_stb_mmuidx_ra) and correctly injecting mem_cbs. However, in linux-user mode, it returns the correct address instead of NULL, causing the fast-path (memset) to be used without injecting callbacks.
The problem affects RISC-V's helper_cbo_zero() function, which handles zeroing memory. The inconsistency leads to different behaviors depending on the QEMU mode. To fix this, probe_access() should return NULL in both modes when TLB_MMIO is set, ensuring consistent handling of memory access and callbacks.
Now, looking at the categories:
- Instruction: This would be if the bug was about a specific CPU instruction being handled incorrectly.
- Syscall: If it involved errors with system calls.
- Runtime: Errors that occur during runtime but aren't related to instructions or syscalls.
This issue isn't directly about an instruction or a syscall; rather, it's about how memory accesses are handled at runtime. The inconsistency in probe_access affects the execution flow and memory callbacks during runtime operations. Therefore, it falls under the runtime category.
</think>
runtime
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