Okay, let's try to figure out how to categorize this bug report. The problem is about signals not being delivered properly when using pselect in a program run under QEMU. The user says that when running the test case via qemu, the signal handler isn't called even though the pselect is interrupted. First, I need to recall what pselect does. From what I remember, pselect is similar to select but it allows specifying a signal mask to be set atomically with the select call. This is useful for handling signals without race conditions. The program in question blocks SIGUSR1, then uses pselect with an empty signal mask, which should unblock it temporarily. When the signal is sent during pselect, the handler should be called upon returning. The issue here is that when running under QEMU, the signal isn't caught. The user mentions that QEMU's -strace shows the signal isn't received, but QEMU's own strace shows it's delivered. So the signal is being delivered to QEMU but not to the guest program. Now, considering the categories: instruction, syscall, or runtime. An instruction category bug would be related to incorrect CPU instructions being executed, maybe emulation issues. But this seems to be about system call handling. The syscall category is about errors in system calls. However, the problem here isn't that the system call itself is incorrect, but rather how QEMU handles the delivery of signals during the pselect system call. Runtime errors are other issues during program execution not covered by the other categories. However, since the problem is specifically about how QEMU handles the pselect system call and signal delivery, this seems more like a syscall handling issue in QEMU. Wait, but the problem is that the signal isn't being passed through correctly. The pselect system call in the guest is expecting to handle the signal, but QEMU isn't delivering it properly. That would be a problem in how QEMU emulates the system call behavior, particularly regarding signal handling. Since pselect is a system call, and QEMU's emulation of it isn't correctly handling the signal mask or delivery, this would fall under the syscall category. Therefore, the correct category is syscall. syscall