Okay, I need to figure out how to classify this bug report. The user provided several C code snippets that use inline assembly instructions. When these codes are compiled and run under QEMU, they trigger an illegal instruction error (signal 4). However, when executed on a real machine, the programs work fine. Looking at the code examples, each uses specific x86-64 SIMD instructions like `psignw`, `pmulhrsw`, etc. These are part of SSE and AVX instruction sets. The problem arises because QEMU's version (2.7.0) might not support all these instructions or has issues emulating them correctly. The user provided information about their system: they're running Ubuntu with a 3.13 kernel, using GCC 4.8.4 and QEMU 2.7.0. The real machine probably supports the necessary instruction sets, but QEMU's emulation is lacking, causing the error. So, this issue isn't related to syscalls or runtime errors in general. It's specifically about certain instructions not being handled properly by QEMU. Therefore, it falls under the "instruction" category. The bug report describes issues with specific x86-64 instructions not being correctly emulated by QEMU 2.7.0, leading to illegal instruction errors when running programs that use those instructions. Real hardware supports these instructions, but QEMU's emulation is faulty. **Answer:** instruction