Software⏱️ 4 min read📅 2026-06-11

How to Fix: Get Illegal Instruction error when booting Linux in VirtualBox, works fine when booted directly

VirtualBox Linux boot error with invalid opcode

Quick Answer: Try disabling CPU-specific optimizations in CFLAGS to resolve the issue.

📋 Table of Contents

  1. 🔍 Why This Happens
  2. 🚀 How to Resolve This Issue
  3. ✨ Wrapping Up

The 'Get Illegal Instruction error' issue occurs when booting Linux in VirtualBox, but not directly on the host machine. This error message is usually caused by the lack of CPU-specific optimizations during compilation, which can lead to a mismatch between the compiled code and the actual processor architecture. In this guide, we will explore possible causes for this error and provide steps to troubleshoot and resolve the issue.

This issue can be frustrating because it prevents Linux from booting in VirtualBox, which is a common use case for many users. However, by following the steps outlined in this guide, you should be able to identify and fix the root cause of the problem.

🔍 Why This Happens

  • The primary reason for this error is that the compiled pixman library lacks CPU-specific optimizations, which can lead to a mismatch between the compiled code and the actual processor architecture. This is likely due to the compiler flags used during compilation.
  • Another possible cause could be a hardware-related issue with VirtualBox or the host machine's CPU. However, since the error occurs in libpixman-1.so.0, which is a user-mode library, it is less likely that this is a hardware-related problem.

🚀 How to Resolve This Issue

Recompiling pixman without -march

  1. Step 1: Open a terminal and navigate to the directory where you compiled pixman. Run the command `gcc --version` to verify that the compiler is using the correct flags.
  2. Step 2: Run the command `make clean` to remove any existing object files and rebuild the library from scratch. This will ensure that all CPU-specific optimizations are enabled during compilation.
  3. Step 3: Recompile pixman with the flag `-march=native` to enable CPU-specific optimizations. For example, you can run the command `gcc -march=native -o libpixman-1.so.0 pixman.c`.

Disabling specific CPU instructions

  1. Step 1: Use a tool like `objdump` to analyze the disassembly of the affected library (libpixman-1.so.0). This will help you identify which specific instruction is causing the error.
  2. Step 2: Look for the instruction that is causing the 'invalid opcode' error and disable it using compiler flags. For example, if the error occurs on the `movq` instruction, you can use the flag `-fno-movbe` to disable this instruction.

✨ Wrapping Up

By recompiling pixman without -march or disabling specific CPU instructions, you should be able to resolve the 'Get Illegal Instruction' error when booting Linux in VirtualBox. It's worth noting that user-mode instructions should not fail to work in a VM, but this may be due to a limitation in the VirtualBox software or other factors. If you continue to experience issues, it may be worth checking the VirtualBox documentation and seeking further assistance from the community.

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