Volt VMM (Neutron Stardust): source-available under AGPSL v5.0
KVM-based microVMM for the Volt platform: - Sub-second VM boot times - Minimal memory footprint - Landlock LSM + seccomp security - Virtio device support - Custom kernel management Copyright (c) Armored Gates LLC. All rights reserved. Licensed under AGPSL v5.0
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Karl Clinger
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docs/firecracker-test-results.md
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docs/firecracker-test-results.md
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# Firecracker Kernel Boot Test Results
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**Date:** 2026-03-07
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**Firecracker Version:** v1.6.0
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**Test Host:** julius (Linux 6.1.0-42-amd64)
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## Executive Summary
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**CRITICAL FINDING:** The `vmlinux-5.10` kernel in `kernels/` directory **FAILS TO LOAD** in Firecracker due to corrupted/truncated section headers. The working kernel `vmlinux.bin` (4.14.174) boots successfully in ~93ms.
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If Volt is using `vmlinux-5.10`, it will encounter the same ELF loading failure.
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---
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## Test Results
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### Kernel 1: vmlinux-5.10 (FAILS)
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**Location:** `projects/volt-vmm/kernels/vmlinux-5.10`
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**Size:** 10.5 MB (10,977,280 bytes)
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**Format:** ELF 64-bit LSB executable, x86-64
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**Firecracker Result:**
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```
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Start microvm error: Cannot load kernel due to invalid memory configuration
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or invalid kernel image: Kernel Loader: failed to load ELF kernel image
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```
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**Root Cause Analysis:**
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```
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readelf: Error: Reading 2304 bytes extends past end of file for section headers
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```
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The ELF file has **missing/corrupted section headers** at offset 43,412,968 (claimed) but file is only 10,977,280 bytes. This is a truncated or improperly built kernel.
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---
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### Kernel 2: vmlinux.bin (SUCCESS ✓)
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**Location:** `comparison/firecracker/vmlinux.bin`
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**Size:** 20.4 MB (21,441,304 bytes)
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**Format:** ELF 64-bit LSB executable, x86-64
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**Version:** Linux 4.14.174
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**Boot Result:** SUCCESS
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**Boot Time:** ~93ms to `BOOT_COMPLETE`
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**Full Boot Sequence:**
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```
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[ 0.000000] Linux version 4.14.174 (@57edebb99db7) (gcc version 7.5.0)
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[ 0.000000] Command line: console=ttyS0 reboot=k panic=1 pci=off
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[ 0.000000] Hypervisor detected: KVM
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[ 0.000000] kvm-clock: Using msrs 4b564d01 and 4b564d00
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[ 0.004000] console [ttyS0] enabled
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[ 0.032000] smpboot: CPU0: Intel(R) Xeon(R) Processor @ 2.40GHz
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[ 0.074025] virtio-mmio virtio-mmio.0: Failed to enable 64-bit or 32-bit DMA. Trying to continue...
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[ 0.098589] serial8250: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a U6_16550A
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[ 0.903994] EXT4-fs (vda): recovery complete
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[ 0.907903] VFS: Mounted root (ext4 filesystem) on device 254:0.
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[ 0.916190] Write protecting the kernel read-only data: 12288k
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BOOT_COMPLETE 0.93
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```
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---
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## Firecracker Configuration That Works
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```json
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{
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"boot-source": {
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"kernel_image_path": "./vmlinux.bin",
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"boot_args": "console=ttyS0 reboot=k panic=1 pci=off"
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},
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"drives": [
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{
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"drive_id": "rootfs",
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"path_on_host": "./rootfs.ext4",
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"is_root_device": true,
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"is_read_only": false
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}
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],
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"machine-config": {
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"vcpu_count": 1,
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"mem_size_mib": 128
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}
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}
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```
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**Key boot arguments:**
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- `console=ttyS0` - Serial console output
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- `reboot=k` - Use keyboard controller for reboot
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- `panic=1` - Reboot 1 second after panic
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- `pci=off` - Disable PCI (not needed for virtio-mmio)
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---
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## ELF Structure Comparison
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| Property | vmlinux-5.10 (BROKEN) | vmlinux.bin (WORKS) |
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|----------|----------------------|---------------------|
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| Entry Point | 0x1000000 | 0x1000000 |
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| Program Headers | 5 | 5 |
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| Section Headers | 36 (claimed) | 36 |
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| Section Header Offset | 43,412,968 | 21,439,000 |
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| File Size | 10,977,280 | 21,441,304 |
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| **Status** | Truncated! | Valid |
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The vmlinux-5.10 claims section headers at byte 43MB but file is only 10MB.
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---
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## Recommendations for Volt
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### 1. Use the Working Kernel for Testing
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```bash
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cp comparison/firecracker/vmlinux.bin kernels/vmlinux-4.14
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```
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### 2. Rebuild vmlinux-5.10 Properly
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If 5.10 is needed, rebuild with:
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```bash
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make ARCH=x86_64 vmlinux
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# Ensure CONFIG_RELOCATABLE=y for Firecracker
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# Ensure CONFIG_PHYSICAL_START=0x1000000
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```
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### 3. Verify Kernel ELF Integrity Before Loading
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```bash
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readelf -h kernel.bin 2>&1 | grep -q "Error" && echo "CORRUPT"
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```
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### 4. Critical Kernel Config for VMM
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```
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CONFIG_VIRTIO_MMIO=y
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CONFIG_VIRTIO_BLK=y
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CONFIG_SERIAL_8250=y
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CONFIG_SERIAL_8250_CONSOLE=y
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CONFIG_KVM_GUEST=y
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CONFIG_PARAVIRT=y
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```
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---
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## Boot Timeline Analysis (vmlinux.bin)
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| Time (ms) | Event |
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|-----------|-------|
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| 0 | Kernel start, memory setup |
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| 4 | Console enabled, TSC calibration |
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| 32 | SMP init, CPU brought up |
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| 74 | virtio-mmio device registered |
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| 99 | Serial driver loaded (ttyS0) |
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| 385 | i8042 keyboard init |
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| 897 | Root filesystem mounted |
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| 920 | Kernel read-only protection |
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| 930 | BOOT_COMPLETE |
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**Total boot time: ~93ms to userspace**
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---
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## Commands Used
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```bash
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# Start Firecracker with API socket
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./firecracker --api-sock /tmp/fc.sock &
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# Configure boot source
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curl -s --unix-socket /tmp/fc.sock -X PUT "http://localhost/boot-source" \
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-H "Content-Type: application/json" \
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-d '{"kernel_image_path": "./vmlinux.bin", "boot_args": "console=ttyS0 reboot=k panic=1 pci=off"}'
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# Configure rootfs
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curl -s --unix-socket /tmp/fc.sock -X PUT "http://localhost/drives/rootfs" \
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-H "Content-Type: application/json" \
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-d '{"drive_id": "rootfs", "path_on_host": "./rootfs.ext4", "is_root_device": true, "is_read_only": false}'
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# Configure machine
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curl -s --unix-socket /tmp/fc.sock -X PUT "http://localhost/machine-config" \
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-H "Content-Type: application/json" \
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-d '{"vcpu_count": 1, "mem_size_mib": 128}'
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# Start VM
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curl -s --unix-socket /tmp/fc.sock -X PUT "http://localhost/actions" \
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-H "Content-Type: application/json" \
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-d '{"action_type": "InstanceStart"}'
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```
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---
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## Conclusion
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The kernel issue is **not with Firecracker or Volt's VMM** - it's a corrupted kernel image. The `vmlinux.bin` kernel (4.14.174) proves that Firecracker can successfully boot VMs on this host with proper kernel images.
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**Action Required:** Use `vmlinux.bin` for Volt testing, or rebuild `vmlinux-5.10` from source with complete ELF sections.
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