volt-vmm/docs/firecracker-test-results.md

Firecracker Kernel Boot Test Results

Date: 2026-03-07
Firecracker Version: v1.6.0
Test Host: julius (Linux 6.1.0-42-amd64)

Executive Summary

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.

If Volt is using vmlinux-5.10, it will encounter the same ELF loading failure.

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Test Results

Kernel 1: vmlinux-5.10 (FAILS)

Location: projects/volt-vmm/kernels/vmlinux-5.10
Size: 10.5 MB (10,977,280 bytes)
Format: ELF 64-bit LSB executable, x86-64

Firecracker Result:

Start microvm error: Cannot load kernel due to invalid memory configuration 
or invalid kernel image: Kernel Loader: failed to load ELF kernel image

Root Cause Analysis:

readelf: Error: Reading 2304 bytes extends past end of file for section headers

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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Kernel 2: vmlinux.bin (SUCCESS ✓)

Location: comparison/firecracker/vmlinux.bin
Size: 20.4 MB (21,441,304 bytes)
Format: ELF 64-bit LSB executable, x86-64
Version: Linux 4.14.174

Boot Result: SUCCESS
Boot Time: ~93ms to BOOT_COMPLETE

Full Boot Sequence:

[    0.000000] Linux version 4.14.174 (@57edebb99db7) (gcc version 7.5.0)
[    0.000000] Command line: console=ttyS0 reboot=k panic=1 pci=off
[    0.000000] Hypervisor detected: KVM
[    0.000000] kvm-clock: Using msrs 4b564d01 and 4b564d00
[    0.004000] console [ttyS0] enabled
[    0.032000] smpboot: CPU0: Intel(R) Xeon(R) Processor @ 2.40GHz
[    0.074025] virtio-mmio virtio-mmio.0: Failed to enable 64-bit or 32-bit DMA. Trying to continue...
[    0.098589] serial8250: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a U6_16550A
[    0.903994] EXT4-fs (vda): recovery complete
[    0.907903] VFS: Mounted root (ext4 filesystem) on device 254:0.
[    0.916190] Write protecting the kernel read-only data: 12288k
BOOT_COMPLETE 0.93

---

Firecracker Configuration That Works

{
  "boot-source": {
    "kernel_image_path": "./vmlinux.bin",
    "boot_args": "console=ttyS0 reboot=k panic=1 pci=off"
  },
  "drives": [
    {
      "drive_id": "rootfs",
      "path_on_host": "./rootfs.ext4",
      "is_root_device": true,
      "is_read_only": false
    }
  ],
  "machine-config": {
    "vcpu_count": 1,
    "mem_size_mib": 128
  }
}

Key boot arguments:

• console=ttyS0 - Serial console output
• reboot=k - Use keyboard controller for reboot
• panic=1 - Reboot 1 second after panic
• pci=off - Disable PCI (not needed for virtio-mmio)

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ELF Structure Comparison

Property	vmlinux-5.10 (BROKEN)	vmlinux.bin (WORKS)
Entry Point	0x1000000	0x1000000
Program Headers	5	5
Section Headers	36 (claimed)	36
Section Header Offset	43,412,968	21,439,000
File Size	10,977,280	21,441,304
Status	Truncated!	Valid

The vmlinux-5.10 claims section headers at byte 43MB but file is only 10MB.

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Recommendations for Volt

1. Use the Working Kernel for Testing

cp comparison/firecracker/vmlinux.bin kernels/vmlinux-4.14

2. Rebuild vmlinux-5.10 Properly

If 5.10 is needed, rebuild with:

make ARCH=x86_64 vmlinux
# Ensure CONFIG_RELOCATABLE=y for Firecracker
# Ensure CONFIG_PHYSICAL_START=0x1000000

3. Verify Kernel ELF Integrity Before Loading

readelf -h kernel.bin 2>&1 | grep -q "Error" && echo "CORRUPT"

4. Critical Kernel Config for VMM

CONFIG_VIRTIO_MMIO=y
CONFIG_VIRTIO_BLK=y
CONFIG_SERIAL_8250=y
CONFIG_SERIAL_8250_CONSOLE=y
CONFIG_KVM_GUEST=y
CONFIG_PARAVIRT=y

---

Boot Timeline Analysis (vmlinux.bin)

Time (ms)	Event
0	Kernel start, memory setup
4	Console enabled, TSC calibration
32	SMP init, CPU brought up
74	virtio-mmio device registered
99	Serial driver loaded (ttyS0)
385	i8042 keyboard init
897	Root filesystem mounted
920	Kernel read-only protection
930	BOOT_COMPLETE

Total boot time: ~93ms to userspace

---

Commands Used

# Start Firecracker with API socket
./firecracker --api-sock /tmp/fc.sock &

# Configure boot source
curl -s --unix-socket /tmp/fc.sock -X PUT "http://localhost/boot-source" \
  -H "Content-Type: application/json" \
  -d '{"kernel_image_path": "./vmlinux.bin", "boot_args": "console=ttyS0 reboot=k panic=1 pci=off"}'

# Configure rootfs
curl -s --unix-socket /tmp/fc.sock -X PUT "http://localhost/drives/rootfs" \
  -H "Content-Type: application/json" \
  -d '{"drive_id": "rootfs", "path_on_host": "./rootfs.ext4", "is_root_device": true, "is_read_only": false}'

# Configure machine
curl -s --unix-socket /tmp/fc.sock -X PUT "http://localhost/machine-config" \
  -H "Content-Type: application/json" \
  -d '{"vcpu_count": 1, "mem_size_mib": 128}'

# Start VM
curl -s --unix-socket /tmp/fc.sock -X PUT "http://localhost/actions" \
  -H "Content-Type: application/json" \
  -d '{"action_type": "InstanceStart"}'

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Conclusion

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.

Action Required: Use vmlinux.bin for Volt testing, or rebuild vmlinux-5.10 from source with complete ELF sections.