Claude Code 2.1.15 crashes with SIGILL on QEMU VM without AVX support

Description

Claude Code v2.1.15 crashes with an illegal instruction (SIGILL) on a QEMU virtual machine whose virtual CPU lacks AVX support.

Environment

• Claude Code Version: 2.1.15
• OS: Ubuntu (Linux 5.15.0)
• Platform: QEMU VM on Proxmox
• CPU: QEMU Virtual CPU version 2.5+ (no AVX flags exposed)
• CPU Flags: fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc nopl xtopology cpuid tsc_known_freq pni ssse3 cx16 sse4_1 sse4_2 x2apic popcnt aes hypervisor lahf_lm cpuid_fault pti

Note: CPU has SSE4.2 and POPCNT but no AVX/AVX2/AVX-512.

Error Output

bash: line 12: 11878 Illegal instruction     (core dumped) claude --resume ...

============================================================
Bun v1.3.6 (d530ed99) Linux x64 (baseline)
Linux Kernel v5.15.0 | glibc v2.35
CPU: sse42 popcnt
Args: "claude" "--resume" "87705c4d-3724-4fcf-9a8d-d88d13aee988" "--print"
Features: Bun.stderr(2) Bun.stdin(2) Bun.stdout(2) abort_signal fetch(52) jsc no_avx2 no_avx spawn(46) standalone_executable 
Builtins: "bun:main" "node:assert" ...

CPU lacks AVX support. Please consider upgrading to a newer CPU.
panic(main thread): Illegal instruction at address 0x4001FB4
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

Behavior

• v2.1.12: Works correctly (shows version, responds to queries)
• v2.1.14: Crashes with SIGILL
• v2.1.15: Crashes with SIGILL

Expected Behavior

Claude Code should either:

1. Detect AVX capability at startup and gracefully fall back to non-AVX code paths
2. Provide a clear error message before crashing, suggesting to use an older version
3. Offer a non-AVX build for older CPUs and VMs

Workaround

Downgrading to v2.1.12 works. Users can manually symlink to the older version:

ln -sf ~/.local/share/claude/versions/2.1.12 ~/.local/bin/claude

Related Issues

• #13894 - Similar AVX-512 crash on i7-5930K
• #10408 - SIGILL on Intel Mac without AVX2
• #5864 - Request to compile without AVX2 requirement
• #6143 - SIGILL on AMD A6-3420M

Impact

This affects users running Claude Code on:

• Older physical hardware without AVX
• Virtual machines with generic/legacy CPU types (common in Proxmox, VMware, etc.)
• Cloud VMs with older instance types

Many VM environments default to CPU types without AVX for compatibility reasons.