wekan/snap-src/bin/cpu-exec

#!/bin/bash
# ─────────────────────────────────────────────────────────────────────────────
# cpu-exec: run a binary directly when the CPU has every instruction-set
# feature the binary needs, otherwise transparently re-run it through
# qemu-user emulation (which implements the full modern instruction set).
# General mechanism for ALL scripts, sandboxes, platforms and CPUs (#6458).
#
# Why: MongoDB >= 5.0 x86_64 binaries require AVX — on CPUs without it (old
# Intel/AMD, and hypervisors/sandboxes that mask AVX: some QEMU/KVM/Proxmox
# configurations, which is exactly the reported #6458 environment) mongod dies
# instantly with SIGILL (exit 132). MongoDB >= 5 arm64 similarly requires
# ARMv8.2-A (Raspberry Pi 4 and older are ARMv8.0). The snap's old
# migratemongo/avx wrappers did this per-tool, amd64-only, and only for PATH
# lookups — every script invoking $SNAP/bin/mongod by ABSOLUTE path bypassed
# them. This helper replaces that with one general, explicit mechanism.
#
# Usage:
#   cpu-exec [--features <arch>=<f1>[+<f2>...][,<arch>=...]] <binary> [args...]
#
#   --features declares the CPU features the binary needs, per architecture:
#       cpu-exec --features x86_64=avx,aarch64=atomics mongod --dbpath ...
#   Only the entry matching `uname -m` is checked (against /proc/cpuinfo
#   flags/Features). No --features, an empty spec, or no entry for the current
#   architecture means "no special requirements" — the binary is exec'd
#   directly with zero overhead, so it is safe to route EVERY binary through
#   cpu-exec. The WEKAN_REQUIRED_CPU_FEATURES environment variable, when set,
#   overrides --features (same syntax).
#
#   Note: `aarch64=atomics` (LSE, ARMv8.1) is the practical /proc/cpuinfo
#   proxy for MongoDB's ARMv8.2-A requirement — Cortex-A53/A72 (Raspberry Pi
#   3/4) lack it, ARMv8.2-A cores have it.
#
# qemu-user lookup order (first executable wins):
#   1. $WEKAN_QEMU_USER (explicit override)
#   2. qemu-<arch> next to this script       (bundle .zip / Docker /build)
#   3. $SNAP/qemu-<arch>, $SNAP/bin/qemu-<arch>
#   4. $SNAP/migratemongo/avx/qemu-x86_64    (existing snap amd64 bundle)
#   5. qemu-<arch> / qemu-<arch>-static on PATH
# If none is found, a clear error is printed and the binary runs directly so
# the real failure (SIGILL) surfaces in the logs instead of hiding.
#
# WEKAN_CPUINFO overrides the /proc/cpuinfo path (used by the unit tests).
# ─────────────────────────────────────────────────────────────────────────────
set -u

FEATURES_SPEC=""
if [ "${1:-}" = "--features" ]; then
    FEATURES_SPEC="${2:-}"
    shift 2
fi
[ -n "${WEKAN_REQUIRED_CPU_FEATURES:-}" ] && FEATURES_SPEC="${WEKAN_REQUIRED_CPU_FEATURES}"

if [ $# -lt 1 ]; then
    echo "Usage: cpu-exec [--features arch=feat1+feat2,arch2=...] <binary> [args...]" >&2
    exit 64
fi

ARCH="$(uname -m)"
CPUINFO="${WEKAN_CPUINFO:-/proc/cpuinfo}"

# Pick this architecture's '+'-separated feature list out of the spec.
required=""
IFS=',' read -r -a _entries <<< "$FEATURES_SPEC"
for _e in "${_entries[@]:-}"; do
    case "$_e" in
        "$ARCH"=*) required="${_e#*=}" ;;
    esac
done

# Which of the required features is the CPU missing? x86 lists them on
# "flags :" lines, ARM on "Features :" lines.
missing=""
if [ -n "$required" ] && [ -r "$CPUINFO" ]; then
    IFS='+' read -r -a _feats <<< "$required"
    for _f in "${_feats[@]:-}"; do
        [ -z "$_f" ] && continue
        grep -Eiq "^(flags|features)[[:space:]]*:.*[[:space:]]${_f}([[:space:]]|$)" "$CPUINFO" \
            || missing="${missing} ${_f}"
    done
fi

if [ -z "$missing" ]; then
    exec "$@"
fi

# The CPU lacks something this binary needs: find a same-architecture
# qemu-user to emulate the missing instructions.
HERE="$(cd "$(dirname "$0")" 2>/dev/null && pwd)"
QEMU=""
for candidate in \
    "${WEKAN_QEMU_USER:-}" \
    "${HERE:+$HERE/qemu-$ARCH}" \
    "${SNAP:+$SNAP/qemu-$ARCH}" \
    "${SNAP:+$SNAP/bin/qemu-$ARCH}" \
    "${SNAP:+$SNAP/migratemongo/avx/qemu-$ARCH}" \
    "$(command -v "qemu-$ARCH" 2>/dev/null)" \
    "$(command -v "qemu-$ARCH-static" 2>/dev/null)"; do
    if [ -n "$candidate" ] && [ -x "$candidate" ]; then
        QEMU="$candidate"
        break
    fi
done

if [ -n "$QEMU" ]; then
    echo "cpu-exec: this CPU lacks${missing}; running $1 through qemu-user emulation ($QEMU)." >&2
    echo "cpu-exec: emulation is slower — consider migrating to FerretDB (no special CPU features needed)." >&2
    exec "$QEMU" "$@"
fi

echo "cpu-exec: ERROR: this CPU lacks${missing} and no qemu-user (qemu-$ARCH) was found;" >&2
echo "cpu-exec: running $1 directly — expect SIGILL (Illegal instruction). Install qemu-user(-static) or migrate to FerretDB." >&2
exec "$@"