fix(rootfs/qemu-static): use direct armhf exec probe instead of broken arch-test gate

extensions/arm64-compat-vdso.sh

@@ -1,4 +1,15 @@
 # Enable 32-bit compat vDSO for arm64 kernels with GCC or clang.
+#
+# Builds the kernel with CONFIG_COMPAT + COMPAT_VDSO + ARM64_32BIT_EL0, letting
+# an arm64 host running this kernel execute armhf (32-bit ARM) userspace
+# natively at full speed. One concrete use case is Armbian's rootfs phase: on
+# such a host, armhf chroot / package post-install steps run native instead of
+# through qemu-user-static (~10× faster). See lib/functions/rootfs/qemu-static.sh
+# and the ARMBIAN_PREFER_NATIVE_ARMHF build switch.
+#
+# Note: aarch64 silicon without 32-bit ARM userspace support at EL0 (notably
+# Apple M-series) cannot run armhf even with this kernel option enabled.
+#
 # Requirements:
 # - arm64 build target (ARCH=arm64, ARCHITECTURE=arm64).
 # - For GCC builds: a 32-bit ARM cross-compiler (default prefix arm-linux-gnueabi-),
@@ -25,7 +36,7 @@ function host_dependencies_ready__arm64_compat_vdso() {
 	fi
 
 	local compat_gcc_prefix="${CROSS_COMPILE_COMPAT:-"arm-linux-gnueabi-"}"
-	if ! command -v "${compat_gcc_prefix}gcc" >/dev/null 2>&1; then
+	if ! command -v "${compat_gcc_prefix}gcc" > /dev/null 2>&1; then
 		exit_with_error "Missing 32-bit compiler '${compat_gcc_prefix}gcc' for COMPAT_VDSO; install gcc-arm-linux-gnueabi or set CROSS_COMPILE_COMPAT"
 	fi
 }
@@ -46,7 +57,7 @@ function custom_kernel_config__arm64_compat_vdso() {
 	opts_y+=("COMPAT" "COMPAT_VDSO" "ARM64_32BIT_EL0")
 
 	if [[ -f .config ]]; then
-		kconfig_hit="$(grep -R -n -m1 "COMPAT_VDSO" arch/arm64 Kconfig* 2>/dev/null || true)"
+		kconfig_hit="$(grep -R -n -m1 "COMPAT_VDSO" arch/arm64 Kconfig* 2> /dev/null || true)"
 		if [[ -z "${kconfig_hit}" ]]; then
 			exit_with_error "Selected kernel tree lacks COMPAT_VDSO support for arm64"
 		fi

lib/functions/rootfs/qemu-static.sh

@@ -193,35 +193,131 @@ function prepare_host_binfmt_qemu_cross() {
 }
 
 function prepare_host_binfmt_qemu_cross_arm64_host_armhf_target() {
-	display_alert "Trying to update binfmts - aarch64 mostly does 32-bit sans emulation, but Apple said no" "update-binfmts --enable qemu-${wanted_arch}" "debug"
-	run_host_command_logged update-binfmts --enable "qemu-${wanted_arch}" "&>" "/dev/null" "||" "true" # don't fail nor produce output, which can be misleading.
+	declare armhf_probe="/usr/arm-linux-gnueabihf/lib/ld-linux-armhf.so.3"
+	declare prefer_native="${ARMBIAN_PREFER_NATIVE_ARMHF:-yes}"
+	declare qemu_arm_was_enabled=0
+
+	# Snapshot qemu-arm state — drives both COMPAT probe and trust-existing.
+	if [[ -e /proc/sys/fs/binfmt_misc/qemu-arm ]] &&
+		[[ "$(head -n1 /proc/sys/fs/binfmt_misc/qemu-arm 2> /dev/null)" == "enabled" ]]; then
+		qemu_arm_was_enabled=1
+	fi
+
+	# COMPAT probe must run with qemu-arm OFF, otherwise kernel routes
+	# armhf exec through qemu and the probe lies. Temp-disable, probe,
+	# restore on failure. `arch-test arm` is unreliable (probes ARMv5,
+	# COMPAT needs ≥v7); ld-linux-armhf comes from gcc-arm-linux-gnueabihf
+	# (armbian host dep for armhf|all). Toggle needs CAP_SYS_ADMIN — present
+	# in Armbian's docker_cli_prepare_launch; if /proc is read-only anyway,
+	# skip the probe gracefully and trust existing qemu-arm.
+	if [[ "${prefer_native}" == "yes" ]] && [[ -x "${armhf_probe}" ]]; then
+		declare toggle_ok=1
+		if ((qemu_arm_was_enabled)); then
+			echo 0 > /proc/sys/fs/binfmt_misc/qemu-arm 2> /dev/null || toggle_ok=0
+		fi
+		if ((toggle_ok)) && "${armhf_probe}" --help > /dev/null 2>&1; then
+			display_alert "Host kernel can run armhf natively (CONFIG_COMPAT)" "qemu-arm left disabled if it was on" "info"
+			return 0
+		fi
+		if ((qemu_arm_was_enabled && toggle_ok)); then
+			echo 1 > /proc/sys/fs/binfmt_misc/qemu-arm ||
+				exit_with_error "Failed to restore qemu-arm after failed native armhf probe"
+		fi
+	fi
+
+	# Native COMPAT unavailable (or opt-out via ARMBIAN_PREFER_NATIVE_ARMHF=no).
+	# Trust existing qemu-arm registration only if it actually executes —
+	# `enabled` flag alone doesn't tell us the interpreter is runnable
+	# (stale path, removed package). Validate via arch-test.
+	if ((qemu_arm_was_enabled)); then
+		if command -v arch-test > /dev/null 2>&1 && arch-test arm > /dev/null 2>&1; then
+			display_alert "qemu-arm enabled and functional" "trusting existing setup" "debug"
+			return 0
+		fi
+		display_alert "qemu-arm enabled but execution probe failed" "stale registration — reconfiguring" "warn"
+	fi
+
+	# ld-linux-armhf may be absent on cross builds whose target isn't
+	# armhf (gcc-arm-linux-gnueabihf isn't pulled in then). Fall back to
+	# arch-test to avoid degraded host-capability detection on those
+	# flows; on Ampere CAX it reports false-negative but the probe above
+	# already covered the armhf-target case where it matters most.
+	if [[ ! -x "${armhf_probe}" ]] && command -v arch-test > /dev/null 2>&1 && arch-test arm > /dev/null 2>&1; then
+		display_alert "Host can run armhf (arch-test fallback)" "no qemu-arm setup needed" "debug"
+		return 0
+	fi
+
+	# No native COMPAT — need qemu-arm. Prefer a packaged descriptor
+	# (qemu-user-binfmt on resolute installs `/usr/bin/qemu-arm`;
+	# qemu-user-static elsewhere uses the -static suffix). Overwriting
+	# it would break the resolute interpreter path.
+	if [[ -f /usr/share/binfmts/qemu-arm ]]; then
+		# Three-step recovery: re-import the descriptor into binfmt-support's
+		# admin DB (handles stale/empty DB where --enable would fail with
+		# "not in database"); --enable activates the format; force-sync via
+		# /proc afterwards if the kernel entry was externally toggled to 0.
+		run_host_command_logged update-binfmts --import qemu-arm 2> /dev/null || true
+		run_host_command_logged update-binfmts --enable qemu-arm || true
+		[[ -e /proc/sys/fs/binfmt_misc/qemu-arm ]] && echo 1 > /proc/sys/fs/binfmt_misc/qemu-arm 2> /dev/null || true
+		if [[ -e /proc/sys/fs/binfmt_misc/qemu-arm ]] &&
+			[[ "$(head -n1 /proc/sys/fs/binfmt_misc/qemu-arm 2> /dev/null)" == "enabled" ]]; then
+			_verify_qemu_arm_executes
+			display_alert "qemu-arm enabled via packaged descriptor" "leaving package-provided setup intact" "debug"
+			return 0
+		fi
+		exit_with_error "/usr/share/binfmts/qemu-arm exists but qemu-arm could not be enabled — packaged interpreter likely missing. Reinstall qemu-user-binfmt (resolute) / qemu-user-static, or remove the descriptor and retry."
+	fi
+
+	# Kernel entry exists but disabled, no descriptor on host. The kernel
+	# keeps the magic/mask in memory once registered; only the enabled
+	# flag toggles. Try `echo 1 > /proc/...` before giving up — that
+	# repairs the common "someone toggled it off" state without needing
+	# the descriptor file back.
+	if [[ -e /proc/sys/fs/binfmt_misc/qemu-arm ]]; then
+		echo 1 > /proc/sys/fs/binfmt_misc/qemu-arm 2> /dev/null || true
+		if [[ "$(head -n1 /proc/sys/fs/binfmt_misc/qemu-arm 2> /dev/null)" == "enabled" ]]; then
+			_verify_qemu_arm_executes
+			display_alert "qemu-arm re-enabled via /proc" "kernel state restored without descriptor" "debug"
+			return 0
+		fi
+		exit_with_error "qemu-arm kernel entry present but cannot be re-enabled and no descriptor to re-register from. Reinstall qemu-user-binfmt / qemu-user-static and retry."
+	fi
+
+	# Apple-Silicon-like (no COMPAT, no qemu pkg): hand-roll the descriptor.
+	display_alert "arm64 host can't run armhf natively (no CONFIG_COMPAT?)" "importing+enabling qemu-arm" "debug"
+	cat <<- BINFMT_ARM_MAGIC > /usr/share/binfmts/qemu-arm
+		package qemu-user-static
+		interpreter /usr/bin/qemu-arm-static
+		magic \x7f\x45\x4c\x46\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00
+		offset 0
+		mask \xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff
+		credentials yes
+		fix_binary no
+		preserve yes
+	BINFMT_ARM_MAGIC
+	run_host_command_logged update-binfmts --import qemu-arm
+	run_host_command_logged update-binfmts --enable qemu-arm
 
 	if [[ "${SHOW_DEBUG}" == "yes" ]]; then
 		display_alert "Debugging arch-test" "full output" "debug"
-		run_host_command_logged arch-test "||" true
+		run_host_command_logged arch-test || true
 	fi
+	_verify_qemu_arm_executes
+	display_alert "arm 32-bit emulation on arm64" "has been set up via qemu-arm" "cachehit"
+}
 
-	# to check, we use arch-test; if will return 0 if _either_ the host can natively run armhf, or if qemu-arm is correctly working.
-	if arch-test arm; then
-		display_alert "Host can run armhf natively or emulation is correctly setup already" "no need to enable qemu-arm" "debug"
-	else
-		display_alert "arm64 host can't run armhf natively" "importing enabling qemu-arm" "debug"
-		cat <<-BINFMT_ARM_MAGIC >/usr/share/binfmts/qemu-arm
-			package qemu-user-static
-			interpreter /usr/bin/qemu-arm-static
-			magic \x7f\x45\x4c\x46\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00
-			offset 0
-			mask \xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff
-			credentials yes
-			fix_binary no
-			preserve yes
-		BINFMT_ARM_MAGIC
-		run_host_command_logged update-binfmts --import "qemu-${wanted_arch}"
-		run_host_command_logged update-binfmts --enable "qemu-${wanted_arch}"
-
-		# Test again using arch-test.
-		display_alert "Checking if arm 32-bit emulation on arm64 works after enabling" "qemu-arm emulation" "info"
-		run_host_command_logged arch-test arm
-		display_alert "arm 32-bit emulation on arm64" "has been correctly setup" "cachehit"
+# Helper: confirm qemu-arm interpreter actually runs an armhf binary.
+# `update-binfmts --enable` and an `enabled` flag in /proc only attest
+# registration state, not runtime executability — a stale interpreter
+# path or removed package slips through and fails later in chroot. Run
+# `arch-test arm` here so we fail fast at host-prepare time.
+function _verify_qemu_arm_executes() {
+	if ! command -v arch-test > /dev/null 2>&1; then
+		display_alert "qemu-arm runtime verification skipped" "arch-test not available on host" "warn"
+		return 0
+	fi
+	if arch-test arm > /dev/null 2>&1; then
+		return 0
 	fi
+	exit_with_error "qemu-arm registered but armhf execution fails. Interpreter likely broken (stale path, removed package, missing qemu-arm-static). Reinstall qemu-user-binfmt (resolute) / qemu-user-static and retry."
 }