DE25: aarch64 stage-1 initramfs + qemu-system-aarch64 test leg (stage 1 becomes a fragment stack)

.github/actions/buildroot-build/action.yml

@@ -269,7 +269,13 @@ runs:
         # this is shell, and both halves read the same env var either way.
         # See docs/ci.md#cache-keys.
         tc_hash=$(sha256sum .br-toolchain-fingerprint | cut -d' ' -f1)
-        ir_hash=$(sha256sum configs/mister_initramfs_defconfig | cut -d' ' -f1)
+        # The stage-1 configuration is the initramfs-de10nano fragment stack
+        # (configs/fragments/stacks.mk), read through the same helper as the
+        # image/kernel stacks above so a fragment added to the stack moves this
+        # key without anyone editing a list here.
+        mapfile -t ir_files < <(config_stack_files INITRAMFS_DE10NANO)
+        [ "${#ir_files[@]}" -gt 0 ] || { echo "::error::configs/fragments/stacks.mk names no fragments for INITRAMFS_DE10NANO" >&2; exit 1; }
+        ir_hash=$(cat "${ir_files[@]}" | sha256sum | cut -d' ' -f1)
         echo "BR_INITRAMFS_HOST_KEY=br-initramfs-host-${ws_fp}-${ver}-${ir_hash}" >> "$GITHUB_ENV"
 
         # Variant-resolved host-toolchain key + paths (main's key STRING

README.md

@@ -609,9 +609,11 @@ configs/fragments/       stacks.mk                  (which fragments form which
                          de10nano-image.fragment    (the shipped image: hooks, ext4, packages)
                          kernel-only.fragment       (kernel-only base, shared by variants)
                          de25nano.fragment          (DE25-Nano developer OS, aarch64)
+                         initramfs-common.fragment  (stage-1 cpio: everything but the arch)
+                         initramfs-de10nano.fragment / initramfs-de25nano.fragment
+                                                    (stage-1 arch/ABI + headers, per board)
                          golden.sha256              (resolved-config hashes CI asserts)
 configs/                 mister_rt.fragment         (PREEMPT_RT / 7.x delta)
-                         mister_initramfs_defconfig (stage-1 cpio)
                          mister_installer_defconfig (SD-card installer cpio)
                          -> docs/buildroot-config.md has the rationale for every line
 board/mister/de10nano/
@@ -763,6 +765,7 @@ Two things that will bite you otherwise:
 | `make rt` | Kernel-only `PREEMPT_RT` build → `zImage_dtb-rt` + module overlay |
 | `make sdcard` | Full `sdcard.img(.xz)` — run **after** `make all`. The card carries no variant kernel, so `make rt` is not required first; if you *do* build RT, run it before `make all` so its modules land in the image |
 | `make initramfs` | Stage-1 cpio only, and print its size |
+| `make de25-initramfs` | The same stage 1 built for aarch64 (`output-initramfs-de25/`), verified; boot-test it with `scripts/test-initramfs.sh --board de25nano` |
 | `make menuconfig` / `linux-menuconfig` | Interactive Buildroot / kernel config |
 | `make savedefconfig` | Write the config back to the defconfig (**always** do this after editing) |
 | `make buildroot-verify` | Download + SHA-256-verify the pinned Buildroot tarball |
@@ -802,7 +805,8 @@ broke and why, without grepping):
 - the image-contract checks — `check-zimage-dtb.sh`, `check-linux-img.sh`,
   `check-size-budget.sh`
 - the structural initramfs checks, plus a **full QEMU boot test of the initramfs `/init`**
-  (booted six times, across the failure paths)
+  (eight cases, across the failure paths — and the same eight again on
+  `qemu-system-aarch64` for the aarch64 build of the same `/init`, when it has been built)
 - an ABI smoke test running the **stock `MiSTer` binary** under `qemu-user` against the
   built rootfs: dynamic linking must resolve clean, and it must die at FPGA access and not
   one instruction earlier

board/mister/de10nano/initramfs-post-build.sh → board/mister/common/initramfs-post-build.sh

@@ -4,7 +4,7 @@
 #
 # Stage-1 (initramfs) post-build hook. Runs after the cpio's target tree is
 # assembled and before the cpio is generated (BR2_ROOTFS_POST_BUILD_SCRIPT in
-# configs/mister_initramfs_defconfig). Reproducible: no timestamps, no
+# configs/fragments/initramfs-common.fragment). Reproducible: no timestamps, no
 # randomness, no network -- it only deletes files (A9).
 #
 # WHY THIS EXISTS -- exfatprogs ships six binaries and /init calls one.
@@ -55,7 +55,7 @@ done
 # it exists to catch. Keep the two in step if either ever moves.
 [ -x "${TARGET_DIR}/usr/sbin/fsck.exfat" ] || {
 	echo "FATAL: initramfs-post-build.sh: no ${TARGET_DIR}/usr/sbin/fsck.exfat." >&2
-	echo "       BR2_PACKAGE_EXFATPROGS is set in configs/mister_initramfs_defconfig," >&2
+	echo "       BR2_PACKAGE_EXFATPROGS is set in configs/fragments/initramfs-common.fragment," >&2
 	echo "       so the package moved its install path. The initramfs /init hardcodes" >&2
 	echo "       FSCK_EXFAT=/usr/sbin/fsck.exfat; update both together. See ADR 0026." >&2
 	exit 1

board/mister/de10nano/installer-busybox.config

@@ -138,7 +138,7 @@
 # ############################################################################
 #
 #
-# Hand-derived from board/mister/de10nano/initramfs-busybox.config
+# Hand-derived from board/mister/common/initramfs-busybox.config
 # (see header above for the diff and rationale); NOT regenerated verbatim by
 # `make busybox-update-config` — do that, then re-apply this file's five
 # additions, after any BusyBox version bump.

board/mister/de10nano/installer-overlay/init

@@ -73,7 +73,7 @@
 #   copy the base and SKIP the cores with a loud message rather than OOM-bricking.
 #   update_all.sh on the installed card fetches cores anyway.
 # * DEFENSIVE LIKE THE STAGE-1 init. Same contract as
-#   board/mister/de10nano/initramfs-overlay/init: early proc/sys/dev mounts, parse
+#   board/mister/common/initramfs-overlay/init: early proc/sys/dev mounts, parse
 #   the cmdline (never hardcode the device), and on ANY fatal error print a banner
 #   and drop to a RESPAWNING rescue shell. PID 1 must NEVER exit (that is an instant
 #   kernel panic). A half-reformatted card must give a diagnosable message, not a