Support GitHub Actions aarch64 runners

GitHub now offers free aarch64 runners: https://github.blog/changelog/2025-01-16-linux-arm64-hosted-runners-now-available-for-free-in-public-repositories-public-preview/ Automatically select the default apk-tools-url and arch to match the CPU architecture of the current runner. Run armv7 and armhf without QEMU on aarch64 runners. For symmetry, allow emulating x86 and x86_64 on aarch64. Document how to run aarch64 without emulation. Change existing aarch64 examples to s390x, to avoid encouraging emulation of aarch64. Fixes jirutka#11.
bgilbert · Jan 17, 2025 · 2237981 · 2237981
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diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -10,11 +10,13 @@ jobs:
           - edge
         arch:
           - x86_64
-          - aarch64  # emulated
+          - aarch64
         host-os:
           - ubuntu-latest
           - ubuntu-24.04
           - ubuntu-22.04
+          - ubuntu-24.04-arm
+          - ubuntu-22.04-arm
     runs-on: ${{ matrix.host-os }}
     env:
       MY_JOB_VAR: 'allons-y!'
@@ -86,7 +88,12 @@ jobs:
         run: test -f "${{ steps.setup-alpine.outputs.root-path }}"/etc/alpine-release
 
   test-multi:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.host-os }}
+    strategy:
+      matrix:
+        host-os:
+          - ubuntu-latest
+          - ubuntu-24.04-arm
     steps:
       - uses: actions/checkout@v4
 

diff --git a/README.adoc b/README.adoc
@@ -53,13 +53,13 @@ URL of the apk-tools static binary to use.
 It must end with `#!sha256!` followed by a SHA-256 hash of the file.
 This should normally be left at the default value.
 +
-Default: _see link:action.yml[]_
+Default: _see link:setup-alpine.sh[]_
 
 [[arch]] arch::
 CPU architecture to emulate using https://www.qemu.org/docs/master/user/main.html[QEMU user space emulator].
-Allowed values are: `x86_64` (native), `x86` (native), `aarch64`, `armhf` footnote:[armhf is armv6 with hard-float.], `armv7`, `loongarch64` footnote:[loongarch64 is available since v3.21.], `ppc64le`, `riscv64` footnote:[riscv64 is available since v3.20.], and `s390x`.
+Allowed values are: `x86_64` (native on x86_64), `x86` (native on x86_64), `aarch64` (native on aarch64), `armhf` footnote:[armhf is armv6 with hard-float.] (native on aarch64), `armv7` (native on aarch64), `loongarch64` footnote:[loongarch64 is available since v3.21.], `ppc64le`, `riscv64` footnote:[riscv64 is available since v3.20.], and `s390x`.
 +
-Default: `x86_64`
+Default: _runner's native architecture_
 
 branch::
 Alpine branch (aka release) to install: `vMAJOR.MINOR`, `latest-stable`, or `edge`.
@@ -159,19 +159,34 @@ steps:
 ----
 
 
+=== Set up and use Alpine natively on aarch64
+
+[source, yaml, subs="+attributes"]
+----
+runs-on: ubuntu-24.04-arm
+steps:
+  - name: Setup latest Alpine Linux
+    uses: {action-ref}
+
+  - name: Run script inside Alpine chroot
+    run: uname -m
+    shell: alpine.sh {0}
+----
+
+
 === Set up and use Alpine for a different CPU architecture
 
 [source, yaml, subs="+attributes"]
 ----
 runs-on: ubuntu-latest
 steps:
-  - name: Setup Alpine Linux {alpine-latest} for aarch64
+  - name: Setup Alpine Linux {alpine-latest} for s390x
     uses: {action-ref}
     with:
-      arch: aarch64
+      arch: s390x
       branch: {alpine-latest}
 
-  - name: Run script inside Alpine chroot with aarch64 emulation
+  - name: Run script inside Alpine chroot with s390x emulation
     run: uname -m
     shell: alpine.sh {0}
 ----
@@ -200,19 +215,19 @@ steps:
     with:
       shell-name: alpine-x86_64.sh
 
-  - name: Setup latest Alpine Linux for aarch64
+  - name: Setup latest Alpine Linux for s390x
     uses: {action-ref}
     with:
-      arch: aarch64
-      shell-name: alpine-aarch64.sh
+      arch: s390x
+      shell-name: alpine-s390x.sh
 
   - name: Run script inside Alpine chroot
     run: uname -m
     shell: alpine-x86_64.sh {0}
 
-  - name: Run script inside Alpine chroot with aarch64 emulation
+  - name: Run script inside Alpine chroot with s390x emulation
     run: uname -m
-    shell: alpine-aarch64.sh {0}
+    shell: alpine-s390x.sh {0}
 
   - name: Run script on the host system (Ubuntu)
     run: cat /etc/os-release
@@ -229,8 +244,8 @@ runs-on: ubuntu-latest
 strategy:
   matrix:
     include:
-      - rust-target: aarch64-unknown-linux-musl
-        os-arch: aarch64
+      - rust-target: s390x-unknown-linux-musl
+        os-arch: s390x
 env:
   CROSS_SYSROOT: /mnt/alpine-${{ matrix.os-arch }}
 steps:

diff --git a/action.yml b/action.yml
@@ -12,13 +12,16 @@ inputs:
       hash of the file.
       This should normally be left at the default value.
     required: false
-    default: https://gitlab.alpinelinux.org/api/v4/projects/5/packages/generic/v2.14.7/x86_64/apk.static#!sha256!bdd044e0fd6cc388c5e571e1093efa5f35f7767cc5aa338b0a2576a429009a62
+    default: ''
   arch:
     description: >
-      CPU architecture to emulate using QEMU. Allowed values are: `x86_64` (native), `x86` (native),
-      `aarch64`, `armhf` (armv6 with hard-float), `armv7`, `loongarch64` (available since v3.21), `ppc64le`, `riscv64` (available since v3.20), and `s390x`
+      CPU architecture to emulate using QEMU. Allowed values are: `x86_64` (native on x86_64),
+      `x86` (native on x86_64), `aarch64` (native on aarch64), `armhf` (armv6 with hard-float;
+      native on aarch64), `armv7` (native on aarch64), `loongarch64` (available since v3.21),
+      `ppc64le`, `riscv64` (available since v3.20), `s390x`, or the empty string to use the
+      runner's native architecture.
     required: false
-    default: x86_64
+    default: ''
   branch:
     description: Alpine branch (aka release) to install (e.g. `v3.15`, `latest-stable`, `edge`).
     required: false

diff --git a/binfmts/qemu-i386 b/binfmts/qemu-i386
@@ -0,0 +1,8 @@
+package none
+interpreter /usr/local/bin/qemu-i386
+magic \x7f\x45\x4c\x46\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x03\x00
+offset 0
+mask \xff\xff\xff\xff\xff\xfe\xfe\xfc\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff
+credentials yes
+fix_binary yes
+preserve yes
diff --git a/binfmts/qemu-x86_64 b/binfmts/qemu-x86_64
@@ -0,0 +1,8 @@
+package none
+interpreter /usr/local/bin/qemu-x86_64
+magic \x7f\x45\x4c\x46\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x3e\x00
+offset 0
+mask \xff\xff\xff\xff\xff\xfe\xfe\xfc\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff
+credentials yes
+fix_binary yes
+preserve yes
diff --git a/setup-alpine.sh b/setup-alpine.sh
@@ -84,6 +84,7 @@ needs_emulator() {
 	local host="$(qemu_arch "$(uname -m)")"
 
 	[ "$target" = "$host" ] && return 1
+	[ "$host" = aarch64 ] && [ "$target" = arm ] && return 1
 	[ "$host" = x86_64 ] && [ "$target" = i386 ] && return 1
 	return 0
 }
@@ -133,12 +134,22 @@ mount_bind() {
 
 case "$INPUT_APK_TOOLS_URL" in
 	https://*\#\!sha256\!* | http://*\#\!sha256\!*) ;;  # valid
+	"")
+		# default
+		case "$(uname -m)" in
+			x86_64) INPUT_APK_TOOLS_URL="https://gitlab.alpinelinux.org/api/v4/projects/5/packages/generic/v2.14.7/x86_64/apk.static#!sha256!bdd044e0fd6cc388c5e571e1093efa5f35f7767cc5aa338b0a2576a429009a62" ;;
+			aarch64) INPUT_APK_TOOLS_URL="https://gitlab.alpinelinux.org/api/v4/projects/5/packages/generic/v2.14.7/aarch64/apk.static#!sha256!27a975638ddc95a411c9f17c63383e335da9edf6bb7de2281d950c291a11f878" ;;
+			*) die "Runner has unexpected CPU architecture $(uname -m)" \
+				"Manually configure apk-tools-url for the runner's CPU architecture." ;;
+		esac
+		;;
 	*) die 'Invalid input parameter: apk-tools-url' \
 	       "The value must start with https:// or http:// and end with '#!sha256!' followed by a SHA-256 hash of the file to be downloaded, but got: $INPUT_APK_TOOLS_URL"
 esac
 
 case "$INPUT_ARCH" in
 	x86_64 | x86 | aarch64 | armhf | armv7 | loongarch64 | ppc64le | riscv64 | s390x) ;;  # valid
+	"") INPUT_ARCH="$(uname -m)" ;;  # default
 	*) die 'Invalid input parameter: arch' \
 	       "Expected one of: x86_64, x86, aarch64, armhf, armv7, loongarch64, ppc64le, riscv64, s390x, but got: $INPUT_ARCH."
 esac