From d0e97fa1ed17e71c1ab9d08bc7e530414f52590a Mon Sep 17 00:00:00 2001
From: Mikael Voss <mvs@nyantec.com>
Date: Fri, 29 Nov 2024 16:41:23 +0100
Subject: [PATCH] builders: Enable user mode emulation for RISC-V and ARM

---
 pkgs/build-worker-oci/default.nix   |  3 ++-
 pkgs/build-worker-oci/entrypoint.sh | 12 ++++++++++++
 pkgs/overlay.nix                    |  6 +++++-
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/pkgs/build-worker-oci/default.nix b/pkgs/build-worker-oci/default.nix
index 958a6ae..06ce68f 100644
--- a/pkgs/build-worker-oci/default.nix
+++ b/pkgs/build-worker-oci/default.nix
@@ -6,6 +6,7 @@
   bash,
   gnused,
   util-linux,
+  qemu-user
 }:
 
 dockerTools.buildLayeredImage {
@@ -20,7 +21,7 @@ dockerTools.buildLayeredImage {
 
   enableFakechroot = true;
 
-  contents = [ openssh util-linux bash gnused ];
+  contents = [ openssh util-linux bash gnused qemu-user ];
 
   config.Cmd = [ "/entrypoint.sh" ];
 
diff --git a/pkgs/build-worker-oci/entrypoint.sh b/pkgs/build-worker-oci/entrypoint.sh
index 541bd13..4bf14fc 100644
--- a/pkgs/build-worker-oci/entrypoint.sh
+++ b/pkgs/build-worker-oci/entrypoint.sh
@@ -26,4 +26,16 @@ cp /root/nix.conf /etc/nix/nix.conf
 /bin/mount -t overlay overlay -o lowerdir=/nix,upperdir=/mnt/data/nix-store,workdir=/mnt/data/workdir /nix
 /bin/mount --bind /mnt/data/tmp /tmp
 
+# Register QEMU binaries for user mode emulation
+aarch64_magic='\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xb7\x00'
+aarch64_mask='\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff'
+
+riscv64_magic='\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xf3\x00'
+riscv64_mask='\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff'
+
+execPath() { readlink -f "$(which "$1")" }
+
+echo ":qemu-aarch64:M::$aarch64_magic:$aarch64_mask:$(execPath qemu-aarch64):POCF" >/proc/sys/fs/binfmt_misc/register
+echo ":qemu-riscv64:M::$riscv64_magic:$riscv64_mask:$(execPath qemu-riscv64):POCF" >/proc/sys/fs/binfmt_misc/register
+
 /root/.nix-profile/bin/sshd -D -f /root/sshd_config
diff --git a/pkgs/overlay.nix b/pkgs/overlay.nix
index 5a40d24..e941e12 100644
--- a/pkgs/overlay.nix
+++ b/pkgs/overlay.nix
@@ -2,7 +2,11 @@ final: prev: {
   nyastodon = final.callPackage ./nyastodon/default.nix {};
   upgrade-system = final.callPackage ./upgrade-system/default.nix {};
   update-nixfiles = final.callPackage ./update-nixfiles/default.nix {};
-  build-worker-oci = final.callPackage ./build-worker-oci/default.nix {};
+  build-worker-oci = final.callPackage ./build-worker-oci/default.nix {
+    qemu-user = final.pkgsStatic.qemu-user.override {
+      hostCpuTargets = [ "aarch64-linux-user" "riscv64-linux-user" ];
+    };
+  };
   librespeed-rust = final.callPackage ./librespeed-rust/default.nix {};
   librespeed-go = final.callPackage ./librespeed-go/default.nix {};
   akkoma-fe-domi = final.callPackage ./akkoma-fe-domi/default.nix {};