From 9e0584c9b36317a290fe6ba212eac53f94303193 Mon Sep 17 00:00:00 2001
From: Renato Aguiar <renato@renatoaguiar.net>
Date: Mon, 17 Feb 2020 16:19:10 -0800
Subject: [PATCH] Avoid copying qemu-static to rootfs

Use fix binary flag (F) to load binfmt interpreter (qemu-static) on
register, so it doesn't need to be copied to chroot.

This requires kernel >= 4.9.
---
 lib.sh.in | 18 +-----------------
 1 file changed, 1 insertion(+), 17 deletions(-)

diff --git a/lib.sh.in b/lib.sh.in
index 55cb73b..0af2805 100644
--- a/lib.sh.in
+++ b/lib.sh.in
@@ -134,11 +134,6 @@ cleanup_chroot() {
 
     # Un-Mount the pseudofs mounts if they were mounted
     umount_pseudofs
-
-    # If a QEMU binary was copied in, remove that as well
-    if [ -x "$ROOTFS/usr/bin/$QEMU_BIN" ] ; then
-        rm "$ROOTFS/usr/bin/$QEMU_BIN"
-    fi
 }
 
 # TODO: Figure out how to register the binfmt for x86_64 and for i686
@@ -232,18 +227,7 @@ register_binfmt() {
 
     # Only register if the map is incomplete
     if [ ! -f /proc/sys/fs/binfmt_misc/qemu-$_cpu ] ; then
-        echo ":qemu-$_cpu:M::$_magic:$_mask:/usr/bin/$QEMU_BIN:" > /proc/sys/fs/binfmt_misc/register 2>/dev/null
-    fi
-
-    # If the static binary isn't in the chroot then the chroot will
-    # fail.  The kernel knows about the map but without the static
-    # version there's no interpreter in the chroot, only the
-    # dynamically linked one in the host.  To simplify things we just
-    # use the static one always and make sure it shows up at the same
-    # place in the host and the chroot.
-    if [ ! -x "$ROOTFS/usr/bin/$QEMU_BIN" ] ; then
-        install -m755 -D "$(which "$QEMU_BIN")" "$ROOTFS/usr/bin/$QEMU_BIN" ||
-            die "Could not install $QEMU_BIN to $ROOTFS/usr/bin/"
+        echo ":qemu-$_cpu:M::$_magic:$_mask:/usr/bin/$QEMU_BIN:F" > /proc/sys/fs/binfmt_misc/register 2>/dev/null
     fi
 }