Support for dynamically-linked busybox

README.md

@@ -59,7 +59,7 @@ Your host system will need to satisfy some prerequisites:
 * You need Python 3.3 or higher.
 * QEMU 1.6 or higher is recommended.  QEMU 1.4 and 1.5 are partially supported using a rather ugly kludge.
   * You will have a much better experience if KVM is enabled.  That means that you should be on bare metal with hardware virtualization (VT-x or SVM) enabled or in a VM that supports nested virtualization.  On some Linux distributions, you may need to be a member of the "kvm" group.  Using VirtualBox or most VPS providers will fall back to emulation.
-* Depending on the options you use, you may need a statically linked `busybox` binary somewhere in your path.
+* Depending on the options you use, you may need a `busybox` binary somewhere in your path.
 
 Once you have such a kernel, run one of:
 

virtme/mkinitramfs.py

@@ -12,6 +12,7 @@
 import os.path
 import shlex
 import itertools
+import subprocess
 from . import cpiowriter
 
 def make_base_layout(cw):
@@ -22,6 +23,10 @@ def make_base_layout(cw):
     cw.symlink(b'bin', b'sbin')
     cw.symlink(b'lib', b'lib64')
 
+    # Hack to support systems that expect some form of /usr at boot
+    # (e.g. with a dynamically-linked busybox with libs in /usr/lib)
+    cw.symlink(b'/', b'usr')
+
 def make_dev_nodes(cw):
     cw.mkchardev(b'dev/null', (1, 3), mode=0o666)
     cw.mkchardev(b'dev/kmsg', (1, 11), mode=0o666)
@@ -31,6 +36,31 @@ def install_busybox(cw, config):
     with open(config.busybox, 'rb') as busybox:
         cw.write_file(name=b'bin/busybox', body=busybox, mode=0o755)
 
+    # HACK: install libraries if busybox is dynamically linked
+    try:
+        bbldd = subprocess.check_output(['ldd', config.busybox])
+    except subprocess.CalledProcessError:
+        # assume we're working with a statically-linked busybox
+        pass
+    else:
+        for line in bbldd.splitlines():
+            line = line.decode('ascii').strip()
+            parts = line.split()
+            if 'linux-vdso.so' in parts[0]:
+                # don't need to bother with VDSO
+                continue
+            elif parts[1] == '=>' and parts[2][0] == '/':
+                # normal libs are of the form 'libfoo.so => /path/to/libfoo.so (0xdeadbeef)'
+                hostpath = parts[2]
+            elif parts[0][0] == '/':
+                # ld.so has the absolute path as the first field
+                hostpath = parts[0]
+            else:
+                raise ValueError("can't handle line from `ldd busybox`: '%s'" % line)
+            guestpath  = 'lib/%s' % os.path.basename(hostpath)
+            with open(hostpath, 'rb') as lib:
+                cw.write_file(name=guestpath.encode('ascii'), body=lib, mode=0o755)
+
     for tool in ('sh', 'mount', 'umount', 'switch_root', 'sleep', 'mkdir',
                  'mknod', 'insmod', 'cp', 'cat'):
         cw.symlink(b'busybox', ('bin/%s' % tool).encode('ascii'))