add ldconfig.fakechroot and translate symlinks for bit-by-bit identical buildd variant

coverage.sh

@@ -96,6 +96,13 @@ if [ ! -e shared/proxysolver ] || [ proxysolver -nt shared/proxysolver ]; then
 		cp -a /usr/lib/apt/solvers/mmdebstrap-dump-solution shared/proxysolver
 	fi
 fi
+if [ ! -e shared/ldconfig.fakechroot ] || [ ldconfig.fakechroot -nt shared/ldconfig.fakechroot ]; then
+	if [ -e ./ldconfig.fakechroot ]; then
+		cp -a ldconfig.fakechroot shared
+	else
+		cp -a /usr/libexec/mmdebstrap/ldconfig.fakechroot shared/ldconfig.fakechroot
+	fi
+fi
 mkdir -p shared/hooks
 if [ ! -e shared/hooks/setup00-merged-usr.sh ] || [ hooks/setup00-merged-usr.sh -nt shared/hooks/setup00-merged-usr.sh ]; then
 	if [ -e hooks/setup00-merged-usr.sh ]; then
@@ -754,8 +761,10 @@ fi
 runuser -u user -- $CMD --mode=unshare --variant=$variant $DEFAULT_DIST /tmp/debian-chroot-unshare.$format $mirror
 cmp /tmp/debian-chroot-root.$format /tmp/debian-chroot-unshare.$format
 rm /tmp/debian-chroot-unshare.$format
-case $variant in essential|apt|minbase)
-	# /etc/ld.so.cache differs with some variants
+case $variant in essential|apt|minbase|buildd)
+	# variants important and standard differ because permissions drwxr-sr-x
+	# and extended attributes of ./var/log/journal/ cannot be preserved
+	# in fakechroot mode
 	runuser -u user -- $CMD --mode=fakechroot --variant=$variant $DEFAULT_DIST /tmp/debian-chroot-fakechroot.$format $mirror
 	cmp /tmp/debian-chroot-root.$format /tmp/debian-chroot-fakechroot.$format
 	rm /tmp/debian-chroot-fakechroot.$format

ldconfig.fakechroot

@@ -0,0 +1,111 @@
+#!/usr/bin/env python3
+#
+# This script is in the public domain
+#
+# Author: Johannes Schauer Marin Rodrigues <josch@mister-muffin.de>
+#
+# This is command substitution for ldconfig under fakechroot:
+#
+#     export FAKECHROOT_CMD_SUBST=/sbin/ldconfig=/path/to/ldconfig.fakechroot
+#
+# Statically linked binaries cannot work with fakechroot and thus have to be
+# replaced by either /bin/true or a more clever solution like this one. The
+# ldconfig command supports the -r option which allows passing a chroot
+# directory for ldconfig to work in. This can be used to run ldconfig without
+# fakechroot but still let it create /etc/ld.so.cache inside the chroot.
+#
+# Since absolute symlinks are broken without fakechroot to translate them,
+# we read /etc/ld.so.conf and turn all absolute symlink shared libraries into
+# relative ones. At program exit, the original state is restored.
+
+
+import os
+import sys
+import subprocess
+import atexit
+import glob
+from pathlib import Path
+
+symlinks = []
+
+
+def restore_symlinks():
+    for (link, target, atime, mtime) in symlinks:
+        link.unlink()
+        link.symlink_to(target)
+        os.utime(link, times=None, ns=(atime, mtime), follow_symlinks=False)
+
+
+atexit.register(restore_symlinks)
+
+
+def get_libdirs(chroot, configs):
+    res = []
+    for conf in configs:
+        for line in (Path(conf)).read_text().splitlines():
+            line = line.strip()
+            if not line:
+                continue
+            if line.startswith("#"):
+                continue
+            if line.startswith("include "):
+                assert line.startswith("include /")
+                res.extend(
+                    get_libdirs(chroot, chroot.glob(line.removeprefix("include /")))
+                )
+                continue
+            assert line.startswith("/"), line
+            line = line.lstrip("/")
+            if not (chroot / Path(line)).is_dir():
+                continue
+            for f in (chroot / Path(line)).iterdir():
+                if not f.is_symlink():
+                    continue
+                linktarget = f.readlink()
+                # make sure that the linktarget is an absolute path inside the
+                # chroot
+                if not str(linktarget).startswith("/"):
+                    continue
+                if chroot not in linktarget.parents:
+                    continue
+                # store original link so that we can restore it later
+                symlinks.append(
+                    (f, linktarget, f.lstat().st_atime_ns, f.lstat().st_mtime_ns)
+                )
+                # replace absolute symlink by relative link
+                relative = os.path.relpath(linktarget, f.parent)
+                f.unlink()
+                f.symlink_to(relative)
+    return res
+
+
+def main():
+    if "FAKECHROOT_BASE_ORIG" not in os.environ:
+        print("FAKECHROOT_BASE_ORIG is not set", file=sys.stderr)
+        print(
+            "must be executed under fakechroot using FAKECHROOT_CMD_SUBST",
+            file=sys.stderr,
+        )
+        sys.exit(1)
+
+    chroot = Path(os.environ["FAKECHROOT_BASE_ORIG"])
+
+    if not (chroot / "sbin" / "ldconfig").exists():
+        sys.exit(0)
+
+    (chroot / "var" / "cache" / "ldconfig").mkdir(
+        mode=0o700, parents=True, exist_ok=True
+    )
+
+    for d in get_libdirs(chroot, [chroot / "etc" / "ld.so.conf"]):
+        make_relative(d)
+
+    # we add any additional arguments before "-r" such that any other "-r"
+    # option will be overwritten by the one we set
+    subprocess.check_call(
+        [chroot / "sbin" / "ldconfig"] + sys.argv[1:] + ["-r", chroot]
+    )
+
+
+if __name__ == "__main__":
+    main()

mmdebstrap

@@ -2660,28 +2660,15 @@ sub run_prepare {
         # /etc/fakechroot/debootstrap.env and
         # /etc/fakechroot/chroot.env
         {
-            # we add "$@" before "-r" such that any other "-r" options will be
-            # overwritten by the one we set
-            my $escapedroot = shellescape $options->{root};
-            my ($fh, $filename) = tempfile(
-                "mmdebstrap.ldconfig.XXXXXXXXXXXX",
-                UNLINK => 1,
-                TMPDIR => 1
-            );
-            print $fh <<EOF;
-#!/bin/sh
-set -e
-if [ ! -e $escapedroot/sbin/ldconfig ]; then exit 0; fi
-mkdir --mode=700 --parents $escapedroot/var/cache/ldconfig
-$escapedroot/sbin/ldconfig "\$@" -r $escapedroot
-EOF
-            close $fh;
-            chmod 0755, $filename or error "cannot chmod $filename";
+            my $ldconfig = getcwd() . '/ldconfig.fakechroot';
+            if (!-x $ldconfig) {
+                $ldconfig = '/usr/libexec/mmdebstrap/ldconfig.fakechroot';
+            }
             my @fakechrootsubst = ();
             foreach my $d ('/usr/sbin', '/usr/bin', '/sbin', '/bin') {
                 push @fakechrootsubst, "$d/chroot=/usr/sbin/chroot.fakechroot";
                 push @fakechrootsubst, "$d/mkfifo=/bin/true";
-                push @fakechrootsubst, "$d/ldconfig=$filename";
+                push @fakechrootsubst, "$d/ldconfig=$ldconfig";
                 push @fakechrootsubst, "$d/ldd=/usr/bin/ldd.fakechroot";
                 push @fakechrootsubst, "$d/ischroot=/bin/true";
             }