diff --git a/configure.ac b/configure.ac
index acf5ac7ce..bf18abea3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -10,8 +10,8 @@ AC_CANONICAL_HOST
 
 # Construct a Nix system name (like "i686-linux").
 AC_MSG_CHECKING([for the canonical Nix system name])
-cpu_name=$(uname -p | tr 'A-Z ' 'a-z_')
-machine_name=$(uname -m | tr 'A-Z ' 'a-z_')
+cpu_name=$(uname -p | tr 'ABCDEFGHIJKLMNOPQRSTUVWXYZ ' 'abcdefghijklmnopqrstuvwxyz_')
+machine_name=$(uname -m | tr 'ABCDEFGHIJKLMNOPQRSTUVWXYZ ' 'abcdefghijklmnopqrstuvwxyz_')
 
 case $machine_name in
     i*86)
@@ -30,7 +30,7 @@ case $machine_name in
         ;;
 esac
 
-sys_name=$(uname -s | tr 'A-Z ' 'a-z_')
+sys_name=$(uname -s | tr 'ABCDEFGHIJKLMNOPQRSTUVWXYZ ' 'abcdefghijklmnopqrstuvwxyz_')
 
 case $sys_name in
     cygwin*)
@@ -128,6 +128,10 @@ AC_CHECK_HEADERS([locale], [], [], [])
 AC_LANG_POP(C++)
 
 
+# Check for <err.h>.
+AC_CHECK_HEADER([err.h], [], [bsddiff_compat_include="-Icompat-include"])
+AC_SUBST([bsddiff_compat_include])
+
 # Check whether we have the personality() syscall, which allows us to
 # do i686-linux builds on x86_64-linux machines.
 AC_CHECK_HEADERS([sys/personality.h])
diff --git a/nix.conf.example b/nix.conf.example
index e17cf3c25..7063bed54 100644
--- a/nix.conf.example
+++ b/nix.conf.example
@@ -59,6 +59,17 @@
 #build-max-jobs = 1
 
 
+### Option `build-cores'
+#
+# This option defines the number of CPU cores to utilize in parallel
+# within a build job, i.e. by passing an appropriate `-jN' flag to GNU
+# make. The default is 1, meaning that parallel building within jobs
+# is disabled.  Passing the special value `0' causes Nix to try and
+# auto-detect the number of available cores on the local host.  This
+# setting can be overridden using the `--cores' command line switch.
+#build-cores = 1
+
+
 ### Option `build-max-silent-time'
 #
 # This option defines the maximum number of seconds that a builder can
diff --git a/scripts/generate-patches.pl.in b/scripts/generate-patches.pl.in
index 148b7d81f..dba647350 100755
--- a/scripts/generate-patches.pl.in
+++ b/scripts/generate-patches.pl.in
@@ -20,11 +20,11 @@ die unless scalar @ARGV == 5;
 
 my $hashAlgo = "sha256";
 
-my $cacheDir = $ARGV[0];
+my $narDir = $ARGV[0];
 my $patchesDir = $ARGV[1];
 my $patchesURL = $ARGV[2];
-my $srcDir = $ARGV[3];
-my $dstDir = $ARGV[4];
+my $srcManifest = $ARGV[3];
+my $dstManifest = $ARGV[4];
 
 my $tmpDir = tempdir("nix-generate-patches.XXXXXX", CLEANUP => 1, TMPDIR => 1)
     or die "cannot create a temporary directory";
@@ -41,10 +41,10 @@ my %dstNarFiles;
 my %dstLocalPaths;
 my %dstPatches;
 
-readManifest "$srcDir/MANIFEST",
+readManifest "$srcManifest",
     \%srcNarFiles, \%srcLocalPaths, \%srcPatches;
 
-readManifest "$dstDir/MANIFEST",
+readManifest "$dstManifest",
     \%dstNarFiles, \%dstLocalPaths, \%dstPatches;
 
 
@@ -55,8 +55,7 @@ sub findOutputPaths {
     
     foreach my $p (keys %{$narFiles}) {
 
-        # Ignore store expressions.
-        next if ($p =~ /\.store$/);
+        # Ignore derivations.
         next if ($p =~ /\.drv$/);
         
         # Ignore builders (too much ambiguity -- they're all called
@@ -65,7 +64,7 @@ sub findOutputPaths {
         next if ($p =~ /\.patch$/);
         
         # Don't bother including tar files etc.
-        next if ($p =~ /\.tar\.(gz|bz2)$/ || $p =~ /\.zip$/ || $p =~ /\.bin$/);
+        next if ($p =~ /\.tar$/ || $p =~ /\.tar\.(gz|bz2|Z|lzma|xz)$/ || $p =~ /\.zip$/ || $p =~ /\.bin$/ || $p =~ /\.tgz$/ || $p =~ /\.rpm$/ || $p =~ /cvs-export$/ || $p =~ /fetchhg$/);
 
         $outPaths{$p} = 1;
     }
@@ -85,6 +84,7 @@ sub getNameVersion {
     $p =~ /\/[0-9a-z]+((?:-[a-zA-Z][^\/-]*)+)([^\/]*)$/;
     my $name = $1;
     my $version = $2;
+    return undef unless defined $name && defined $version;
     $name =~ s/^-//;
     $version =~ s/^-//;
     return ($name, $version);
@@ -112,14 +112,14 @@ sub getNarBz2 {
     my $storePath = shift;
     
     my $narFileList = $$narFiles{$storePath};
-    die "missing store expression $storePath" unless defined $narFileList;
+    die "missing path $storePath" unless defined $narFileList;
 
     my $narFile = @{$narFileList}[0];
     die unless defined $narFile;
 
     $narFile->{url} =~ /\/([^\/]+)$/;
     die unless defined $1;
-    return "$cacheDir/$1";
+    return "$narDir/$1";
 }
 
 
@@ -213,6 +213,7 @@ foreach my $p (keys %dstOutPaths) {
     # this path.
 
     (my $name, my $version) = getNameVersion $p;
+    next unless defined $name && defined $version;
 
     my @closest = ();
     my $closestVersion;
@@ -222,6 +223,8 @@ foreach my $p (keys %dstOutPaths) {
 
     foreach my $q (keys %srcOutPaths) {
         (my $name2, my $version2) = getNameVersion $q;
+	next unless defined $name2 && defined $version2;
+
         if ($name eq $name2) {
 
             # If the sizes differ too much, then skip.  This
@@ -241,11 +244,11 @@ foreach my $p (keys %dstOutPaths) {
             # If the numbers of weighted uses differ too much, then
             # skip.  This disambiguates between, e.g., the bootstrap
             # GCC and the final GCC in Nixpkgs.
-            my $srcUses = computeUses \%srcNarFiles, $q;
-            my $dstUses = computeUses \%dstNarFiles, $p;
-            $ratio = $srcUses / $dstUses;
-            $ratio = 1 / $ratio if $ratio < 1;
-            print "  USE $srcUses $dstUses $ratio $q\n";
+#            my $srcUses = computeUses \%srcNarFiles, $q;
+#            my $dstUses = computeUses \%dstNarFiles, $p;
+#            $ratio = $srcUses / $dstUses;
+#            $ratio = 1 / $ratio if $ratio < 1;
+#            print "  USE $srcUses $dstUses $ratio $q\n";
             
 #            if ($ratio >= 2) {
 #                print "  SKIPPING $q due to use ratio $ratio ($srcUses $dstUses)\n";
@@ -288,6 +291,11 @@ foreach my $p (keys %dstOutPaths) {
         my $srcNarBz2 = getNarBz2 \%srcNarFiles, $closest;
         my $dstNarBz2 = getNarBz2 \%dstNarFiles, $p;
 
+        if (! -f $srcNarBz2) {
+            warn "patch source archive $srcNarBz2 is missing\n";
+            next;
+        }
+
         system("@bunzip2@ < $srcNarBz2 > $tmpDir/A") == 0
             or die "cannot unpack $srcNarBz2";
 
@@ -404,5 +412,5 @@ do {
 
 
 # Rewrite the manifest of the destination (with the new patches).
-writeManifest "$dstDir/MANIFEST",
+writeManifest "${dstManifest}",
     \%dstNarFiles, \%dstPatches;
diff --git a/src/bsdiff-4.3/Makefile.am b/src/bsdiff-4.3/Makefile.am
index 4b3af0783..57970bc55 100644
--- a/src/bsdiff-4.3/Makefile.am
+++ b/src/bsdiff-4.3/Makefile.am
@@ -1,3 +1,5 @@
+EXTRA_DIST = compat-include
+
 libexec_PROGRAMS = bsdiff bspatch
 
 bsdiff_SOURCES = bsdiff.c
@@ -8,4 +10,4 @@ bspatch_SOURCES = bspatch.c
 
 bspatch_LDADD = ${bzip2_lib}
 
-AM_CFLAGS = -O3 ${bzip2_include}
+AM_CFLAGS = -O3 ${bzip2_include} ${bsddiff_compat_include}
diff --git a/src/bsdiff-4.3/compat-include/err.h b/src/bsdiff-4.3/compat-include/err.h
new file mode 100644
index 000000000..a851ded6f
--- /dev/null
+++ b/src/bsdiff-4.3/compat-include/err.h
@@ -0,0 +1,12 @@
+/* Simulate BSD's <err.h> functionality. */
+
+#ifndef COMPAT_ERR_H_INCLUDED
+#define COMPAT_ERR_H_INCLUDED 1
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define err(rc,...)  do { fprintf(stderr,__VA_ARGS__); exit(rc); } while(0)
+#define errx(rc,...) do { fprintf(stderr,__VA_ARGS__); exit(rc); } while(0)
+
+#endif
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index eb1d8d432..96bda43a3 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -750,13 +750,15 @@ void ExprOpImpl::eval(EvalState & state, Env & env, Value & v)
 
 void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
 {
-    Value v2;
-    state.evalAttrs(env, e1, v2);
-        
-    state.cloneAttrs(v2, v);
-        
+    Value v1, v2;
+    state.evalAttrs(env, e1, v1);
     state.evalAttrs(env, e2, v2);
-    
+
+    if (v1.attrs->size() == 0) { v = v2; return; }
+    if (v2.attrs->size() == 0) { v = v1; return; }
+
+    state.cloneAttrs(v1, v);
+
     foreach (Bindings::iterator, i, *v2.attrs) {
         Attr & a = (*v.attrs)[i->first];
         mkCopy(a.value, i->second.value);
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 42c858611..68f66acc7 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -788,13 +788,13 @@ static void prim_intersectAttrs(EvalState & state, Value * * args, Value & v)
     state.forceAttrs(*args[1]);
         
     state.mkAttrs(v);
-    
-    foreach (Bindings::iterator, i, *args[1]->attrs) {
-        Bindings::iterator j = args[0]->attrs->find(i->first);
-        if (j != args[0]->attrs->end()) {
-            Attr & a = (*v.attrs)[i->first];
-            mkCopy(a.value, i->second.value);
-            a.pos = i->second.pos;
+
+    foreach (Bindings::iterator, i, *args[0]->attrs) {
+        Bindings::iterator j = args[1]->attrs->find(i->first);
+        if (j != args[1]->attrs->end()) {
+            Attr & a = (*v.attrs)[j->first];
+            mkCopy(a.value, j->second.value);
+            a.pos = j->second.pos;
         }
     }
 }
diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index 3fbec4b52..eddc4e64b 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -135,6 +135,7 @@ static void initAndRun(int argc, char * * argv)
     /* Get some settings from the configuration file. */
     thisSystem = querySetting("system", SYSTEM);
     maxBuildJobs = queryIntSetting("build-max-jobs", 1);
+    buildCores = queryIntSetting("build-cores", 1);
     maxSilentTime = queryIntSetting("build-max-silent-time", 0);
 
     /* Catch SIGINT. */
@@ -226,6 +227,8 @@ static void initAndRun(int argc, char * * argv)
             tryFallback = true;
         else if (arg == "--max-jobs" || arg == "-j")
             maxBuildJobs = getIntArg<unsigned int>(arg, i, args.end());
+        else if (arg == "--cores")
+            buildCores = getIntArg<unsigned int>(arg, i, args.end());
         else if (arg == "--readonly-mode")
             readOnlyMode = true;
         else if (arg == "--max-silent-time")
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 5818aa51d..6f0276244 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -25,6 +25,7 @@
 #include <unistd.h>
 #include <errno.h>
 #include <stdio.h>
+#include <cstring>
 
 #include <pwd.h>
 #include <grp.h>
@@ -1427,6 +1428,9 @@ void DerivationGoal::startBuilder()
        in the store or in the build directory). */
     env["NIX_STORE"] = nixStore;
 
+    /* The maximum number of cores to utilize for parallel building. */
+    env["NIX_BUILD_CORES"] = (format("%d") % buildCores).str();
+
     /* Add all bindings specified in the derivation. */
     foreach (StringPairs::iterator, i, drv.env)
         env[i->first] = i->second;
@@ -2654,6 +2658,7 @@ void Worker::waitForInput()
         timeout.tv_sec = std::max((time_t) 0, lastWokenUp + wakeUpInterval - before);
     } else lastWokenUp = 0;
 
+    using namespace std;
     /* Use select() to wait for the input side of any logger pipe to
        become `available'.  Note that `available' (i.e., non-blocking)
        includes EOF. */
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index cc0e44e8e..75d2f69c2 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -22,6 +22,7 @@ bool keepGoing = false;
 bool tryFallback = false;
 Verbosity buildVerbosity = lvlInfo;
 unsigned int maxBuildJobs = 1;
+unsigned int buildCores = 1;
 bool readOnlyMode = false;
 string thisSystem = "unset";
 time_t maxSilentTime = 0;
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index d3388e309..a74a741d6 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -55,6 +55,11 @@ extern Verbosity buildVerbosity;
 /* Maximum number of parallel build jobs.  0 means unlimited. */
 extern unsigned int maxBuildJobs;
 
+/* Number of CPU cores to utilize in parallel within a build, i.e. by passing
+   this number to Make via '-j'. 0 means that the number of actual CPU cores on
+   the local host ought to be auto-detected. */
+extern unsigned int buildCores;
+
 /* Read-only mode.  Don't copy stuff to the store, don't change the
    database. */
 extern bool readOnlyMode;
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 334ad95cf..93319ebb8 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -13,6 +13,7 @@
 
 #include <iostream>
 #include <unistd.h>
+#include <cstring>
 
 
 namespace nix {
@@ -158,6 +159,7 @@ void RemoteStore::connectToDaemon()
     addr.sun_family = AF_UNIX;
     if (socketPathRel.size() >= sizeof(addr.sun_path))
         throw Error(format("socket path `%1%' is too long") % socketPathRel);
+    using namespace std;
     strcpy(addr.sun_path, socketPathRel.c_str());
     
     if (connect(fdSocket, (struct sockaddr *) &addr, sizeof(addr)) == -1)
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index e0c41a58d..9540720fe 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -12,6 +12,7 @@
 #include <sys/types.h>
 #include <fcntl.h>
 #include <unistd.h>
+#include <limits.h>
 
 #include "util.hh"
 
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index ca67119e9..a67ce243a 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -247,11 +247,12 @@ static DrvInfos filterBySelector(EvalState & state, const DrvInfos & allElems,
         }
 
         /* If `newestOnly', if a selector matches multiple derivations
-           with the same name, pick the one with the highest priority.
-           If there are multiple derivations with the same priority,
-           pick the one with the highest version.  If there are
-           multiple derivations with the same priority and name and
-           version, then pick the first one. */
+           with the same name, pick the one matching the current
+           system.  If there are still multiple derivations, pick the
+           one with the highest priority.  If there are still multiple
+           derivations, pick the one with the highest version.
+           Finally, if there are still multiple derivations,
+           arbitrarily pick the first one. */
         if (newestOnly) {
 
             /* Map from package names to derivations. */
@@ -266,7 +267,12 @@ static DrvInfos filterBySelector(EvalState & state, const DrvInfos & allElems,
                 Newest::iterator k = newest.find(drvName.name);
                 
                 if (k != newest.end()) {
-                    d = comparePriorities(state, j->first, k->second.first);
+                    d = j->first.system == k->second.first.system ? 0 :
+                        j->first.system == thisSystem ? 1 :
+                        k->second.first.system == thisSystem ? -1 : 0;
+                    printMsg(lvlError, format("%1% %2% %3% %4%") % j->first.system % k->second.first.system % thisSystem % d);
+                    if (d == 0)
+                        d = comparePriorities(state, j->first, k->second.first);
                     if (d == 0)
                         d = compareVersions(drvName.version, DrvName(k->second.first.name).version);
                 }
@@ -1230,7 +1236,7 @@ void run(Strings args)
     
     globals.instSource.type = srcUnknown;
     globals.instSource.nixExprPath = getDefNixExprPath();
-    globals.instSource.systemFilter = thisSystem;
+    globals.instSource.systemFilter = "*";
     
     globals.dryRun = false;
     globals.preserveInstalled = false;
diff --git a/src/nix-worker/nix-worker.cc b/src/nix-worker/nix-worker.cc
index d41877e88..b292b83ed 100644
--- a/src/nix-worker/nix-worker.cc
+++ b/src/nix-worker/nix-worker.cc
@@ -7,6 +7,7 @@
 #include "globals.hh"
 
 #include <iostream>
+#include <cstring>
 #include <unistd.h>
 #include <signal.h>
 #include <sys/types.h>
@@ -111,6 +112,7 @@ static bool isFarSideClosed(int socket)
    time and wouldn't have to worry about races. */
 static void sigPollHandler(int sigNo)
 {
+    using namespace std;
     try {
         /* Check that the far side actually closed.  We're still
            getting spurious signals every once in a while.  I.e.,
diff --git a/tests/build-hook.hook.sh b/tests/build-hook.hook.sh
index 18eba283e..83fa3bf78 100755
--- a/tests/build-hook.hook.sh
+++ b/tests/build-hook.hook.sh
@@ -6,11 +6,11 @@ drv=$4
 
 echo "HOOK for $drv" >&2
 
-outPath=$(sed 's/Derive(\[("out",\"\([^\"]*\)\".*/\1/' $drv)
+outPath=`sed 's/Derive(\[("out",\"\([^\"]*\)\".*/\1/' $drv`
 
 echo "output path is $outPath" >&2
 
-if $(echo $outPath | grep -q input-1); then
+if `echo $outPath | grep -q input-1`; then
     echo "# accept" >&2
     read x
     echo "got $x"