diff --git a/core/definitions.mk b/core/definitions.mk
index 2702fc2..99d048b 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -2680,7 +2680,7 @@
 define copy-file-to-target
 @mkdir -p $(dir $@)
 $(hide) rm -f $@
-$(hide) cp $< $@
+$(hide) cp "$<" "$@"
 endef
 
 # The same as copy-file-to-target, but use the local
@@ -2688,7 +2688,7 @@
 define copy-file-to-target-with-cp
 @mkdir -p $(dir $@)
 $(hide) rm -f $@
-$(hide) cp -p $< $@
+$(hide) cp -p "$<" "$@"
 endef
 
 # The same as copy-file-to-target, but strip out "# comment"-style
diff --git a/core/dex_preopt_libart.mk b/core/dex_preopt_libart.mk
index 9616036..de34d88 100644
--- a/core/dex_preopt_libart.mk
+++ b/core/dex_preopt_libart.mk
@@ -11,10 +11,6 @@
 DEX2OAT := $(HOST_OUT_EXECUTABLES)/dex2oatd$(HOST_EXECUTABLE_SUFFIX)
 endif
 
-# Pass special class loader context to skip the classpath and collision check.
-# Should modify build system to pass used libraries properly later.
-DEX2OAT_CLASS_LOADER_CONTEXT := "&"
-
 DEX2OAT_DEPENDENCY += $(DEX2OAT)
 
 # Use the first preloaded-classes file in PRODUCT_COPY_FILES.
@@ -150,7 +146,7 @@
 $(hide) mkdir -p $(dir $(2))
 $(hide) ANDROID_LOG_TAGS="*:e" $(DEX2OAT) \
 	--runtime-arg -Xms$(DEX2OAT_XMS) --runtime-arg -Xmx$(DEX2OAT_XMX) \
-	--class-loader-context=$(DEX2OAT_CLASS_LOADER_CONTEXT) \
+	--class-loader-context=$(PRIVATE_DEX2OAT_CLASS_LOADER_CONTEXT) \
 	--boot-image=$(PRIVATE_DEX_PREOPT_IMAGE_LOCATION) \
 	--dex-file=$(1) \
 	--dex-location=$(PRIVATE_DEX_LOCATION) \
diff --git a/core/setup_one_odex.mk b/core/setup_one_odex.mk
index f0ffe81..e0d9926 100644
--- a/core/setup_one_odex.mk
+++ b/core/setup_one_odex.mk
@@ -32,6 +32,10 @@
     $(DEXPREOPT_ONE_FILE_DEPENDENCY_TOOLS) \
     $(my_dex_preopt_image_filename)
 
+# Pass special class loader context to skip the classpath and collision check.
+# Should modify build system to pass used libraries properly later.
+$(my_built_odex): PRIVATE_DEX2OAT_CLASS_LOADER_CONTEXT := \&
+
 my_installed_odex := $(call get-odex-installed-file-path,$($(my_2nd_arch_prefix)DEX2OAT_TARGET_ARCH),$(LOCAL_INSTALLED_MODULE))
 
 my_built_vdex := $(patsubst %.odex,%.vdex,$(my_built_odex))
diff --git a/envsetup.sh b/envsetup.sh
index 25d95f4..991fee3 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -640,11 +640,17 @@
 # Run tapas with one or more app names (from LOCAL_PACKAGE_NAME)
 function tapas()
 {
+    local showHelp="$(echo $* | xargs -n 1 echo | \grep -E '^(help)$' | xargs)"
     local arch="$(echo $* | xargs -n 1 echo | \grep -E '^(arm|x86|mips|armv5|arm64|x86_64|mips64)$' | xargs)"
     local variant="$(echo $* | xargs -n 1 echo | \grep -E '^(user|userdebug|eng)$' | xargs)"
     local density="$(echo $* | xargs -n 1 echo | \grep -E '^(ldpi|mdpi|tvdpi|hdpi|xhdpi|xxhdpi|xxxhdpi|alldpi)$' | xargs)"
     local apps="$(echo $* | xargs -n 1 echo | \grep -E -v '^(user|userdebug|eng|arm|x86|mips|armv5|arm64|x86_64|mips64|ldpi|mdpi|tvdpi|hdpi|xhdpi|xxhdpi|xxxhdpi|alldpi)$' | xargs)"
 
+    if [ "$showHelp" != "" ]; then
+      $(gettop)/build/make/tapasHelp.sh
+      return
+    fi
+
     if [ $(echo $arch | wc -w) -gt 1 ]; then
         echo "tapas: Error: Multiple build archs supplied: $arch"
         return
diff --git a/tapasHelp.sh b/tapasHelp.sh
new file mode 100755
index 0000000..058ac1d
--- /dev/null
+++ b/tapasHelp.sh
@@ -0,0 +1,23 @@
+#!/bin/bash
+
+# locate some directories
+cd "$(dirname $0)"
+SCRIPT_DIR="${PWD}"
+cd ../..
+TOP="${PWD}"
+
+message='usage: tapas [<App1> <App2> ...] [arm|x86|mips|armv5|arm64|x86_64|mips64] [eng|userdebug|user]
+
+tapas selects individual apps to be built by the Android build system. Unlike
+"lunch", "tapas" does not request the building of images for a device.
+Additionally, an app built with "tapas" will have its dex file inside its apk,
+which should cause it to be suitable for installing on any api-compatible
+device. In other words, "tapas" configures the build of unbundled apps.
+
+The names <App1> <App2> ... should match LOCAL_PACKAGE_NAME as defined in an
+Android.mk
+
+The usage of the other arguments matches that of the rest of the platform
+build system and can be found by running `m help`'
+
+echo "$message"
diff --git a/tools/releasetools/blockimgdiff.py b/tools/releasetools/blockimgdiff.py
index b8123c0..c95512d 100644
--- a/tools/releasetools/blockimgdiff.py
+++ b/tools/releasetools/blockimgdiff.py
@@ -717,6 +717,7 @@
       diff_total = len(diff_queue)
       patches = [None] * diff_total
       error_messages = []
+      warning_messages = []
       if sys.stdout.isatty():
         global diff_done
         diff_done = 0
@@ -750,16 +751,34 @@
             with open(tgt_file, "wb") as fd:
               self.tgt.WriteRangeDataToFd(tgt_ranges, fd)
 
+          message = []
           try:
             patch = compute_patch(src_file, tgt_file, imgdiff)
           except ValueError as e:
+            message.append(
+                "Failed to generate %s for %s: tgt=%s, src=%s:\n%s" % (
+                "imgdiff" if imgdiff else "bsdiff",
+                xf.tgt_name if xf.tgt_name == xf.src_name else
+                    xf.tgt_name + " (from " + xf.src_name + ")",
+                xf.tgt_ranges, xf.src_ranges, e.message))
+            # TODO(b/68016761): Better handle the holes in mke2fs created images.
+            if imgdiff:
+              try:
+                patch = compute_patch(src_file, tgt_file, imgdiff=False)
+                message.append(
+                    "Fell back and generated with bsdiff instead for %s" % (
+                    xf.tgt_name,))
+                with lock:
+                  warning_messages.extend(message)
+                del message[:]
+              except ValueError as e:
+                message.append(
+                    "Also failed to generate with bsdiff for %s:\n%s" % (
+                    xf.tgt_name, e.message))
+
+          if message:
             with lock:
-              error_messages.append(
-                  "Failed to generate %s for %s: tgt=%s, src=%s:\n%s" % (
-                      "imgdiff" if imgdiff else "bsdiff",
-                      xf.tgt_name if xf.tgt_name == xf.src_name else
-                          xf.tgt_name + " (from " + xf.src_name + ")",
-                      xf.tgt_ranges, xf.src_ranges, e.message))
+              error_messages.extend(message)
 
           with lock:
             patches[patch_index] = (xf_index, patch)
@@ -781,8 +800,15 @@
       if sys.stdout.isatty():
         print('\n')
 
+      if warning_messages:
+        print('WARNING:')
+        print('\n'.join(warning_messages))
+        print('\n\n\n')
+
       if error_messages:
+        print('ERROR:')
         print('\n'.join(error_messages))
+        print('\n\n\n')
         sys.exit(1)
     else:
       patches = []