diff --git a/scripts/build-aml-prebuilts.sh b/scripts/build-aml-prebuilts.sh
index eef6149..c60eaa1 100755
--- a/scripts/build-aml-prebuilts.sh
+++ b/scripts/build-aml-prebuilts.sh
@@ -1,5 +1,15 @@
 #!/bin/bash -e
 
+# This is a wrapper around "m" that builds the given modules in multi-arch mode
+# for all architectures supported by Mainline modules. The make (kati) stage is
+# skipped, so the build targets in the arguments can only be Soong modules or
+# intermediate output files - make targets and normal installed paths are not
+# supported.
+#
+# This script is typically used with "sdk" or "module_export" modules, which
+# Soong will install in $OUT_DIR/soong/mainline-sdks (cf
+# PathForMainlineSdksInstall in android/paths.go).
+
 export OUT_DIR=${OUT_DIR:-out}
 
 if [ -e ${OUT_DIR}/soong/.soong.in_make ]; then
@@ -8,11 +18,16 @@
   # expected to be supplied by the .mk files, and that might cause errors in
   # "m --skip-make" below. We therefore default to a different out dir
   # location in that case.
-  AML_OUT_DIR=out-aml
+  AML_OUT_DIR=out/aml
   echo "Avoiding in-make OUT_DIR '${OUT_DIR}' - building in '${AML_OUT_DIR}' instead"
   OUT_DIR=${AML_OUT_DIR}
 fi
 
+if [ ! -e "build/envsetup.sh" ]; then
+  echo "$0 must be run from the top of the tree"
+  exit 1
+fi
+
 source build/envsetup.sh
 
 my_get_build_var() {
@@ -22,13 +37,13 @@
   OUT_DIR=${OUT_DIR}/get_build_var get_build_var "$@"
 }
 
-PLATFORM_SDK_VERSION=$(my_get_build_var PLATFORM_SDK_VERSION)
-PLATFORM_VERSION=$(my_get_build_var PLATFORM_VERSION)
-PLATFORM_VERSION_ALL_CODENAMES=$(my_get_build_var PLATFORM_VERSION_ALL_CODENAMES)
+readonly PLATFORM_SDK_VERSION="$(my_get_build_var PLATFORM_SDK_VERSION)"
+readonly PLATFORM_VERSION="$(my_get_build_var PLATFORM_VERSION)"
+PLATFORM_VERSION_ALL_CODENAMES="$(my_get_build_var PLATFORM_VERSION_ALL_CODENAMES)"
 
 # PLATFORM_VERSION_ALL_CODENAMES is a comma separated list like O,P. We need to
 # turn this into ["O","P"].
-PLATFORM_VERSION_ALL_CODENAMES=${PLATFORM_VERSION_ALL_CODENAMES/,/'","'}
+PLATFORM_VERSION_ALL_CODENAMES="${PLATFORM_VERSION_ALL_CODENAMES/,/'","'}"
 PLATFORM_VERSION_ALL_CODENAMES="[\"${PLATFORM_VERSION_ALL_CODENAMES}\"]"
 
 # Logic from build/make/core/goma.mk
@@ -46,11 +61,16 @@
   USE_GOMA=false
 fi
 
-SOONG_OUT=${OUT_DIR}/soong
+readonly SOONG_OUT=${OUT_DIR}/soong
 mkdir -p ${SOONG_OUT}
-SOONG_VARS=${SOONG_OUT}/soong.variables
+readonly SOONG_VARS=${SOONG_OUT}/soong.variables
 
-# We enable bionic linux builds as ART also needs prebuilts for it.
+# Aml_abis: true
+#   -  This flag configures Soong to compile for all architectures required for
+#      Mainline modules.
+# CrossHost: linux_bionic
+# CrossHostArch: x86_64
+#   -  Enable Bionic on host as ART needs prebuilts for it.
 cat > ${SOONG_VARS}.new << EOF
 {
     "Platform_sdk_version": ${PLATFORM_SDK_VERSION},
@@ -79,4 +99,6 @@
 # We use force building LLVM components flag (even though we actually don't
 # compile them) because we don't have bionic host prebuilts
 # for them.
-FORCE_BUILD_LLVM_COMPONENTS=true m --skip-make "$@"
+export FORCE_BUILD_LLVM_COMPONENTS=true
+
+m --skip-make "$@"
diff --git a/scripts/build-mainline-modules.sh b/scripts/build-mainline-modules.sh
index 79e40dd..826779b 100755
--- a/scripts/build-mainline-modules.sh
+++ b/scripts/build-mainline-modules.sh
@@ -1,4 +1,4 @@
-#!/bin/bash -ex
+#!/bin/bash -e
 
 # Non exhaustive list of modules where we want prebuilts. More can be added as
 # needed.
@@ -22,42 +22,45 @@
 
 # We want to create apex modules for all supported architectures.
 PRODUCTS=(
-    aosp_arm
-    aosp_arm64
-    aosp_x86
-    aosp_x86_64
+  aosp_arm
+  aosp_arm64
+  aosp_x86
+  aosp_x86_64
 )
 
 if [ ! -e "build/make/core/Makefile" ]; then
-    echo "$0 must be run from the top of the tree"
-    exit 1
+  echo "$0 must be run from the top of the tree"
+  exit 1
 fi
 
+echo_and_run() {
+  echo "$*"
+  "$@"
+}
+
 OUT_DIR=$(source build/envsetup.sh > /dev/null; TARGET_PRODUCT= get_build_var OUT_DIR)
 DIST_DIR=$(source build/envsetup.sh > /dev/null; TARGET_PRODUCT= get_build_var DIST_DIR)
 
 for product in "${PRODUCTS[@]}"; do
-    build/soong/soong_ui.bash --make-mode $@ \
-        TARGET_PRODUCT=${product} \
-        ${MAINLINE_MODULES[@]}
+  echo_and_run build/soong/soong_ui.bash --make-mode $@ \
+    TARGET_PRODUCT=${product} \
+    ${MAINLINE_MODULES[@]}
 
-    PRODUCT_OUT=$(source build/envsetup.sh > /dev/null; TARGET_PRODUCT=${product} get_build_var PRODUCT_OUT)
-    TARGET_ARCH=$(source build/envsetup.sh > /dev/null; TARGET_PRODUCT=${product} get_build_var TARGET_ARCH)
-    rm -rf ${DIST_DIR}/${TARGET_ARCH}/
-    mkdir -p ${DIST_DIR}/${TARGET_ARCH}/
-    for module in "${MAINLINE_MODULES[@]}"; do
-      cp ${PWD}/${PRODUCT_OUT}/system/apex/${module}.apex ${DIST_DIR}/${TARGET_ARCH}/
-    done
+  PRODUCT_OUT=$(source build/envsetup.sh > /dev/null; TARGET_PRODUCT=${product} get_build_var PRODUCT_OUT)
+  TARGET_ARCH=$(source build/envsetup.sh > /dev/null; TARGET_PRODUCT=${product} get_build_var TARGET_ARCH)
+  rm -rf ${DIST_DIR}/${TARGET_ARCH}/
+  mkdir -p ${DIST_DIR}/${TARGET_ARCH}/
+  for module in "${MAINLINE_MODULES[@]}"; do
+    echo_and_run cp ${PWD}/${PRODUCT_OUT}/system/apex/${module}.apex ${DIST_DIR}/${TARGET_ARCH}/
+  done
 done
 
 
 # Create multi-archs SDKs in a different out directory. The multi-arch script
-# uses soong directly and therefore needs its own directory that doesn't clash
-# with make.
-export OUT_DIR=${OUT_DIR}/aml/
-for sdk in "${MODULES_SDK_AND_EXPORTS[@]}"; do
-    build/soong/scripts/build-aml-prebuilts.sh ${sdk}
-done
+# uses Soong in --skip-make mode which cannot use the same directory as normal
+# mode with make.
+export OUT_DIR=${OUT_DIR}/aml
+echo_and_run build/soong/scripts/build-aml-prebuilts.sh ${MODULES_SDK_AND_EXPORTS[@]}
 
 rm -rf ${DIST_DIR}/mainline-sdks
-cp -R ${OUT_DIR}/soong/mainline-sdks ${DIST_DIR}
+echo_and_run cp -R ${OUT_DIR}/soong/mainline-sdks ${DIST_DIR}