--- a/qt5.SlackBuild	2021-03-14 11:02:19.928819259 +0200
+++ b/qt5.SlackBuild	2021-03-14 11:08:30.297082225 +0200
@@ -81,6 +81,16 @@
   SLKCFLAGS="-O2 -march=armv7-a -mfpu=vfpv3-d16 -fno-strict-volatile-bitfields"
   SLKLDFLAGS=""
   LIBDIRSUFFIX=""
+elif [ "$ARCH" = "aarch64" ]; then
+  SLKCFLAGS="-O2 -fPIC"
+  SLKLDFLAGS=""
+  SLKLDFLAGS="-L/usr/lib64"
+  LIBDIRSUFFIX="64"
+elif [ "$ARCH" = "riscv64" ]; then
+  SLKCFLAGS="-O2 -fPIC"
+  SLKLDFLAGS=""
+  SLKLDFLAGS="-L/usr/lib64"
+  LIBDIRSUFFIX="64"
 else
   SLKCFLAGS="-O2"
   SLKLDFLAGS=""
@@ -130,6 +140,8 @@
 # See also https://bugzilla.redhat.com/1704474
 cd qtbase
   zcat $CWD/patches/qt5.qtbase_cmake_isystem_includes.patch.gz | patch -p1 --verbose || exit 1
+  # RISC-V: must use -pthread to link libatomic
+  xzcat $CWD/patches/qtbase-everywhere-src-5.12.4-pthread.patch.xz | patch -p1 --verbose || exit 1
 cd - 1>/dev/null
 
 # Fix sandbox functions for glibc-2.33:
@@ -146,6 +158,19 @@
   unset TAG
 fi
 
+if [[ "$ARCH" == "aarch64" || "$ARCH" == "riscv64" ]]; then
+  EXTRACONF="-no-sse2 \
+             -no-sse3 \
+             -no-ssse3 \
+             -no-sse4.1 \
+             -no-sse4.2 \
+             -no-avx \
+             -no-avx2 \
+             -no-feature-getentropy"
+else
+  EXTRACONF=" "
+fi
+
 # Use our custom compiler and linker flags:
 sed -e "s|^\(QMAKE_CFLAGS_RELEASE.*\)|\1 ${SLKCFLAGS}|" \
   -i qtbase/mkspecs/common/gcc-base.conf || exit 1
@@ -210,6 +235,7 @@
   ${FFMPEG_OPTION} \
   ${PULSEAUDIO_OPTION} \
   ${RELOCATIONS} \
+  ${EXTRACONF} \
   -no-pch
   # No-precompiled-headers is ccache-friendly.