diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3dc5c91d..69153095 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -410,8 +410,8 @@ jobs:
       # for cross build, cross-setup.sh takes care of the toolchain
       if: matrix.os == 'ubuntu-20.04' && matrix.arch == 'native'
       run: |
-        sudo ./cross/setup-focal-proposed.sh
-        sudo apt-get update && sudo apt-get install -y clang-13 lld-13
+        sudo ./cross/setup-apt-llvm-org.sh
+        sudo apt-get update && sudo apt-get install -y clang-18 lld-18
         sudo ./cross/setup-alternatives.sh
 
     - name: Fix sources.list (cross)
@@ -426,7 +426,7 @@ jobs:
         ARCH: ${{matrix.arch}}
         EXTRA_CMAKE_OPTIONS: -G Ninja ${{env.extra_cmake_options}} -DTOYWASM_TARBALL_SUFFIX=-${{matrix.name}}
       run: |
-        sudo ./cross/setup-focal-proposed.sh
+        sudo ./cross/setup-apt-llvm-org.sh
         sudo -E ./cross/cross-setup.sh
         sudo ./cross/setup-alternatives.sh
         ./cross/cross-cmake-configure.sh
diff --git a/cmake/ToywasmConfig.cmake b/cmake/ToywasmConfig.cmake
index 93267b00..2589fd77 100644
--- a/cmake/ToywasmConfig.cmake
+++ b/cmake/ToywasmConfig.cmake
@@ -215,10 +215,7 @@ if (CMAKE_C_COMPILER_ID MATCHES "Clang")
 # lld doesn't seem to support s390
 # ld.lld: error: unknown emulation: elf64_s390
 # https://github.com/llvm/llvm-project/blob/93b7bdcda7072581ef3f5ceaae8c4f0d549a0845/lld/ELF/Driver.cpp#L142-L166
-#
-# lld doesn't seem to support riscv relaxizations
-# ld.lld: error: /usr/bin/../lib/gcc-cross/riscv64-linux-gnu/9/../../../../riscv64-linux-gnu/lib/crt1.o:(.text+0x0): relocation R_RISCV_ALIGN requires unimplemented linker relaxation; recompile with -mno-relax
-if(NOT TRIPLET MATCHES "s390" AND NOT TRIPLET MATCHES "riscv64")
+if(NOT TRIPLET MATCHES "s390")
 set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fuse-ld=lld")
 else()
 set(USE_IPO OFF)
@@ -226,12 +223,6 @@ endif()
 endif()
 endif()
 
-# clang-13 on ubuntu/focal:
-# ld.lld: error: lto.tmp: cannot link object files with different floating-point ABI
-#if(TRIPLET MATCHES "riscv64")
-#set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,-plugin-opt=-target-abi=lp64d")
-#endif()
-
 if(TRIPLET MATCHES "i386")
 # x87 doesn't preserve sNaN as IEEE 754 and wasm expect.
 # unfortunately, clang doesn't have -mno-fp-ret-in-387.
@@ -338,6 +329,20 @@ endif()
 if(CMAKE_C_COMPILER_ID STREQUAL GNU)
 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-builtin")
 endif()
+# Clang 18's builtin ceil() etc seems to propagate sNaN as it is.
+# (ubuntu/focal, riscv64, on qemu)
+if(CMAKE_C_COMPILER_ID STREQUAL Clang)
+if(TRIPLET MATCHES "riscv64")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-builtin-floor")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-builtin-floorf")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-builtin-ceil")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-builtin-ceilf")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-builtin-trunc")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-builtin-truncf")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-builtin-rint")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-builtin-rintf")
+endif()
+endif()
 
 set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} -fomit-frame-pointer")
 #set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} -Xclang -fmerge-functions")
diff --git a/cross/README.md b/cross/README.md
index 108dacbf..7a6d6567 100644
--- a/cross/README.md
+++ b/cross/README.md
@@ -11,7 +11,7 @@ Our github CI jobs also use these scripts.
 
 Expected usage:
 ```
-./cross/setup-focal-proposed.sh
+./cross/setup-apt-llvm-org.sh
 export ARCH=arm64
 ./cross/cross-setup.sh
 ./cross/setup-alternatives.sh
diff --git a/cross/cross-setup.sh b/cross/cross-setup.sh
index f20d7bbc..a2b1092d 100755
--- a/cross/cross-setup.sh
+++ b/cross/cross-setup.sh
@@ -2,7 +2,7 @@
 
 set -e
 
-LLVM_VERSION=13
+LLVM_VERSION=18
 
 dpkg --add-architecture ${ARCH}
 apt update
diff --git a/cross/setup-alternatives.sh b/cross/setup-alternatives.sh
index 2cddea0c..835eede6 100755
--- a/cross/setup-alternatives.sh
+++ b/cross/setup-alternatives.sh
@@ -2,7 +2,7 @@
 
 set -e
 
-LLVM_VERSION=${LLVM_VERSION:-13}
+LLVM_VERSION=${LLVM_VERSION:-18}
 ALT_PRIO=100
 
 COMMANDS=${1:-clang clang++ llvm-ar llvm-ranlib ld.lld lld}
diff --git a/cross/setup-apt-llvm-org.sh b/cross/setup-apt-llvm-org.sh
new file mode 100755
index 00000000..a30fcd16
--- /dev/null
+++ b/cross/setup-apt-llvm-org.sh
@@ -0,0 +1,11 @@
+#! /bin/sh
+
+# https://apt.llvm.org/
+
+apt-get update
+apt-get install -y curl gnupg1
+curl https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -
+
+cat <<EOF > /etc/apt/sources.list.d/apt-llvm-org.list
+deb http://apt.llvm.org/focal/ llvm-toolchain-focal-18 main
+EOF
diff --git a/lib/insn.c b/lib/insn.c
index 23bbabfc..05943d1c 100644
--- a/lib/insn.c
+++ b/lib/insn.c
@@ -178,7 +178,7 @@ get_func_indirect(struct exec_context *ectx, uint32_t tableidx,
 
 /*
  * WASM float min/max follow IEEE 754-2019 minimum/maximum
- * semantics:
+ * semantics, which are different from C fmin/fmax functions:
  *
  * - If either operand is a NaN (Note: can be an sNaN), returns a qNaN.
  * - -0.0 < +0.0