cmake: rename rv32 toolchain file to riscv32-unknown-elf-rv32imc.cmake (#537)

Renamed cmake/riscv64-gcc-rv32imc.cmake to the accurate name
cmake/riscv32-unknown-elf-rv32imc.cmake and switch the compiler
from riscv64-unknown-elf-gcc to riscv32-unknown-elf-gcc.

The riscv-collab riscv64-elf toolchain has no rv32 multilib and
will fail to link soft-float and integer helpers (__clzsi2, __muldf3,
etc.) when building for -march=rv32imc_zicsr -mabi=ilp32.  The
dedicated riscv32-unknown-elf-gcc (riscv-collab riscv32-elf release,
installed to /opt/riscv by scripts/install_riscv.sh) ships the correct
native rv32/ilp32 libgcc — analogous to arm-none-eabi-gcc for Cortex-M.

The old filename is kept as a two-line compatibility alias that includes
the new file, so any out-of-tree users who hardcode the old path still work.

Also update:
- core_v_mcu/build.sh: reference new cmake filename
- core_v_mcu/README.md: update prerequisites table and toolchain docs

Co-authored-by: Copilot <[email protected]>

4 files changed, 87 insertions, 89 deletions

diff --git a/cmake/riscv32-unknown-elf-rv32imc.cmake b/cmake/riscv32-unknown-elf-rv32imc.cmake
new file mode 100644
index 00000000..7e935689
--- /dev/null
+++ b/cmake/riscv32-unknown-elf-rv32imc.cmake
@@ -0,0 +1,69 @@
+# /***************************************************************************
+#  * Copyright (C) 2026 Eclipse ThreadX contributors
+#  *
+#  * This program and the accompanying materials are made available under the
+#  * terms of the MIT License which is available at
+#  * https://opensource.org/licenses/MIT.
+#  *
+#  * SPDX-License-Identifier: MIT
+#  ***************************************************************************/
+
+# CMake toolchain file for CORE-V MCU (CV32E40P, RV32IMC)
+#
+# Uses the dedicated riscv32-unknown-elf-gcc bare-metal toolchain from
+# riscv-collab (riscv32-elf-ubuntu-24.04-gcc.tar.xz, installs to /opt/riscv).
+# This is the correct toolchain for RV32 bare-metal targets — analogous to
+# arm-none-eabi-gcc for Cortex-M.  It ships a native rv32/ilp32 libgcc with
+# all soft-float and integer helpers (__clzsi2, __muldf3, etc.) built for the
+# correct ABI.
+#
+# Do NOT use riscv64-unknown-elf-gcc for this target: the riscv-collab
+# riscv64-elf toolchain is built without rv32 multilib and will produce
+# missing-symbol linker errors with -nodefaultlibs.
+#
+# Install both toolchains with:  bash scripts/install_riscv.sh
+#
+# Target ISA : rv32imc_zicsr  (integer, multiply, compressed, Zicsr)
+# ABI        : ilp32           (32-bit int/long/ptr, no hardware FP)
+# Code model : medlow          (addresses in [0, 2 GiB))
+
+set(CMAKE_SYSTEM_NAME Generic)
+set(CMAKE_SYSTEM_PROCESSOR riscv)
+
+set(THREADX_ARCH "risc-v32")
+set(THREADX_TOOLCHAIN "gnu")
+
+set(ARCH_FLAGS "-march=rv32imc_zicsr -mabi=ilp32 -mcmodel=medlow")
+set(CFLAGS   "${ARCH_FLAGS}")
+set(ASFLAGS  "${ARCH_FLAGS}")
+set(LDFLAGS  "${ARCH_FLAGS}")
+
+# Dedicated riscv32 bare-metal toolchain (riscv-collab riscv32-elf release).
+set(CMAKE_C_COMPILER    riscv32-unknown-elf-gcc)
+set(CMAKE_CXX_COMPILER  riscv32-unknown-elf-g++)
+set(AS                  riscv32-unknown-elf-as)
+set(AR                  riscv32-unknown-elf-ar)
+set(OBJCOPY             riscv32-unknown-elf-objcopy)
+set(OBJDUMP             riscv32-unknown-elf-objdump)
+set(SIZE                riscv32-unknown-elf-size)
+
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
+
+# Use static library for compiler feature probing (no linker script yet)
+set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+
+set(CMAKE_C_FLAGS   "${CFLAGS}"  CACHE INTERNAL "c compiler flags")
+set(CMAKE_CXX_FLAGS "${CFLAGS}"  CACHE INTERNAL "cxx compiler flags")
+set(CMAKE_ASM_FLAGS "${ASFLAGS} -D__ASSEMBLER__" CACHE INTERNAL "asm compiler flags")
+set(CMAKE_EXE_LINKER_FLAGS "${LDFLAGS}" CACHE INTERNAL "exe link flags")
+
+set(CMAKE_C_FLAGS_DEBUG   "-Og -g -ggdb3" CACHE INTERNAL "c debug flags")
+set(CMAKE_CXX_FLAGS_DEBUG "-Og -g -ggdb3" CACHE INTERNAL "cxx debug flags")
+set(CMAKE_ASM_FLAGS_DEBUG "-g -ggdb3"     CACHE INTERNAL "asm debug flags")
+
+set(CMAKE_C_FLAGS_RELEASE   "-Os" CACHE INTERNAL "c release flags")
+set(CMAKE_CXX_FLAGS_RELEASE "-Os" CACHE INTERNAL "cxx release flags")
+set(CMAKE_ASM_FLAGS_RELEASE ""    CACHE INTERNAL "asm release flags")
diff --git a/cmake/riscv64-gcc-rv32imc.cmake b/cmake/riscv64-gcc-rv32imc.cmake
index aa19b624..d3d50115 100644
--- a/cmake/riscv64-gcc-rv32imc.cmake
+++ b/cmake/riscv64-gcc-rv32imc.cmake
@@ -1,76 +1,2 @@
-# /***************************************************************************
-#  * Copyright (C) 2026 Eclipse ThreadX contributors
-#  *
-#  * This program and the accompanying materials are made available under the
-#  * terms of the MIT License which is available at
-#  * https://opensource.org/licenses/MIT.
-#  *
-#  * AI Disclosure: This file was largely AI-generated by Copilot (Sonnet 4.6).
-#  * The AI-generated portions may be considered public domain (CC0-1.0)
-#  * and not subject to the project's licence. The human contributor has
-#  * reviewed and verified that the code is correct.
-#  *
-#  * SPDX-License-Identifier: MIT and CC0-1.0
-#  ***************************************************************************/
-
-# CMake toolchain file for CORE-V MCU (CV32E40P, RV32IMC)
-#
-# Uses the riscv64-unknown-elf-gcc cross-compiler to produce rv32imc/ilp32
-# bare-metal firmware.  The riscv-collab toolchain (installed to /opt/riscv by
-# scripts/install_riscv.sh) is used by default.  The Ubuntu package
-# gcc-riscv64-unknown-elf also works and can be installed via install_deps.sh.
-#
-# Note: the riscv-collab toolchain is built without multilib, so it does not
-# ship an rv32/ilp32 libgcc.  The CORE-V MCU BSP provides a weak __clzsi2
-# fallback in bsp/clz.c to satisfy any __builtin_clz() calls without relying
-# on libgcc.
-#
-# Target ISA : rv32imc_zicsr  (integer, multiply, compressed, Zicsr)
-# ABI        : ilp32           (32-bit int/long/ptr, no hardware FP)
-# Code model : medlow          (addresses in [0, 2 GiB))
-
-set(CMAKE_SYSTEM_NAME Generic)
-set(CMAKE_SYSTEM_PROCESSOR riscv)
-
-set(THREADX_ARCH "risc-v32")
-set(THREADX_TOOLCHAIN "gnu")
-
-set(ARCH_FLAGS "-march=rv32imc_zicsr -mabi=ilp32 -mcmodel=medlow")
-set(CFLAGS   "${ARCH_FLAGS}")
-set(ASFLAGS  "${ARCH_FLAGS}")
-set(LDFLAGS  "${ARCH_FLAGS}")
-
-# Toolchain binaries: riscv64-unknown-elf-gcc cross-compiler.
-# The riscv-collab toolchain (scripts/install_riscv.sh → /opt/riscv/bin) is the
-# preferred choice.  The Ubuntu package (gcc-riscv64-unknown-elf, install via
-# install_deps.sh) is also supported.  Both are searched via PATH so whichever
-# comes first is used; ensure /opt/riscv/bin precedes /usr/bin if you want the
-# riscv-collab toolchain.
-set(CMAKE_C_COMPILER    riscv64-unknown-elf-gcc)
-set(CMAKE_CXX_COMPILER  riscv64-unknown-elf-g++)
-set(AS                  riscv64-unknown-elf-as)
-set(AR                  riscv64-unknown-elf-ar)
-set(OBJCOPY             riscv64-unknown-elf-objcopy)
-set(OBJDUMP             riscv64-unknown-elf-objdump)
-set(SIZE                riscv64-unknown-elf-size)
-
-set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
-set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
-set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
-set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
-
-# Use static library for compiler feature probing (no linker script yet)
-set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
-
-set(CMAKE_C_FLAGS   "${CFLAGS}"  CACHE INTERNAL "c compiler flags")
-set(CMAKE_CXX_FLAGS "${CFLAGS}"  CACHE INTERNAL "cxx compiler flags")
-set(CMAKE_ASM_FLAGS "${ASFLAGS} -D__ASSEMBLER__" CACHE INTERNAL "asm compiler flags")
-set(CMAKE_EXE_LINKER_FLAGS "${LDFLAGS}" CACHE INTERNAL "exe link flags")
-
-set(CMAKE_C_FLAGS_DEBUG   "-Og -g -ggdb3" CACHE INTERNAL "c debug flags")
-set(CMAKE_CXX_FLAGS_DEBUG "-Og -g -ggdb3" CACHE INTERNAL "cxx debug flags")
-set(CMAKE_ASM_FLAGS_DEBUG "-g -ggdb3"     CACHE INTERNAL "asm debug flags")
-
-set(CMAKE_C_FLAGS_RELEASE   "-Os" CACHE INTERNAL "c release flags")
-set(CMAKE_CXX_FLAGS_RELEASE "-Os" CACHE INTERNAL "cxx release flags")
-set(CMAKE_ASM_FLAGS_RELEASE ""    CACHE INTERNAL "asm release flags")
+# This file is a compatibility alias.  Use riscv32-unknown-elf-rv32imc.cmake.
+include(${CMAKE_CURRENT_LIST_DIR}/riscv32-unknown-elf-rv32imc.cmake)
diff --git a/ports/risc-v32/gnu/example_build/core_v_mcu/README.md b/ports/risc-v32/gnu/example_build/core_v_mcu/README.md
index d94759d0..d2b8a844 100644
--- a/ports/risc-v32/gnu/example_build/core_v_mcu/README.md
+++ b/ports/risc-v32/gnu/example_build/core_v_mcu/README.md
@@ -57,15 +57,18 @@ Or install individually:
 
 | Tool | Minimum version | Notes |
 |------|----------------|-------|
-| `riscv64-unknown-elf-gcc` | 13.x | `apt install gcc-riscv64-unknown-elf binutils-riscv64-unknown-elf` |
+| `riscv32-unknown-elf-gcc` | 15.x | riscv-collab `riscv32-elf` release — run `bash scripts/install_riscv.sh` |
 | CMake | 3.15 | `apt install cmake` |
 | Ninja | 1.10 | `apt install ninja-build` |
 | OpenOCD | 0.12 | `apt install openocd` |
-| GDB | any multiarch | `apt install gdb-multiarch` — Ubuntu does not ship `riscv64-unknown-elf-gdb` |
+| GDB | any multiarch | `apt install gdb-multiarch` — Ubuntu does not ship `riscv32-unknown-elf-gdb` |
 
-> **Note:** There is no `riscv32-unknown-elf-gcc` package required.  The
-> `riscv64-unknown-elf-gcc` compiler generates RV32 code when passed
-> `-march=rv32imc_zicsr -mabi=ilp32`, as configured by the toolchain file.
+> **Note:** Use the dedicated `riscv32-unknown-elf-gcc` bare-metal toolchain
+> (riscv-collab `riscv32-elf` release, installs to `/opt/riscv`).  This is
+> the RV32 equivalent of `arm-none-eabi-gcc` and ships a native rv32/ilp32
+> libgcc with all required soft-float and integer helpers.  Do **not** use
+> `riscv64-unknown-elf-gcc` — the riscv-collab riscv64-elf toolchain has no
+> rv32 multilib and will produce missing-symbol linker errors.
 
 ---
 
@@ -221,19 +224,19 @@ build/demo_threadx.map   — linker map
 ```bash
 THREADX_ROOT=$(realpath ../../../../..)
 cmake -B build -G Ninja \
-      -DCMAKE_TOOLCHAIN_FILE="${THREADX_ROOT}/cmake/riscv64-gcc-rv32imc.cmake" \
+      -DCMAKE_TOOLCHAIN_FILE="${THREADX_ROOT}/cmake/riscv32-unknown-elf-rv32imc.cmake" \
       .
 cmake --build build
 ```
 
 ### Toolchain file
 
-`${THREADX_ROOT}/cmake/riscv64-gcc-rv32imc.cmake` sets:
+`${THREADX_ROOT}/cmake/riscv32-unknown-elf-rv32imc.cmake` sets:
 
 ```
-CMAKE_C_COMPILER    riscv64-unknown-elf-gcc
-CMAKE_ASM_COMPILER  riscv64-unknown-elf-gcc
-CMAKE_OBJCOPY       riscv64-unknown-elf-objcopy
+CMAKE_C_COMPILER    riscv32-unknown-elf-gcc
+CMAKE_ASM_COMPILER  riscv32-unknown-elf-gcc
+CMAKE_OBJCOPY       riscv32-unknown-elf-objcopy
 CMAKE_C_FLAGS       -march=rv32imc_zicsr -mabi=ilp32 -mcmodel=medlow
 ```
 
@@ -285,7 +288,7 @@ port 3333 (GDB) and 4444 (telnet).
 In a second terminal:
 
 ```bash
-riscv64-unknown-elf-gdb --command=gdb_init
+riscv32-unknown-elf-gdb --command=gdb_init
 ```
 
 `gdb_init` connects to OpenOCD, loads the ELF, sets a breakpoint at `main`, and
@@ -485,7 +488,7 @@ bash deploy.sh --debug
 ```
 
 The script starts OpenOCD in the background, waits for it to become ready,
-then drives `riscv64-unknown-elf-gdb` to load the ELF.  OpenOCD is always
+then drives `riscv32-unknown-elf-gdb` to load the ELF.  OpenOCD is always
 stopped on exit (including Ctrl-C).
 
 ---
diff --git a/ports/risc-v32/gnu/example_build/core_v_mcu/build.sh b/ports/risc-v32/gnu/example_build/core_v_mcu/build.sh
index fe78a8e6..c2ccfc55 100755
--- a/ports/risc-v32/gnu/example_build/core_v_mcu/build.sh
+++ b/ports/risc-v32/gnu/example_build/core_v_mcu/build.sh
@@ -4,6 +4,6 @@ SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
 THREADX_ROOT="${SCRIPT_DIR}/../../../../.."
 cmake -B "${SCRIPT_DIR}/build" \
       -G Ninja \
-      -DCMAKE_TOOLCHAIN_FILE="${THREADX_ROOT}/cmake/riscv64-gcc-rv32imc.cmake" \
+      -DCMAKE_TOOLCHAIN_FILE="${THREADX_ROOT}/cmake/riscv32-unknown-elf-rv32imc.cmake" \
       "${SCRIPT_DIR}"
 cmake --build "${SCRIPT_DIR}/build"