qemu-arm: Merge RISC-V 32-bit support into qemu-arm port.

Currently both the qemu-arm and qemu-riscv ports share a lot of code and
functionality.  This commit merges the qemu-riscv port into the qemu-arm
port.  The only real differences between the two are the toolchains used to
build the code, and the initialisation/startup framework.  Everything else
is pretty much the same, so this brings the following benefits:
- less code duplication
- less burden on maintenance
- generalised qemu port, could in the future support other architectures

A new board `VIRT_RV32` has been added to the qemu-arm port which is the
existing RISC-V board from the qemu-riscv port.  To build it:

    $ make BOARD=VIRT_RV32 repl

To cleanly separate the code for the different architectures, startup code
has been moved to ports/qemu-arm/mcu/<arch>/.

Signed-off-by: Damien George <damien@micropython.org>

.github/workflows/ports_qemu-arm.yml

@@ -19,14 +19,26 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
-  build_and_test:
+  build_and_test_arm:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v4
     - name: Install packages
-      run: source tools/ci.sh && ci_qemu_arm_setup
+      run: source tools/ci.sh && ci_qemu_setup_arm
     - name: Build and run test suite
-      run: source tools/ci.sh && ci_qemu_arm_build
+      run: source tools/ci.sh && ci_qemu_build_arm
+    - name: Print failures
+      if: failure()
+      run: tests/run-tests.py --print-failures
+
+  build_and_test_rv32:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Install packages
+      run: source tools/ci.sh && ci_qemu_setup_rv32
+    - name: Build and run test suite
+      run: source tools/ci.sh && ci_qemu_build_rv32
     - name: Print failures
       if: failure()
       run: tests/run-tests.py --print-failures

ports/qemu-arm/Makefile

@@ -1,3 +1,6 @@
+################################################################################
+# Initial setup of Makefile environment
+
 BOARD ?= MPS2_AN385
 
 # Make the build directory reflect the board.
@@ -14,16 +17,79 @@ QSTR_DEFS = qstrdefsport.h
 
 # MicroPython feature configurations
 MICROPY_ROM_TEXT_COMPRESSION ?= 1
+
+ifeq ($(QEMU_ARCH),arm)
 FROZEN_MANIFEST ?= "freeze('test-frzmpy')"
+endif
+ifeq ($(QEMU_ARCH),riscv32)
+FROZEN_MANIFEST ?= "freeze('test-frzmpy', ('frozen_const.py', 'frozen_viper.py', 'native_frozen_align.py'))"
+endif
 
 # include py core make definitions
 include $(TOP)/py/py.mk
 include $(TOP)/extmod/extmod.mk
 
+################################################################################
+# ARM specific settings
+
+ifeq ($(QEMU_ARCH),arm)
+
 CROSS_COMPILE ?= arm-none-eabi-
 
+LDFLAGS += -nostdlib
+LIBS = $(shell $(CC) $(CFLAGS) -print-libgcc-file-name)
+
+SRC_C += \
+	mcu/arm/startup.c \
+	shared/runtime/semihosting_arm.c \
+
+endif
+
+################################################################################
+# RISC-V 32-bit specific settings
+
+ifeq ($(QEMU_ARCH),riscv32)
+
+CROSS_COMPILE ?= riscv64-unknown-elf-
+
+GCC_VERSION = $(word 1, $(subst ., , $(shell $(CC) -dumpversion)))
+
+RV32_ABI = ilp32
+
+QEMU_ARGS += -bios none
+
+# GCC 10 and lower do not recognise the Zicsr extension in the architecture name.
+ifeq ($(shell test $(GCC_VERSION) -le 10; echo $$?),0)
+RV32_ARCH ?= rv32imac
+else
+# Recent GCC versions explicitly require to declare extensions.
+RV32_ARCH ?= rv32imac_zicsr
+endif
+
+AFLAGS += -mabi=$(RV32_ABI) -march=$(RV32_ARCH)
+CFLAGS += $(AFLAGS)
+LDFLAGS += -mabi=$(RV32_ABI) -march=$(RV32_ARCH) -Wl,-EL
+
+SRC_C += \
+	mcu/rv32/interrupts.c \
+	mcu/rv32/startup.c \
+
+SRC_BOARD_O += mcu/rv32/entrypoint.o
+
+endif
+
+################################################################################
+# Project specific settings and compiler/linker flags
+
 QEMU_SYSTEM = qemu-system-$(QEMU_ARCH)
 QEMU_ARGS += -machine $(QEMU_MACHINE) -nographic -monitor null -semihosting
+QEMU_ARGS += $(QEMU_EXTRA)
+
+# Specifying QEMU_DEBUG=1 will block qemu until a debugger is connected.
+ifeq ($(QEMU_DEBUG),1)
+QEMU_DEBUG_ARGS ?= -s
+QEMU_ARGS += -S $(QEMU_DEBUG_ARGS) $(QEMU_DEBUG_EXTRA)
+endif
 
 INC += -I.
 INC += -I$(TOP)
@@ -34,6 +100,8 @@ CFLAGS += $(INC) -Wall -Wpointer-arith -Wdouble-promotion -Wfloat-conversion -We
 	 -ffunction-sections -fdata-sections
 CFLAGS += $(CFLAGS_EXTRA)
 
+LDFLAGS += -T $(LDSCRIPT) -Wl,--gc-sections -Wl,-Map=$(@:.elf=.map)
+
 # Debugging/Optimization
 ifeq ($(DEBUG), 1)
 CFLAGS += -g
@@ -42,25 +110,31 @@ else
 COPT += -Os -DNDEBUG
 endif
 
-## With CoudeSourcery it's actually a little different, you just need `-T generic-m-hosted.ld`.
-## Although for some reason `$(LD)` will not find that linker script, it works with `$(CC)`.
-## It turns out that this is specific to CoudeSourcery, and ARM version of GCC ships something
-## else instead and according to the following files, this is what we need to pass to `$(CC).
-## - gcc-arm-none-eabi-4_8-2014q1/share/gcc-arm-none-eabi/samples/src/makefile.conf
-## - gcc-arm-none-eabi-4_8-2014q1/share/gcc-arm-none-eabi/samples/src/qemu/Makefile
-LDFLAGS= -T $(LDSCRIPT) --gc-sections -Map=$(@:.elf=.map)
-LIBS = $(shell $(CC) $(CFLAGS) -print-libgcc-file-name)
+# If Picolibc is available then select it explicitly.  Ubuntu 22.04 ships its
+# bare metal RISC-V toolchain with Picolibc rather than Newlib, and the default
+# is "nosys" so a value must be provided.  To avoid having per-distro
+# workarounds, always select Picolibc if available.
+PICOLIBC_SPECS = $(shell $(CC) --print-file-name=picolibc.specs)
+ifeq ($(PICOLIBC_SPECS),picolibc.specs)
+# Picolibc was not found.
+else
+$(info picolibc used $(PICOLIBC_SPECS))
+SPECS_FRAGMENT = --specs=$(PICOLIBC_SPECS)
+CFLAGS += $(SPECS_FRAGMENT)
+LDFLAGS += $(SPECS_FRAGMENT)
+endif
 
-SRC_C = \
+################################################################################
+# Source files and libraries
+
+SRC_C += \
 	main.c \
-	startup.c \
 	uart.c \
 	mphalport.c \
 	shared/libc/string0.c \
 	shared/readline/readline.c \
 	shared/runtime/interrupt_char.c \
 	shared/runtime/pyexec.c \
-	shared/runtime/semihosting_arm.c \
 	shared/runtime/stdout_helpers.c \
 	shared/runtime/sys_stdio_mphal.c \
 
@@ -75,6 +149,9 @@ OBJ += $(addprefix $(BUILD)/, $(LIB_SRC_C:.c=.o))
 # List of sources for qstr extraction
 SRC_QSTR += $(SRC_C) $(LIB_SRC_C)
 
+################################################################################
+# Main targets
+
 all: $(BUILD)/firmware.elf
 
 .PHONY: repl
@@ -91,9 +168,11 @@ test: $(BUILD)/firmware.elf
 	$(eval DIRNAME=ports/$(notdir $(CURDIR)))
 	cd $(TOP)/tests && ./run-tests.py --target qemu-arm --device execpty:"$(QEMU_SYSTEM) $(QEMU_ARGS) -serial pty -kernel ../$(DIRNAME)/$<" $(RUN_TESTS_ARGS) $(RUN_TESTS_EXTRA)
 
-## `$(LD)` doesn't seem to like `--specs` for some reason, but we can just use `$(CC)` here.
 $(BUILD)/firmware.elf: $(LDSCRIPT) $(OBJ)
-	$(Q)$(LD) $(LDFLAGS) -o $@ $(OBJ) $(LIBS)
+	$(Q)$(CC) $(LDFLAGS) -o $@ $(OBJ) $(LIBS)
 	$(Q)$(SIZE) $@
 
+################################################################################
+# Remaining make rules
+
 include $(TOP)/py/mkrules.mk

ports/qemu-arm/README.md

@@ -1,8 +1,8 @@
 MicroPython port to qemu-arm
 ============================
 
-This is experimental, community-supported port for Cortex-M emulation as
-provided by QEMU (http://qemu.org).
+This is experimental, community-supported port for Cortex-M and RISC-V RV32IMC
+emulation as provided by QEMU (http://qemu.org).
 
 The purposes of this port are to enable:
 
@@ -18,6 +18,25 @@ The purposes of this port are to enable:
     - no need to use OpenOCD or anything else that might slow down the
       process in terms of plugging things together, pressing buttons, etc.
 
+Dependencies
+------------
+
+### ARM
+
+For ARM-based boards the build requires a bare-metal ARM toolchain, such as
+`arm-none-eabi-gcc`.
+
+### RISC-V
+
+For RISC-V-based boards the build requires a bare metal RISC-V toolchain with GCC 10
+or later, either with multilib support or 32 bits specific (M, C, and Zicsr
+extensions must be supported, along with ilp32 ABI).  Both newlib and picolibc are
+supported, with the latter having precedence if found.
+
+Most pre-built toolchains should work out of the box, either coming from your
+Linux distribution's package manager, or independently packaged ones like
+[xPack](https://xpack.github.io/dev-tools/riscv-none-elf-gcc/).
+
 Build instructions
 ------------------
 
@@ -36,12 +55,13 @@ different board pass the `BOARD` argument to `make`, for example:
 
 Available boards are:
 
-| Name for `BOARD=` | Corresponding qemu board |
-| ----------------- | ------------------------ |
-| `MICROBIT`        | `microbit`               |
-| `MPS2_AN385`      | `mps2-an385`             |
-| `NETDUINO2`       | `netduino2`              |
-| `SABRELITE`       | `sabrelite`              |
+| Name for `BOARD=` | Architecture | Corresponding qemu board |
+| ----------------- | ------------ | ------------------------ |
+| `MICROBIT`        | `arm`        | `microbit`               |
+| `MPS2_AN385`      | `arm`        | `mps2-an385`             |
+| `NETDUINO2`       | `arm`        | `netduino2`              |
+| `SABRELITE`       | `arm`        | `sabrelite`              |
+| `VIRT_RV32`       | `riscv32`    | `virt`                   |
 
 Running
 -------
@@ -84,3 +104,9 @@ The following options can be specified on the `make` command line:
 - `CFLAGS_EXTRA`: pass in extra flags for the compiler.
 - `RUN_TESTS_EXTRA`: pass in extra flags for `run-tests.py` when invoked via
   `make test`.
+- `QEMU_DEBUG=1`: when running qemu (via `repl`, `run` or `test` target), qemu
+  will block until a debugger is connected.  By default it waits for a gdb connection
+  on TCP port 1234.
+- `QEMU_DEBUG_ARGS`: defaults to `-s` (gdb on TCP port 1234), but can be overridden
+  with different qemu gdb arguments.
+- `QEMU_DEBUG_EXTRA`: extra options to pass to qemu when `QEMU_DEBUG=1` is used.

ports/qemu-arm/boards/MICROBIT.mk

@@ -6,7 +6,7 @@ CFLAGS += -mthumb -mcpu=cortex-m0 -mfloat-abi=soft
 CFLAGS += -DQEMU_SOC_NRF51
 CFLAGS += -DMICROPY_HW_MCU_NAME='"nRF51"'
 
-LDSCRIPT = nrf51.ld
+LDSCRIPT = mcu/arm/nrf51.ld
 
 SRC_BOARD_O = shared/runtime/gchelper_native.o shared/runtime/gchelper_thumb1.o
 

ports/qemu-arm/boards/MPS2_AN385.mk

@@ -5,7 +5,7 @@ CFLAGS += -mthumb -mcpu=cortex-m3 -mfloat-abi=soft
 CFLAGS += -DQEMU_SOC_MPS2
 CFLAGS += -DMICROPY_HW_MCU_NAME='"Cortex-M3"'
 
-LDSCRIPT = mps2.ld
+LDSCRIPT = mcu/arm/mps2.ld
 
 SRC_BOARD_O = shared/runtime/gchelper_native.o shared/runtime/gchelper_thumb2.o
 

ports/qemu-arm/boards/NETDUINO2.mk

@@ -5,7 +5,7 @@ CFLAGS += -mthumb -mcpu=cortex-m3 -mfloat-abi=soft
 CFLAGS += -DQEMU_SOC_STM32
 CFLAGS += -DMICROPY_HW_MCU_NAME='"STM32"'
 
-LDSCRIPT = stm32.ld
+LDSCRIPT = mcu/arm/stm32.ld
 
 SRC_BOARD_O = shared/runtime/gchelper_native.o shared/runtime/gchelper_thumb2.o
 

ports/qemu-arm/boards/SABRELITE.mk

@@ -8,7 +8,7 @@ CFLAGS += -DMICROPY_HW_MCU_NAME='"Cortex-A9"'
 # Cortex-A9 should support unaligned-access, but qemu doesn't seem to.
 CFLAGS += -mno-unaligned-access
 
-LDSCRIPT = imx6.ld
+LDSCRIPT = mcu/arm/imx6.ld
 
 SRC_BOARD_O = shared/runtime/gchelper_generic.o
 

ports/qemu-arm/boards/VIRT_RV32.mk

@@ -0,0 +1,14 @@
+QEMU_ARCH = riscv32
+QEMU_MACHINE = virt
+
+CFLAGS += -DQEMU_SOC_VIRT
+CFLAGS += -DMICROPY_HW_MCU_NAME='"$(RV32_ARCH)"'
+
+LDSCRIPT = mcu/rv32/virt.ld
+
+SRC_BOARD_O += shared/runtime/gchelper_native.o shared/runtime/gchelper_rv32i.o
+
+MPY_CROSS_FLAGS += -march=rv32imc
+
+# These Thumb tests don't run on RV32, so exclude them.
+RUN_TESTS_ARGS = --exclude 'inlineasm|qemu-arm/asm_test'

ports/qemu-arm/mpconfigport.h

@@ -37,6 +37,8 @@
 #define MICROPY_EMIT_THUMB          (1)
 #define MICROPY_EMIT_INLINE_THUMB   (1)
 #define MICROPY_MAKE_POINTER_CALLABLE(p) ((void *)((mp_uint_t)(p) | 1))
+#elif defined(__riscv)
+#define MICROPY_EMIT_RV32           (1)
 #endif
 
 #define MICROPY_MALLOC_USES_ALLOCATED_SIZE (1)
@@ -47,7 +49,11 @@
 #define MICROPY_FLOAT_IMPL          (MICROPY_FLOAT_IMPL_FLOAT)
 #define MICROPY_WARNINGS            (1)
 #define MICROPY_PY_IO_IOBASE        (0)
+#if defined(__ARM_ARCH)
 #define MICROPY_PY_SYS_PLATFORM     "qemu-arm"
+#elif defined(__riscv)
+#define MICROPY_PY_SYS_PLATFORM     "qemu-riscv32"
+#endif
 #define MICROPY_PY_SYS_STDIO_BUFFER (0)
 #define MICROPY_PY_SELECT           (0)
 #define MICROPY_PY_TIME             (0)

ports/qemu-arm/mphalport.h

@@ -24,4 +24,5 @@
  * THE SOFTWARE.
  */
 
+#include <stddef.h>
 #include "shared/runtime/interrupt_char.h"