MicroPython: Removed Newlib dependency from headless builds. Streamline build process for readability.

Author: ccattuto

advanced/micropython/README.md

@@ -15,12 +15,12 @@ git submodule update --init lib/micropython-lib
 
 The port supports three build modes:
 
-### 1. REPL_SYSCALL (default)
+### 1. REPL_NEWLIB (default)
 Interactive REPL on host's stdio:
 ```bash
 make
 # or explicitly
-make MODE=REPL_SYSCALL
+make MODE=REPL_NEWLIB
 ```
 
 ### 2. HEADLESS
@@ -29,28 +29,40 @@ Executes a frozen Python script with no stdio (requires `FROZEN_SCRIPT`, default
 make MODE=HEADLESS FROZEN_SCRIPT=startup.py
 ```
 
-### 3. UART
+### 3. REPL_UART
 REPL over emulated UART, with an optional frozen initialization script (requires `FROZEN_SCRIPT`, defaults to `startup.py`):
 ```bash
-make MODE=UART FROZEN_SCRIPT=startup.py
+make MODE=REPL_UART FROZEN_SCRIPT=startup.py
 ```
 
 ## Build Options
 
-- `MODE` - Build mode: `REPL_SYSCALL` (default), `HEADLESS`, or `UART`
-- `FROZEN_SCRIPT` - Python script to freeze into firmware (required for HEADLESS, optional for UART, defaults to `startup.py`)
+- `MODE` - Build mode: `REPL_NEWLIB` (default), `HEADLESS`, or `REPL_UART`
+- `FROZEN_SCRIPT` - Python script to freeze into firmware (required for HEADLESS, optional for REPL_UART, defaults to `startup.py`)
 - `RVM=1` - Enable RISC-V M extension (multiply/divide, default: enabled)
 - `RVA=0` - Enable RISC-V A extension (atomics, default: disabled)
 - `RVC=0` - Enable RISC-V C extension (compressed instructions, default: disabled)
 
+## Build Characteristics
+
+| Mode | Binary Size | Newlib | Float Support | Long Int Support |
+|------|-------------|--------|---------------|------------------|
+| REPL_NEWLIB | ~246 KB | Yes | Yes | Yes |
+| HEADLESS | ~194 KB | No | No | No |
+| REPL_UART | ~194 KB | No | No | No |
+
+**HEADLESS and REPL_UART modes** are minimal builds with no Newlib dependencies (only libgcc). They use integer-only arithmetic and have no syscall overhead, resulting in smaller binaries.
+
+**REPL_NEWLIB mode** uses full Newlib for syscall-based I/O and supports floating-point operations.
+
 ## Running
 
 In the emulator's root directory. Prebuilt binary:
 ```bash
 ./riscv-emu.py --raw-tty --ram-size=4096 prebuilt/micropython.elf 
 ```
 
-Compiled binary, REPL over stdio (REPL_SYSCALL default build mode):
+Compiled binary, REPL over stdio (REPL_NEWLIB default build mode):
 ```bash
 ./riscv-emu.py --raw-tty --ram-size=4096 advanced/micropython/port-riscv-emu.py/build/firmware.elf
 ```
@@ -60,7 +72,7 @@ Compiled binary, headless (HEADLESS build mode):
 ./riscv-emu.py ---ram-size=4096 advanced/micropython/port-riscv-emu.py/build/firmware.elf
 ```
 
-Compiled binary, REPL over UART (UART build mode):
+Compiled binary, REPL over UART (REPL_UART build mode):
 ```bash
 ./riscv-emu.py ---ram-size=4096 --uart advanced/micropython/port-riscv-emu.py/build/firmware.elf
 ```

advanced/micropython/port-riscv-emu.py/Makefile

@@ -8,20 +8,20 @@ QSTR_DEFS = qstrdefsport.h
 # MicroPython feature configurations
 MICROPY_ROM_TEXT_COMPRESSION ?= 1
 
-# Mode selection (default to REPL_SYSCALL for backwards compatibility)
-# Valid values: REPL_SYSCALL, HEADLESS, UART
-MODE ?= REPL_SYSCALL
+# Mode selection (default to REPL_NEWLIB for backwards compatibility)
+# Valid values: REPL_NEWLIB, HEADLESS, REPL_UART
+MODE ?= REPL_NEWLIB
 
-# Frozen module support for HEADLESS and UART modes
+# Frozen module support for HEADLESS and REPL_UART modes
 # The frozen script is always named startup.py
 ifeq ($(MODE),HEADLESS)
     FROZEN_ENABLED = 1
-else ifeq ($(MODE),UART)
+else ifeq ($(MODE),REPL_UART)
     FROZEN_ENABLED = 1
-else ifeq ($(MODE),REPL_SYSCALL)
+else ifeq ($(MODE),REPL_NEWLIB)
     FROZEN_ENABLED = 0
 else
-    $(error Invalid MODE=$(MODE). Valid values: REPL_SYSCALL, HEADLESS, UART)
+    $(error Invalid MODE=$(MODE). Valid values: REPL_NEWLIB, HEADLESS, REPL_UART)
 endif
 
 ifeq ($(FROZEN_ENABLED),1)
@@ -45,7 +45,12 @@ MPY_CROSS ?= $(TOP)/mpy-cross/build/mpy-cross
 MPY_TOOL ?= $(PYTHON) $(TOP)/tools/mpy-tool.py
 # Flags for mpy-cross and mpy-tool to match port configuration
 MPY_CROSS_FLAGS += -msmall-int-bits=31
-MPY_TOOL_FLAGS += -mlongint-impl=longlong
+ifeq ($(MODE),REPL_NEWLIB)
+    MPY_TOOL_FLAGS += -mlongint-impl=longlong
+else
+    # HEADLESS and REPL_UART use minimal integer implementation
+    MPY_TOOL_FLAGS += -mlongint-impl=none
+endif
 
 # Extension options - set to 1 to enable, 0 to disable
 # Note: the toolchain might not support all combinations
@@ -65,17 +70,45 @@ INC += -I$(BUILD)
 ifeq ($(CROSS), 1)
 DFU = $(TOP)/tools/dfu.py
 PYDFU = $(TOP)/tools/pydfu.py
-CFLAGS_RISCV  = -march=$(MARCH) -mabi=ilp32 -D_REENT_SMALL
+
+# Base RISC-V flags (bare-metal)
+CFLAGS_RISCV = -march=$(MARCH) -mabi=ilp32
+
+# Define MODE constants for use in C and assembly
+CFLAGS_RISCV += -DMODE_REPL_NEWLIB=1 -DMODE_HEADLESS=2 -DMODE_REPL_UART=3
+
+# Add Newlib-specific flags for REPL_NEWLIB mode
+ifeq ($(MODE),REPL_NEWLIB)
+    CFLAGS_RISCV += -D_REENT_SMALL
+endif
+
 CFLAGS += $(INC) -Wall -Werror -std=c99 $(CFLAGS_RISCV) $(COPT) -DMICROPY_PORT_MODE=MODE_$(MODE)
-LDFLAGS += -nostartfiles -static -Tlinker_newlib.ld --specs=nosys.specs
+
+# Linker flags
+LDFLAGS += -nostartfiles -static -Tmicropython.ld
+ifeq ($(MODE),REPL_NEWLIB)
+    LDFLAGS += --specs=nosys.specs
+else
+    LDFLAGS += -nostdlib
+endif
 else
 UNAME_S := $(shell uname -s)
 LD = $(CC)
 CFLAGS += $(INC) -Wall -Werror -Wdouble-promotion -Wfloat-conversion -std=c99 $(COPT) -DMICROPY_PORT_MODE=MODE_$(MODE)
 ifeq ($(UNAME_S),Linux)
-LDFLAGS += -nostartfiles -Wl,--gc-sections -static -Tlinker_newlib.ld --specs=nano.specs -Wl,-map,$@.map -Wl,-dead_strip
+LDFLAGS += -nostartfiles -Wl,--gc-sections -static -Tmicropython.ld -Wl,-map,$@.map -Wl,-dead_strip
+ifeq ($(MODE),REPL_NEWLIB)
+    LDFLAGS += --specs=nano.specs
+else
+    LDFLAGS += -nostdlib
+endif
 else ifeq ($(UNAME_S),Darwin)
-LDFLAGS += -nostartfiles -Wl,--gc-sections -static -Tlinker_newlib.ld --specs=nano.specs -Wl,-map,$@.map -Wl,-dead_strip
+LDFLAGS += -nostartfiles -Wl,--gc-sections -static -Tmicropython.ld -Wl,-map,$@.map -Wl,-dead_strip
+ifeq ($(MODE),REPL_NEWLIB)
+    LDFLAGS += --specs=nano.specs
+else
+    LDFLAGS += -nostdlib
+endif
 endif
 endif
 
@@ -99,7 +132,14 @@ endif
 # Flags for optional C++ source code
 CXXFLAGS += $(filter-out -std=c99,$(CFLAGS))
 
-LIBS = -lm
+# Libraries based on mode
+ifeq ($(MODE),REPL_NEWLIB)
+    # REPL_NEWLIB: Full Newlib with float support
+    LIBS = -lm
+else
+    # HEADLESS and REPL_UART: Minimal config (no floats, no long ints) - only libgcc
+    LIBS = -lgcc
+endif
 
 # Common source files for all build modes
 SRC_C = \
@@ -115,19 +155,24 @@ SRC_C = \
 	extmod/machine_mem.c \
 	extmod/moductypes.c
 
+# Base assembly files (bare-metal)
 SRC_S = \
-	start_newlib.S \
-    syscalls_newlib.S \
+	start.S \
 	gchelper_rv32i.S
 
+# Add syscall stubs for REPL_NEWLIB mode
+ifeq ($(MODE),REPL_NEWLIB)
+    SRC_S += syscalls_newlib.S
+endif
+
 # Select HAL based on build mode
-ifeq ($(MODE),REPL_SYSCALL)
+ifeq ($(MODE),REPL_NEWLIB)
     # Mode 1: syscall-based I/O
     SRC_C += mphalport.c
 else ifeq ($(MODE),HEADLESS)
     # Mode 2: headless (no stdio)
     SRC_C += mphalport_headless.c
-else ifeq ($(MODE),UART)
+else ifeq ($(MODE),REPL_UART)
     # Mode 3: UART MMIO I/O
     SRC_C += mphalport_uart.c
 endif

advanced/micropython/port-riscv-emu.py/main.c

@@ -20,8 +20,8 @@ int main(int argc, char *argv[]) {
 		mp_obj_list_append(mp_sys_argv, mp_obj_new_str(argv[i], strlen(argv[i])));
     }
 
-#if (MICROPY_PORT_MODE == MODE_REPL_SYSCALL)
-    // Welcome message for syscall REPL mode
+#if (MICROPY_PORT_MODE == MODE_REPL_NEWLIB)
+    // Welcome message for REPL with Newlib mode
     mp_printf(&mp_plat_print, "Welcome to MicroPython on RISC-V!\n");
 #endif
 
@@ -30,8 +30,8 @@ int main(int argc, char *argv[]) {
     pyexec_frozen_module(FROZEN_MODULE_NAME, false);
 #endif
 
-#if (MICROPY_PORT_MODE == MODE_REPL_SYSCALL) || \
-    (MICROPY_PORT_MODE == MODE_UART)
+#if (MICROPY_PORT_MODE == MODE_REPL_NEWLIB) || \
+    (MICROPY_PORT_MODE == MODE_REPL_UART)
     // Start REPL
 	pyexec_friendly_repl();
 #endif

…ython/port-riscv-emu.py/linker_newlib.ld …opython/port-riscv-emu.py/micropython.ldadvanced/micropython/port-riscv-emu.py/linker_newlib.ld renamed to advanced/micropython/port-riscv-emu.py/micropython.ld advanced/micropython/port-riscv-emu.py/linker_newlib.ld renamed to advanced/micropython/port-riscv-emu.py/micropython.ld

@@ -1,15 +1,31 @@
-#include <stdio.h>
 #include "py/obj.h"
 #include "py/lexer.h"
 #include "py/stream.h"
 #include "py/runtime.h"
 #include "py/builtin.h"
 #include "py/mpprint.h"
+#include "py/mphal.h"
+#include "mpconfigport.h"
+#include <string.h>
+
+#if (MICROPY_PORT_MODE == MODE_REPL_NEWLIB)
+    #include <stdio.h>
+    #define FATAL_ERROR(msg) do { printf("FATAL: %s\n", msg); while(1); } while(0)
+#else
+    // Bare-metal: no stdio.h (HEADLESS and REPL_UART modes)
+    static void fatal_error(const char *msg) __attribute__((noreturn));
+    static void fatal_error(const char *msg) {
+        mp_hal_stdout_tx_strn("FATAL: ", 7);
+        mp_hal_stdout_tx_strn(msg, strlen(msg));
+        mp_hal_stdout_tx_strn("\n", 1);
+        while (1);
+    }
+    #define FATAL_ERROR(msg) fatal_error(msg)
+#endif
 
 // Stub: If nlr fails, just halt.
 void nlr_jump_fail(void *val) {
-    printf("FATAL: nlr_jump_fail\n");
-    while (1);
+    FATAL_ERROR("nlr_jump_fail");
 }
 
 // Stub: We have no filesystem
@@ -19,7 +35,7 @@ mp_import_stat_t mp_import_stat(const char *path) {
 
 // Stub: no file-based imports
 mp_lexer_t *mp_lexer_new_from_file(qstr filename) {
-    printf("FATAL: mp_lexer_new_from_file() not supported\n");
+    FATAL_ERROR("mp_lexer_new_from_file() not supported");
     return NULL;
 }
 

advanced/micropython/port-riscv-emu.py/minimal_stubs.c

@@ -7,22 +7,29 @@
 // options to control how MicroPython is built
 
 // Mode definitions (set via Makefile)
-#define MODE_REPL_SYSCALL    1  // Interactive REPL with syscalls
+#define MODE_REPL_NEWLIB     1  // Interactive REPL with Newlib syscalls
 #define MODE_HEADLESS        2  // Frozen script execution, no stdio
-#define MODE_UART            3  // Frozen init script + UART REPL
+#define MODE_REPL_UART       3  // Frozen init script + UART REPL
 
 #ifndef MICROPY_PORT_MODE
-#define MICROPY_PORT_MODE MODE_REPL_SYSCALL
+#define MICROPY_PORT_MODE MODE_REPL_NEWLIB
 #endif
 
 // Use CORE_FEATURES ROM level as base, then explicitly enable what we need
 #define MICROPY_CONFIG_ROM_LEVEL (MICROPY_CONFIG_ROM_LEVEL_CORE_FEATURES)
 
-// Float support enabled for all modes
-#define MICROPY_PY_BUILTINS_FLOAT         (1)
-#define MICROPY_FLOAT_IMPL                (MICROPY_FLOAT_IMPL_FLOAT)
-#define MICROPY_PY_MATH                   (1)
-#define MICROPY_PY_CMATH                  (0)
+// Float support - disabled for HEADLESS and REPL_UART to eliminate libc dependencies
+#if (MICROPY_PORT_MODE == MODE_REPL_NEWLIB)
+    #define MICROPY_PY_BUILTINS_FLOAT     (1)
+    #define MICROPY_FLOAT_IMPL            (MICROPY_FLOAT_IMPL_FLOAT)
+    #define MICROPY_PY_MATH               (1)
+    #define MICROPY_PY_CMATH              (0)
+#else
+    #define MICROPY_PY_BUILTINS_FLOAT     (0)
+    #define MICROPY_FLOAT_IMPL            (MICROPY_FLOAT_IMPL_NONE)
+    #define MICROPY_PY_MATH               (0)
+    #define MICROPY_PY_CMATH              (0)
+#endif
 
 #define MICROPY_ENABLE_COMPILER     (1)
 #define MICROPY_ENAVLE_REPL	        (1)
@@ -36,6 +43,12 @@
 #define MICROPY_ENABLE_EXTERNAL_IMPORT    (0)
 #define MICROPY_KBD_EXCEPTION             (1)
 
+// Use MicroPython's internal printf for HEADLESS and REPL_UART (non-Newlib builds)
+#if (MICROPY_PORT_MODE != MODE_REPL_NEWLIB)
+    #define MICROPY_USE_INTERNAL_PRINTF (1)
+    #define MICROPY_INTERNAL_PRINTF_PRINTER (&mp_plat_print)
+#endif
+
 // MICROPY_MODULE_FROZEN_MPY is automatically defined by the manifest system, when needed
 
 // Enable core modules
@@ -45,7 +58,12 @@
 #define MICROPY_PY_GC                     (1)
 #define MICROPY_PY_BUILTINS_STR_UNICODE   (1)
 
-#define MICROPY_LONGINT_IMPL              (MICROPY_LONGINT_IMPL_LONGLONG)
+// Integer implementation - minimal for HEADLESS and REPL_UART to reduce dependencies
+#if (MICROPY_PORT_MODE == MODE_REPL_NEWLIB)
+    #define MICROPY_LONGINT_IMPL          (MICROPY_LONGINT_IMPL_LONGLONG)
+#else
+    #define MICROPY_LONGINT_IMPL          (MICROPY_LONGINT_IMPL_NONE)
+#endif
 #define MICROPY_PY_BUILTINS_COMPLEX       (0)
 #define MICROPY_PY_IO                     (0)  // no file system or streams
 

advanced/micropython/port-riscv-emu.py/mpconfigport.h

@@ -28,10 +28,12 @@ z_sbss:
     addi a0, a0, 4
     blt  a0, a1, z_sbss
 
+#if (MICROPY_PORT_MODE == MODE_REPL_NEWLIB)
     # initialize Newlib
     la   a0, _impure_ptr
     lw   a0, 0(a0)
     call __sinit
+#endif
 
     # restore a0 and a1
     mv a0, s0