diff --git a/py/dynruntime.h b/py/dynruntime.h
new file mode 100644
index 000000000..34cf6010c
--- /dev/null
+++ b/py/dynruntime.h
@@ -0,0 +1,193 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2019 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_PY_DYNRUNTIME_H
+#define MICROPY_INCLUDED_PY_DYNRUNTIME_H
+
+// This header file contains definitions to dynamically implement the static
+// MicroPython runtime API defined in py/obj.h and py/runtime.h.
+
+#include "py/nativeglue.h"
+#include "py/objstr.h"
+
+#undef MP_ROM_QSTR
+#undef MP_OBJ_QSTR_VALUE
+#undef MP_OBJ_NEW_QSTR
+#undef mp_const_none
+#undef mp_const_false
+#undef mp_const_true
+#undef mp_const_empty_tuple
+#undef nlr_raise
+
+/******************************************************************************/
+// Memory allocation
+
+#define m_malloc(n)                     (m_malloc_dyn((n)))
+#define m_free(ptr)                     (m_free_dyn((ptr)))
+#define m_realloc(ptr, new_num_bytes)   (m_realloc_dyn((ptr), (new_num_bytes)))
+
+static inline void *m_malloc_dyn(size_t n) {
+    // TODO won't raise on OOM
+    return mp_fun_table.realloc_(NULL, n, false);
+}
+
+static inline void m_free_dyn(void *ptr) {
+    mp_fun_table.realloc_(ptr, 0, false);
+}
+
+static inline void *m_realloc_dyn(void *ptr, size_t new_num_bytes) {
+    // TODO won't raise on OOM
+    return mp_fun_table.realloc_(ptr, new_num_bytes, true);
+}
+
+/******************************************************************************/
+// Printing
+
+#define mp_plat_print               (*mp_fun_table.plat_print)
+#define mp_printf(p, ...)           (mp_fun_table.printf_((p), __VA_ARGS__))
+#define mp_vprintf(p, fmt, args)    (mp_fun_table.vprintf_((p), (fmt), (args)))
+
+/******************************************************************************/
+// Types and objects
+
+#define MP_OBJ_NEW_QSTR(x) MP_OBJ_NEW_QSTR_ ## x
+
+#define mp_type_type                        (*mp_fun_table.type_type)
+#define mp_type_str                         (*mp_fun_table.type_str)
+#define mp_type_list                        (*mp_fun_table.type_list)
+#define mp_type_EOFError                    (*(mp_obj_type_t*)(mp_load_global(MP_QSTR_EOFError)))
+#define mp_type_IndexError                  (*(mp_obj_type_t*)(mp_load_global(MP_QSTR_IndexError)))
+#define mp_type_KeyError                    (*(mp_obj_type_t*)(mp_load_global(MP_QSTR_KeyError)))
+#define mp_type_NotImplementedError         (*(mp_obj_type_t*)(mp_load_global(MP_QSTR_NotImplementedError)))
+#define mp_type_RuntimeError                (*(mp_obj_type_t*)(mp_load_global(MP_QSTR_RuntimeError)))
+#define mp_type_TypeError                   (*(mp_obj_type_t*)(mp_load_global(MP_QSTR_TypeError)))
+#define mp_type_ValueError                  (*(mp_obj_type_t*)(mp_load_global(MP_QSTR_ValueError)))
+
+#define mp_stream_read_obj                  (*mp_fun_table.stream_read_obj)
+#define mp_stream_readinto_obj              (*mp_fun_table.stream_readinto_obj)
+#define mp_stream_unbuffered_readline_obj   (*mp_fun_table.stream_unbuffered_readline_obj)
+#define mp_stream_write_obj                 (*mp_fun_table.stream_write_obj)
+
+#define mp_const_none                       ((mp_obj_t)mp_fun_table.const_none)
+#define mp_const_false                      ((mp_obj_t)mp_fun_table.const_false)
+#define mp_const_true                       ((mp_obj_t)mp_fun_table.const_true)
+#define mp_const_empty_tuple                (mp_fun_table.new_tuple(0, NULL))
+
+#define mp_obj_new_bool(b)                  ((b) ? (mp_obj_t)mp_fun_table.const_true : (mp_obj_t)mp_fun_table.const_false)
+#define mp_obj_new_int(i)                   (mp_fun_table.native_to_obj(i, MP_NATIVE_TYPE_INT))
+#define mp_obj_new_str(data, len)           (mp_fun_table.obj_new_str((data), (len)))
+#define mp_obj_new_str_of_type(t, d, l)     (mp_obj_new_str_of_type_dyn((t), (d), (l)))
+#define mp_obj_new_bytes(data, len)         (mp_fun_table.obj_new_bytes((data), (len)))
+#define mp_obj_new_bytearray_by_ref(n, i)   (mp_fun_table.obj_new_bytearray_by_ref((n), (i)))
+#define mp_obj_new_tuple(n, items)          (mp_fun_table.new_tuple((n), (items)))
+#define mp_obj_new_list(n, items)           (mp_fun_table.new_list((n), (items)))
+
+#define mp_obj_get_type(o)                  (mp_fun_table.obj_get_type((o)))
+#define mp_obj_get_int(o)                   (mp_fun_table.native_from_obj(o, MP_NATIVE_TYPE_INT))
+#define mp_obj_str_get_str(s)               ((void*)mp_fun_table.native_from_obj(s, MP_NATIVE_TYPE_PTR))
+#define mp_obj_str_get_data(o, len)         (mp_obj_str_get_data_dyn((o), (len)))
+#define mp_get_buffer_raise(o, bufinfo, fl) (mp_fun_table.get_buffer_raise((o), (bufinfo), (fl)))
+#define mp_get_stream_raise(s, flags)       (mp_fun_table.get_stream_raise((s), (flags)))
+
+#define mp_obj_list_append(list, item)      (mp_fun_table.list_append((list), (item)))
+
+static inline mp_obj_t mp_obj_new_str_of_type_dyn(const mp_obj_type_t *type, const byte* data, size_t len) {
+    if (type == &mp_type_str) {
+        return mp_obj_new_str((const char*)data, len);
+    } else {
+        return mp_obj_new_bytes(data, len);
+    }
+}
+
+static inline void *mp_obj_str_get_data_dyn(mp_obj_t o, size_t *l) {
+    mp_buffer_info_t bufinfo;
+    mp_get_buffer_raise(o, &bufinfo, MP_BUFFER_READ);
+    *l = bufinfo.len;
+    return bufinfo.buf;
+}
+
+/******************************************************************************/
+// General runtime functions
+
+#define mp_load_name(qst)           (mp_fun_table.load_name(qst))
+#define mp_load_global(qst)         (mp_fun_table.load_global(qst))
+#define mp_store_global(qst, obj)   (mp_fun_table.store_global((qst), (obj)))
+#define mp_unary_op(op, obj)        (mp_fun_table.unary_op((op), (obj)))
+#define mp_binary_op(op, lhs, rhs)  (mp_fun_table.binary_op((op), (lhs), (rhs)))
+
+#define mp_make_function_from_raw_code(rc, def_args, def_kw_args) \
+    (mp_fun_table.make_function_from_raw_code((rc), (def_args), (def_kw_args)))
+
+#define mp_call_function_n_kw(fun, n_args, n_kw, args) \
+    (mp_fun_table.call_function_n_kw((fun), (n_args) | ((n_kw) << 8), args))
+
+#define mp_arg_check_num(n_args, n_kw, n_args_min, n_args_max, takes_kw) \
+    (mp_fun_table.arg_check_num_sig((n_args), (n_kw), MP_OBJ_FUN_MAKE_SIG((n_args_min), (n_args_max), (takes_kw))))
+
+#define MP_DYNRUNTIME_INIT_ENTRY \
+    mp_obj_t old_globals = mp_fun_table.swap_globals(self->globals); \
+    mp_raw_code_t rc; \
+    rc.kind = MP_CODE_NATIVE_VIPER; \
+    rc.scope_flags = 0; \
+    rc.const_table = (void*)self->const_table; \
+    (void)rc;
+
+#define MP_DYNRUNTIME_INIT_EXIT \
+    mp_fun_table.swap_globals(old_globals); \
+    return mp_const_none;
+
+#define MP_DYNRUNTIME_MAKE_FUNCTION(f) \
+    (mp_make_function_from_raw_code((rc.fun_data = (f), &rc), MP_OBJ_NULL, MP_OBJ_NULL))
+
+/******************************************************************************/
+// Exceptions
+
+#define mp_obj_new_exception(o)                 ((mp_obj_t)(o)) // Assumes returned object will be raised, will create instance then
+#define mp_obj_new_exception_arg1(e_type, arg)  (mp_obj_new_exception_arg1_dyn((e_type), (arg)))
+
+#define nlr_raise(o)                            (mp_raise_dyn(o))
+#define mp_raise_msg(type, msg)                 (mp_fun_table.raise_msg((type), (msg)))
+#define mp_raise_OSError(er)                    (mp_raise_OSError_dyn(er))
+#define mp_raise_NotImplementedError(msg)       (mp_raise_msg(&mp_type_NotImplementedError, (msg)))
+#define mp_raise_TypeError(msg)                 (mp_raise_msg(&mp_type_TypeError, (msg)))
+#define mp_raise_ValueError(msg)                (mp_raise_msg(&mp_type_ValueError, (msg)))
+
+static inline mp_obj_t mp_obj_new_exception_arg1_dyn(const mp_obj_type_t *exc_type, mp_obj_t arg) {
+    mp_obj_t args[1] = { arg };
+    return mp_call_function_n_kw(MP_OBJ_FROM_PTR(exc_type), 1, 0, &args[0]);
+}
+
+static NORETURN inline void mp_raise_dyn(mp_obj_t o) {
+    mp_fun_table.raise(o);
+    for (;;) {
+    }
+}
+
+static inline void mp_raise_OSError_dyn(int er) {
+    mp_obj_t args[1] = { MP_OBJ_NEW_SMALL_INT(er) };
+    nlr_raise(mp_call_function_n_kw(mp_load_global(MP_QSTR_OSError), 1, 0, &args[0]));
+}
+
+#endif // MICROPY_INCLUDED_PY_DYNRUNTIME_H
diff --git a/py/dynruntime.mk b/py/dynruntime.mk
new file mode 100644
index 000000000..b01b80e0d
--- /dev/null
+++ b/py/dynruntime.mk
@@ -0,0 +1,134 @@
+# Makefile fragment for generating native .mpy files from C source
+# MPY_DIR must be set to the top of the MicroPython source tree
+
+BUILD ?= build
+
+ECHO = @echo
+RM = /bin/rm
+MKDIR = /bin/mkdir
+PYTHON = python3
+MPY_CROSS = $(MPY_DIR)/mpy-cross/mpy-cross
+MPY_TOOL = $(PYTHON) $(MPY_DIR)/tools/mpy-tool.py
+MPY_LD = $(PYTHON) $(MPY_DIR)/tools/mpy_ld.py
+
+Q = @
+ifeq ("$(origin V)", "command line")
+ifeq ($(V),1)
+Q =
+MPY_LD += '-vvv'
+endif
+endif
+
+ARCH_UPPER = $(shell echo $(ARCH) | tr '[:lower:]' '[:upper:]')
+CONFIG_H = $(BUILD)/$(MOD).config.h
+
+CFLAGS += -I. -I$(MPY_DIR)
+CFLAGS += -std=c99
+CFLAGS += -Os
+CFLAGS += -Wall -Werror -DNDEBUG
+CFLAGS += -DNO_QSTR
+CFLAGS += -DMP_CONFIGFILE='<$(CONFIG_H)>'
+CFLAGS += -fpic -fno-common
+CFLAGS += -U _FORTIFY_SOURCE # prevent use of __*_chk libc functions
+#CFLAGS += -fdata-sections -ffunction-sections
+
+MPY_CROSS_FLAGS += -march=$(ARCH)
+
+SRC_O += $(addprefix $(BUILD)/, $(patsubst %.c,%.o,$(filter %.c,$(SRC))))
+SRC_MPY += $(addprefix $(BUILD)/, $(patsubst %.py,%.mpy,$(filter %.py,$(SRC))))
+
+################################################################################
+# Architecture configuration
+
+ifeq ($(ARCH),x86)
+
+# x86
+CROSS =
+CFLAGS += -m32 -fno-stack-protector
+MPY_CROSS_FLAGS += -mcache-lookup-bc
+
+else ifeq ($(ARCH),x64)
+
+# x64
+CROSS =
+CFLAGS += -fno-stack-protector
+MPY_CROSS_FLAGS += -mcache-lookup-bc
+
+else ifeq ($(ARCH),armv7m)
+
+# thumb
+CROSS = arm-none-eabi-
+CFLAGS += -mthumb -mcpu=cortex-m3
+
+else ifeq ($(ARCH),armv7emsp)
+
+# thumb
+CROSS = arm-none-eabi-
+CFLAGS += -mthumb -mcpu=cortex-m4
+CFLAGS += -mfpu=fpv4-sp-d16 -mfloat-abi=hard
+
+else ifeq ($(ARCH),armv7emdp)
+
+# thumb
+CROSS = arm-none-eabi-
+CFLAGS += -mthumb -mcpu=cortex-m7
+CFLAGS += -mfpu=fpv5-d16 -mfloat-abi=hard
+
+else ifeq ($(ARCH),xtensa)
+
+# xtensa
+CROSS = xtensa-lx106-elf-
+CFLAGS += -mforce-l32
+
+else ifeq ($(ARCH),xtensawin)
+
+# xtensawin
+CROSS = xtensa-esp32-elf-
+CFLAGS +=
+
+else
+$(error architecture '$(ARCH)' not supported)
+endif
+
+CFLAGS += $(CFLAGS_EXTRA)
+
+################################################################################
+# Build rules
+
+.PHONY: all clean
+
+all: $(MOD).mpy
+
+clean:
+	$(RM) -rf $(BUILD) $(CLEAN_EXTRA)
+
+# Create build destination directories first
+BUILD_DIRS = $(sort $(dir $(CONFIG_H) $(SRC_O) $(SRC_MPY)))
+$(CONFIG_H) $(SRC_O) $(SRC_MPY): | $(BUILD_DIRS)
+$(BUILD_DIRS):
+	$(Q)$(MKDIR) -p $@
+
+# Preprocess all source files to generate $(CONFIG_H)
+$(CONFIG_H): $(SRC)
+	$(ECHO) "GEN $@"
+	$(Q)$(MPY_LD) --arch $(ARCH) --preprocess -o $@ $^
+
+# Build .o from .c source files
+$(BUILD)/%.o: %.c $(CONFIG_H) Makefile
+	$(ECHO) "CC $<"
+	$(Q)$(CROSS)gcc $(CFLAGS) -o $@ -c $<
+
+# Build .mpy from .py source files
+$(BUILD)/%.mpy: %.py
+	$(ECHO) "MPY $<"
+	$(Q)$(MPY_CROSS) $(MPY_CROSS_FLAGS) -o $@ $<
+
+# Build native .mpy from object files
+$(BUILD)/$(MOD).native.mpy: $(SRC_O)
+	$(ECHO) "LINK $<"
+	$(Q)$(MPY_LD) --arch $(ARCH) --qstrs $(CONFIG_H) -o $@ $^
+
+# Build final .mpy from all intermediate .mpy files
+$(MOD).mpy: $(BUILD)/$(MOD).native.mpy $(SRC_MPY)
+	$(ECHO) "GEN $@"
+	$(Q)$(MPY_TOOL) --merge -o $@ $^
diff --git a/tools/mpy_ld.py b/tools/mpy_ld.py
new file mode 100755
index 000000000..07105caac
--- /dev/null
+++ b/tools/mpy_ld.py
@@ -0,0 +1,978 @@
+#!/usr/bin/env python3
+#
+# This file is part of the MicroPython project, http://micropython.org/
+#
+# The MIT License (MIT)
+#
+# Copyright (c) 2019 Damien P. George
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+"""
+Link .o files to .mpy
+"""
+
+import sys, os, struct, re
+from elftools.elf import elffile
+
+sys.path.append(os.path.dirname(__file__) + '/../py')
+import makeqstrdata as qstrutil
+
+# MicroPython constants
+MPY_VERSION = 5
+MP_NATIVE_ARCH_X86 = 1
+MP_NATIVE_ARCH_X64 = 2
+MP_NATIVE_ARCH_ARMV7M = 5
+MP_NATIVE_ARCH_ARMV7EMSP = 7
+MP_NATIVE_ARCH_ARMV7EMDP = 8
+MP_NATIVE_ARCH_XTENSA = 9
+MP_NATIVE_ARCH_XTENSAWIN = 10
+MP_CODE_BYTECODE = 2
+MP_CODE_NATIVE_VIPER = 4
+MP_SCOPE_FLAG_VIPERRELOC = 0x10
+MP_SCOPE_FLAG_VIPERRODATA = 0x20
+MP_SCOPE_FLAG_VIPERBSS = 0x40
+MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE = 1
+MICROPY_PY_BUILTINS_STR_UNICODE = 2
+MP_SMALL_INT_BITS = 31
+QSTR_WINDOW_SIZE = 32
+
+# ELF constants
+R_386_32 = 1
+R_X86_64_64 = 1
+R_XTENSA_32 = 1
+R_386_PC32 = 2
+R_X86_64_PC32 = 2
+R_ARM_ABS32 = 2
+R_386_GOT32 = 3
+R_ARM_REL32 = 3
+R_386_PLT32 = 4
+R_X86_64_PLT32 = 4
+R_XTENSA_PLT = 6
+R_386_GOTOFF = 9
+R_386_GOTPC = 10
+R_ARM_THM_CALL = 10
+R_XTENSA_DIFF32 = 19
+R_XTENSA_SLOT0_OP = 20
+R_ARM_BASE_PREL = 25 # aka R_ARM_GOTPC
+R_ARM_GOT_BREL = 26 # aka R_ARM_GOT32
+R_ARM_THM_JUMP24 = 30
+R_X86_64_REX_GOTPCRELX = 42
+R_386_GOT32X = 43
+
+################################################################################
+# Architecture configuration
+
+def asm_jump_x86(entry):
+    return struct.pack('<BI', 0xe9, entry - 5)
+
+def asm_jump_arm(entry):
+    b_off = entry - 4
+    if b_off >> 11 == 0 or b_off >> 11 == -1:
+        # Signed value fits in 12 bits
+        b0 = 0xe000 | (b_off >> 1 & 0x07ff)
+        b1 = 0
+    else:
+        # Use large jump
+        b0 = 0xf000 | (b_off >> 12 & 0x07ff)
+        b1 = 0xb800 | (b_off >> 1 & 0x7ff)
+    return struct.pack('<HH', b0, b1)
+
+def asm_jump_xtensa(entry):
+    jump_offset = entry - 4
+    jump_op = jump_offset << 6 | 6
+    return struct.pack('<BH', jump_op & 0xff, jump_op >> 8)
+
+class ArchData:
+    def __init__(self, name, mpy_feature, qstr_entry_size, word_size, arch_got, asm_jump):
+        self.name = name
+        self.mpy_feature = mpy_feature
+        self.qstr_entry_size = qstr_entry_size
+        self.word_size = word_size
+        self.arch_got = arch_got
+        self.asm_jump = asm_jump
+        self.separate_rodata = name == 'EM_XTENSA' and qstr_entry_size == 4
+
+ARCH_DATA = {
+    'x86': ArchData(
+        'EM_386',
+        MP_NATIVE_ARCH_X86 << 2 | MICROPY_PY_BUILTINS_STR_UNICODE | MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE,
+        2, 4, (R_386_PC32, R_386_GOT32, R_386_GOT32X), asm_jump_x86,
+    ),
+    'x64': ArchData(
+        'EM_X86_64',
+        MP_NATIVE_ARCH_X64 << 2 | MICROPY_PY_BUILTINS_STR_UNICODE | MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE,
+        2, 8, (R_X86_64_REX_GOTPCRELX,), asm_jump_x86,
+    ),
+    'armv7m': ArchData(
+        'EM_ARM',
+        MP_NATIVE_ARCH_ARMV7M << 2 | MICROPY_PY_BUILTINS_STR_UNICODE,
+        2, 4, (R_ARM_GOT_BREL,), asm_jump_arm,
+    ),
+    'armv7emsp': ArchData(
+        'EM_ARM',
+        MP_NATIVE_ARCH_ARMV7EMSP << 2 | MICROPY_PY_BUILTINS_STR_UNICODE,
+        2, 4, (R_ARM_GOT_BREL,), asm_jump_arm,
+    ),
+    'armv7emdp': ArchData(
+        'EM_ARM',
+        MP_NATIVE_ARCH_ARMV7EMDP << 2 | MICROPY_PY_BUILTINS_STR_UNICODE,
+        2, 4, (R_ARM_GOT_BREL,), asm_jump_arm,
+    ),
+    'xtensa': ArchData(
+        'EM_XTENSA',
+        MP_NATIVE_ARCH_XTENSA << 2 | MICROPY_PY_BUILTINS_STR_UNICODE,
+        2, 4, (R_XTENSA_32, R_XTENSA_PLT), asm_jump_xtensa,
+    ),
+    'xtensawin': ArchData(
+        'EM_XTENSA',
+        MP_NATIVE_ARCH_XTENSAWIN << 2 | MICROPY_PY_BUILTINS_STR_UNICODE,
+        4, 4, (R_XTENSA_32, R_XTENSA_PLT), asm_jump_xtensa,
+    ),
+}
+
+################################################################################
+# Helper functions
+
+def align_to(value, align):
+    return (value + align - 1) & ~(align - 1)
+
+def unpack_u24le(data, offset):
+    return data[offset] | data[offset + 1] << 8 | data[offset + 2] << 16
+
+def pack_u24le(data, offset, value):
+    data[offset] = value & 0xff
+    data[offset + 1] = value >> 8 & 0xff
+    data[offset + 2] = value >> 16 & 0xff
+
+def xxd(text):
+    for i in range(0, len(text), 16):
+        print('{:08x}:'.format(i), end='')
+        for j in range(4):
+            off = i + j * 4
+            if off < len(text):
+                d = int.from_bytes(text[off:off + 4], 'little')
+                print(' {:08x}'.format(d), end='')
+        print()
+
+# Smaller numbers are enabled first
+LOG_LEVEL_1 = 1
+LOG_LEVEL_2 = 2
+LOG_LEVEL_3 = 3
+log_level = LOG_LEVEL_1
+
+def log(level, msg):
+    if level <= log_level:
+        print(msg)
+
+################################################################################
+# Qstr extraction
+
+def extract_qstrs(source_files):
+    def read_qstrs(f):
+        with open(f) as f:
+            vals = set()
+            objs = set()
+            for line in f:
+                while line:
+                    m = re.search(r'MP_OBJ_NEW_QSTR\((MP_QSTR_[A-Za-z0-9_]*)\)', line)
+                    if m:
+                        objs.add(m.group(1))
+                    else:
+                        m = re.search(r'MP_QSTR_[A-Za-z0-9_]*', line)
+                        if m:
+                            vals.add(m.group())
+                    if m:
+                        s = m.span()
+                        line = line[:s[0]] + line[s[1]:]
+                    else:
+                        line = ''
+            return vals, objs
+
+    static_qstrs = ['MP_QSTR_' + qstrutil.qstr_escape(q) for q in qstrutil.static_qstr_list]
+
+    qstr_vals = set()
+    qstr_objs = set()
+    for f in source_files:
+        vals, objs = read_qstrs(f)
+        qstr_vals.update(vals)
+        qstr_objs.update(objs)
+    qstr_vals.difference_update(static_qstrs)
+
+    return static_qstrs, qstr_vals, qstr_objs
+
+################################################################################
+# Linker
+
+class LinkError(Exception):
+    pass
+
+class Section:
+    def __init__(self, name, data, alignment, filename=None):
+        self.filename = filename
+        self.name = name
+        self.data = data
+        self.alignment = alignment
+        self.addr = 0
+        self.reloc = []
+
+    @staticmethod
+    def from_elfsec(elfsec, filename):
+        assert elfsec.header.sh_addr == 0
+        return Section(elfsec.name, elfsec.data(), elfsec.data_alignment, filename)
+
+class GOTEntry:
+    def __init__(self, name, sym, link_addr=0):
+        self.name = name
+        self.sym = sym
+        self.offset = None
+        self.link_addr = link_addr
+
+    def isexternal(self):
+        return self.sec_name.startswith('.external')
+
+    def istext(self):
+        return self.sec_name.startswith('.text')
+
+    def isrodata(self):
+        return self.sec_name.startswith(('.rodata', '.data.rel.ro'))
+
+    def isbss(self):
+        return self.sec_name.startswith('.bss')
+
+class LiteralEntry:
+    def __init__(self, value, offset):
+        self.value = value
+        self.offset = offset
+
+class LinkEnv:
+    def __init__(self, arch):
+        self.arch = ARCH_DATA[arch]
+        self.sections = []          # list of sections in order of output
+        self.literal_sections = []  # list of literal sections (xtensa only)
+        self.known_syms = {}        # dict of symbols that are defined
+        self.unresolved_syms = []   # list of unresolved symbols
+        self.mpy_relocs = []        # list of relocations needed in the output .mpy file
+
+    def check_arch(self, arch_name):
+        if arch_name != self.arch.name:
+            raise LinkError('incompatible arch')
+
+    def print_sections(self):
+        log(LOG_LEVEL_2, 'sections:')
+        for sec in self.sections:
+            log(LOG_LEVEL_2, '  {:08x} {} size={}'.format(sec.addr, sec.name, len(sec.data)))
+
+    def find_addr(self, name):
+        if name in self.known_syms:
+            s = self.known_syms[name]
+            return s.section.addr + s['st_value']
+        raise LinkError('unknown symbol: {}'.format(name))
+
+def build_got_generic(env):
+    env.got_entries = {}
+    for sec in env.sections:
+        for r in sec.reloc:
+            s = r.sym
+            if not (s.entry['st_info']['bind'] == 'STB_GLOBAL' and r['r_info_type'] in env.arch.arch_got):
+                continue
+            s_type = s.entry['st_info']['type']
+            assert s_type in ('STT_NOTYPE', 'STT_FUNC', 'STT_OBJECT'), s_type
+            assert s.name
+            if s.name in env.got_entries:
+                continue
+            env.got_entries[s.name] = GOTEntry(s.name, s)
+
+def build_got_xtensa(env):
+    env.got_entries = {}
+    env.lit_entries = {}
+    env.xt_literals = {}
+
+    # Extract the values from the literal table
+    for sec in env.literal_sections:
+        assert len(sec.data) % env.arch.word_size == 0
+
+        # Look through literal relocations to find any global pointers that should be GOT entries
+        for r in sec.reloc:
+            s = r.sym
+            s_type = s.entry['st_info']['type']
+            assert s_type in ('STT_NOTYPE', 'STT_FUNC', 'STT_OBJECT', 'STT_SECTION'), s_type
+            assert r['r_info_type'] in env.arch.arch_got
+            assert r['r_offset'] % env.arch.word_size == 0
+            # This entry is a global pointer
+            existing = struct.unpack_from('<I', sec.data, r['r_offset'])[0]
+            if s_type == 'STT_SECTION':
+                assert r['r_addend'] == 0
+                name = "{}+0x{:x}".format(s.section.name, existing)
+            else:
+                assert existing == 0
+                name = s.name
+                if r['r_addend'] != 0:
+                    name = "{}+0x{:x}".format(name, r['r_addend'])
+            idx = '{}+0x{:x}'.format(sec.filename, r['r_offset'])
+            env.xt_literals[idx] = name
+            if name in env.got_entries:
+                # Deduplicate GOT entries
+                continue
+            env.got_entries[name] = GOTEntry(name, s, existing)
+
+        # Go through all literal entries finding those that aren't global pointers so must be actual literals
+        for i in range(0, len(sec.data), env.arch.word_size):
+            idx = '{}+0x{:x}'.format(sec.filename, i)
+            if idx not in env.xt_literals:
+                # This entry is an actual literal
+                value = struct.unpack_from('<I', sec.data, i)[0]
+                env.xt_literals[idx] = value
+                if value in env.lit_entries:
+                    # Deduplicate literals
+                    continue
+                env.lit_entries[value] = LiteralEntry(value, len(env.lit_entries) * env.arch.word_size)
+
+def populate_got(env):
+    # Compute GOT destination addresses
+    for got_entry in env.got_entries.values():
+        sym = got_entry.sym
+        if hasattr(sym, 'resolved'):
+            sym = sym.resolved
+        sec = sym.section
+        addr = sym['st_value']
+        got_entry.sec_name = sec.name
+        got_entry.link_addr += sec.addr + addr
+
+    # Get sorted GOT, sorted by external, text, rodata, bss so relocations can be combined
+    got_list = sorted(env.got_entries.values(),
+        key=lambda g: g.isexternal() + 2 * g.istext() + 3 * g.isrodata() + 4 * g.isbss())
+
+    # Layout and populate the GOT
+    offset = 0
+    for got_entry in got_list:
+        got_entry.offset = offset
+        offset += env.arch.word_size
+        o = env.got_section.addr + got_entry.offset
+        env.full_text[o:o + env.arch.word_size] = got_entry.link_addr.to_bytes(env.arch.word_size, 'little')
+
+    # Create a relocation for each GOT entry
+    for got_entry in got_list:
+        if got_entry.name == 'mp_fun_table':
+            dest = 'mp_fun_table'
+        elif got_entry.name.startswith('mp_fun_table+0x'):
+            dest = int(got_entry.name.split('+')[1], 16) // env.arch.word_size
+        elif got_entry.sec_name.startswith('.text'):
+            dest = '.text'
+        elif got_entry.sec_name.startswith('.rodata'):
+            dest = '.rodata'
+        elif got_entry.sec_name.startswith('.data.rel.ro'):
+            dest = '.data.rel.ro'
+        elif got_entry.sec_name.startswith('.bss'):
+            dest = '.bss'
+        else:
+            assert 0, (got_entry.name, got_entry.sec_name)
+        env.mpy_relocs.append(('.text', env.got_section.addr + got_entry.offset, dest))
+
+    # Print out the final GOT
+    log(LOG_LEVEL_2, 'GOT: {:08x}'.format(env.got_section.addr))
+    for g in got_list:
+        log(LOG_LEVEL_2, '  {:08x} {} -> {}+{:08x}'.format(g.offset, g.name, g.sec_name, g.link_addr))
+
+def populate_lit(env):
+    log(LOG_LEVEL_2, 'LIT: {:08x}'.format(env.lit_section.addr))
+    for lit_entry in env.lit_entries.values():
+        value = lit_entry.value
+        log(LOG_LEVEL_2, '  {:08x} = {:08x}'.format(lit_entry.offset, value))
+        o = env.lit_section.addr + lit_entry.offset
+        env.full_text[o:o + env.arch.word_size] = value.to_bytes(env.arch.word_size, 'little')
+
+def do_relocation_text(env, text_addr, r):
+    # Extract relevant info about symbol that's being relocated
+    s = r.sym
+    s_bind = s.entry['st_info']['bind']
+    s_shndx = s.entry['st_shndx']
+    s_type = s.entry['st_info']['type']
+    r_offset = r['r_offset'] + text_addr
+    r_info_type = r['r_info_type']
+    try:
+        # only for RELA sections
+        r_addend = r['r_addend']
+    except KeyError:
+        r_addend = 0
+
+    # Default relocation type and name for logging
+    reloc_type = 'le32'
+    log_name = None
+
+    if (env.arch.name == 'EM_386' and r_info_type in (R_386_PC32, R_386_PLT32)
+        or env.arch.name == 'EM_X86_64' and r_info_type in (R_X86_64_PC32, R_X86_64_PLT32)
+        or env.arch.name == 'EM_ARM' and r_info_type in (R_ARM_REL32, R_ARM_THM_CALL, R_ARM_THM_JUMP24)
+        or s_bind == 'STB_LOCAL' and env.arch.name == 'EM_XTENSA' and r_info_type == R_XTENSA_32 # not GOT
+        ):
+        # Standard relocation to fixed location within text/rodata
+        if hasattr(s, 'resolved'):
+            s = s.resolved
+
+        sec = s.section
+
+        if env.arch.separate_rodata and sec.name.startswith('.rodata'):
+            raise LinkError('fixed relocation to rodata with rodata referenced via GOT')
+
+        if sec.name.startswith('.bss'):
+            raise LinkError('{}: fixed relocation to bss (bss variables can\'t be static)'.format(s.filename))
+
+        if sec.name.startswith('.external'):
+            raise LinkError('{}: fixed relocation to external symbol: {}'.format(s.filename, s.name))
+
+        addr = sec.addr + s['st_value']
+        reloc = addr - r_offset + r_addend
+
+        if r_info_type in (R_ARM_THM_CALL, R_ARM_THM_JUMP24):
+            # Both relocations have the same bit pattern to rewrite:
+            #   R_ARM_THM_CALL: bl
+            #   R_ARM_THM_JUMP24: b.w
+            reloc_type = 'thumb_b'
+
+    elif (env.arch.name == 'EM_386' and r_info_type == R_386_GOTPC
+        or env.arch.name == 'EM_ARM' and r_info_type == R_ARM_BASE_PREL
+        ):
+        # Relocation to GOT address itself
+        assert s.name == '_GLOBAL_OFFSET_TABLE_'
+        addr = env.got_section.addr
+        reloc = addr - r_offset + r_addend
+
+    elif (env.arch.name == 'EM_386' and r_info_type in (R_386_GOT32, R_386_GOT32X)
+        or env.arch.name == 'EM_ARM' and r_info_type == R_ARM_GOT_BREL
+        ):
+        # Relcation pointing to GOT
+        reloc = addr = env.got_entries[s.name].offset
+
+    elif env.arch.name == 'EM_X86_64' and r_info_type == R_X86_64_REX_GOTPCRELX:
+        # Relcation pointing to GOT
+        got_entry = env.got_entries[s.name]
+        addr = env.got_section.addr + got_entry.offset
+        reloc = addr - r_offset + r_addend
+
+    elif env.arch.name == 'EM_386' and r_info_type == R_386_GOTOFF:
+        # Relocation relative to GOT
+        addr = s.section.addr + s['st_value']
+        reloc = addr - env.got_section.addr + r_addend
+
+    elif env.arch.name == 'EM_XTENSA' and r_info_type == R_XTENSA_SLOT0_OP:
+        # Relocation pointing to GOT, xtensa specific
+        sec = s.section
+        if sec.name.startswith('.text'):
+            # it looks like R_XTENSA_SLOT0_OP into .text is already correctly relocated
+            return
+        assert sec.name.startswith('.literal'), sec.name
+        lit_idx = '{}+0x{:x}'.format(sec.filename, r_addend)
+        lit_ptr = env.xt_literals[lit_idx]
+        if isinstance(lit_ptr, str):
+            addr = env.got_section.addr + env.got_entries[lit_ptr].offset
+            log_name = 'GOT {}'.format(lit_ptr)
+        else:
+            addr = env.lit_section.addr + env.lit_entries[lit_ptr].offset
+            log_name = 'LIT'
+        reloc = addr - r_offset
+        reloc_type = 'xtensa_l32r'
+
+    elif env.arch.name == 'EM_XTENSA' and r_info_type == R_XTENSA_DIFF32:
+        if s.section.name.startswith('.text'):
+            # it looks like R_XTENSA_DIFF32 into .text is already correctly relocated
+            return
+        assert 0
+
+    else:
+        # Unknown/unsupported relocation
+        assert 0, r_info_type
+
+    # Write relocation
+    if reloc_type == 'le32':
+        existing, = struct.unpack_from('<I', env.full_text, r_offset)
+        struct.pack_into('<I', env.full_text, r_offset, (existing + reloc) & 0xffffffff)
+    elif reloc_type == 'thumb_b':
+        b_h, b_l = struct.unpack_from('<HH', env.full_text, r_offset)
+        existing = (b_h & 0x7ff) << 12 | (b_l & 0x7ff) << 1
+        if existing >= 0x400000: # 2's complement
+            existing -= 0x800000
+        new = existing + reloc
+        b_h = (b_h & 0xf800) | (new >> 12) & 0x7ff
+        b_l = (b_l & 0xf800) | (new >> 1) & 0x7ff
+        struct.pack_into('<HH', env.full_text, r_offset, b_h, b_l)
+    elif reloc_type == 'xtensa_l32r':
+        l32r = unpack_u24le(env.full_text, r_offset)
+        assert l32r & 0xf == 1 # RI16 encoded l32r
+        l32r_imm16 = l32r >> 8
+        l32r_imm16 = (l32r_imm16 + reloc >> 2) & 0xffff
+        l32r = l32r & 0xff | l32r_imm16 << 8
+        pack_u24le(env.full_text, r_offset, l32r)
+    else:
+        assert 0, reloc_type
+
+    # Log information about relocation
+    if log_name is None:
+        if s_type == 'STT_SECTION':
+            log_name = s.section.name
+        else:
+            log_name = s.name
+    log(LOG_LEVEL_3, '  {:08x} {} -> {:08x}'.format(r_offset, log_name, addr))
+
+def do_relocation_data(env, text_addr, r):
+    s = r.sym
+    s_type = s.entry['st_info']['type']
+    r_offset = r['r_offset'] + text_addr
+    r_info_type = r['r_info_type']
+    try:
+        # only for RELA sections
+        r_addend = r['r_addend']
+    except KeyError:
+        r_addend = 0
+
+    if (env.arch.name == 'EM_386' and r_info_type == R_386_32
+        or env.arch.name == 'EM_X86_64' and r_info_type == R_X86_64_64
+        or env.arch.name == 'EM_ARM' and r_info_type == R_ARM_ABS32
+        or env.arch.name == 'EM_XTENSA' and r_info_type == R_XTENSA_32):
+        # Relocation in data.rel.ro to internal/external symbol
+        if env.arch.word_size == 4:
+            struct_type = '<I'
+        elif env.arch.word_size == 8:
+            struct_type = '<Q'
+        sec = s.section
+        assert r_offset % env.arch.word_size == 0
+        addr = sec.addr + s['st_value'] + r_addend
+        if s_type == 'STT_SECTION':
+            log_name = sec.name
+        else:
+            log_name = s.name
+        log(LOG_LEVEL_3, '  {:08x} -> {} {:08x}'.format(r_offset, log_name, addr))
+        if env.arch.separate_rodata:
+            data = env.full_rodata
+        else:
+            data = env.full_text
+        existing, = struct.unpack_from(struct_type, data, r_offset)
+        if sec.name.startswith(('.text', '.rodata', '.data.rel.ro', '.bss')):
+            struct.pack_into(struct_type, data, r_offset, existing + addr)
+            kind = sec.name
+        elif sec.name == '.external.mp_fun_table':
+            assert addr == 0
+            kind = s.mp_fun_table_offset
+        else:
+            assert 0, sec.name
+        if env.arch.separate_rodata:
+            base = '.rodata'
+        else:
+            base = '.text'
+        env.mpy_relocs.append((base, r_offset, kind))
+
+    else:
+        # Unknown/unsupported relocation
+        assert 0, r_info_type
+
+def load_object_file(env, felf):
+    with open(felf, 'rb') as f:
+        elf = elffile.ELFFile(f)
+        env.check_arch(elf['e_machine'])
+
+        # Get symbol table
+        symtab = list(elf.get_section_by_name('.symtab').iter_symbols())
+
+        # Load needed sections from ELF file
+        sections_shndx = {} # maps elf shndx to Section object
+        for idx, s in enumerate(elf.iter_sections()):
+            if s.header.sh_type in ('SHT_PROGBITS', 'SHT_NOBITS'):
+                if s.data_size == 0:
+                    # Ignore empty sections
+                    pass
+                elif s.name.startswith(('.literal', '.text', '.rodata', '.data.rel.ro', '.bss')):
+                    sec = Section.from_elfsec(s, felf)
+                    sections_shndx[idx] = sec
+                    if s.name.startswith('.literal'):
+                        env.literal_sections.append(sec)
+                    else:
+                        env.sections.append(sec)
+                elif s.name.startswith('.data'):
+                    raise LinkError('{}: {} non-empty'.format(felf, s.name))
+                else:
+                    # Ignore section
+                    pass
+            elif s.header.sh_type in ('SHT_REL', 'SHT_RELA'):
+                shndx = s.header.sh_info
+                if shndx in sections_shndx:
+                    sec = sections_shndx[shndx]
+                    sec.reloc_name = s.name
+                    sec.reloc = list(s.iter_relocations())
+                    for r in sec.reloc:
+                        r.sym = symtab[r['r_info_sym']]
+
+        # Link symbols to their sections, and update known and unresolved symbols
+        for sym in symtab:
+            sym.filename = felf
+            shndx = sym.entry['st_shndx']
+            if shndx in sections_shndx:
+                # Symbol with associated section
+                sym.section = sections_shndx[shndx]
+                if sym['st_info']['bind'] == 'STB_GLOBAL':
+                    # Defined global symbol
+                    if sym.name in env.known_syms and not sym.name.startswith('__x86.get_pc_thunk.'):
+                        raise LinkError('duplicate symbol: {}'.format(sym.name))
+                    env.known_syms[sym.name] = sym
+            elif sym.entry['st_shndx'] == 'SHN_UNDEF' and sym['st_info']['bind'] == 'STB_GLOBAL':
+                # Undefined global symbol, needs resolving
+                env.unresolved_syms.append(sym)
+
+def link_objects(env, native_qstr_vals_len, native_qstr_objs_len):
+    # Build GOT information
+    if env.arch.name == 'EM_XTENSA':
+        build_got_xtensa(env)
+    else:
+        build_got_generic(env)
+
+    # Creat GOT section
+    got_size = len(env.got_entries) * env.arch.word_size
+    env.got_section = Section('GOT', bytearray(got_size), env.arch.word_size)
+    if env.arch.name == 'EM_XTENSA':
+        env.sections.insert(0, env.got_section)
+    else:
+        env.sections.append(env.got_section)
+
+    # Create optional literal section
+    if env.arch.name == 'EM_XTENSA':
+        lit_size = len(env.lit_entries) * env.arch.word_size
+        env.lit_section = Section('LIT', bytearray(lit_size), env.arch.word_size)
+        env.sections.insert(1, env.lit_section)
+
+    # Create section to contain mp_native_qstr_val_table
+    env.qstr_val_section = Section('.text.QSTR_VAL', bytearray(native_qstr_vals_len * env.arch.qstr_entry_size), env.arch.qstr_entry_size)
+    env.sections.append(env.qstr_val_section)
+
+    # Create section to contain mp_native_qstr_obj_table
+    env.qstr_obj_section = Section('.text.QSTR_OBJ', bytearray(native_qstr_objs_len * env.arch.word_size), env.arch.word_size)
+    env.sections.append(env.qstr_obj_section)
+
+    # Resolve unknown symbols
+    mp_fun_table_sec = Section('.external.mp_fun_table', b'', 0)
+    fun_table = {key: 63 + idx
+        for idx, key in enumerate([
+            'mp_type_type',
+            'mp_type_str',
+            'mp_type_list',
+            'mp_type_dict',
+            'mp_type_fun_builtin_0',
+            'mp_type_fun_builtin_1',
+            'mp_type_fun_builtin_2',
+            'mp_type_fun_builtin_3',
+            'mp_type_fun_builtin_var',
+            'mp_stream_read_obj',
+            'mp_stream_readinto_obj',
+            'mp_stream_unbuffered_readline_obj',
+            'mp_stream_write_obj',
+        ])
+    }
+    for sym in env.unresolved_syms:
+        assert sym['st_value'] == 0
+        if sym.name == '_GLOBAL_OFFSET_TABLE_':
+            pass
+        elif sym.name == 'mp_fun_table':
+            sym.section = Section('.external', b'', 0)
+        elif sym.name == 'mp_native_qstr_val_table':
+            sym.section = env.qstr_val_section
+        elif sym.name == 'mp_native_qstr_obj_table':
+            sym.section = env.qstr_obj_section
+        elif sym.name in env.known_syms:
+            sym.resolved = env.known_syms[sym.name]
+        else:
+            if sym.name in fun_table:
+                sym.section = mp_fun_table_sec
+                sym.mp_fun_table_offset = fun_table[sym.name]
+            else:
+                raise LinkError('{}: undefined symbol: {}'.format(sym.filename, sym.name))
+
+    # Align sections, assign their addresses, and create full_text
+    env.full_text = bytearray(env.arch.asm_jump(8)) # dummy, to be filled in later
+    env.full_rodata = bytearray(0)
+    env.full_bss = bytearray(0)
+    for sec in env.sections:
+        if env.arch.separate_rodata and sec.name.startswith(('.rodata', '.data.rel.ro')):
+            data = env.full_rodata
+        elif sec.name.startswith('.bss'):
+            data = env.full_bss
+        else:
+            data = env.full_text
+        sec.addr = align_to(len(data), sec.alignment)
+        data.extend(b'\x00' * (sec.addr - len(data)))
+        data.extend(sec.data)
+
+    env.print_sections()
+
+    populate_got(env)
+    if env.arch.name == 'EM_XTENSA':
+        populate_lit(env)
+
+    # Fill in relocations
+    for sec in env.sections:
+        if not sec.reloc:
+            continue
+        log(LOG_LEVEL_3, '{}: {} relocations via {}:'.format(sec.filename, sec.name, sec.reloc_name))
+        for r in sec.reloc:
+            if sec.name.startswith(('.text', '.rodata')):
+                do_relocation_text(env, sec.addr, r)
+            elif sec.name.startswith('.data.rel.ro'):
+                do_relocation_data(env, sec.addr, r)
+            else:
+                assert 0, sec.name
+
+################################################################################
+# .mpy output
+
+class MPYOutput:
+    def open(self, fname):
+        self.f = open(fname, 'wb')
+        self.prev_base = -1
+        self.prev_offset = -1
+
+    def close(self):
+        self.f.close()
+
+    def write_bytes(self, buf):
+        self.f.write(buf)
+
+    def write_uint(self, val):
+        b = bytearray()
+        b.insert(0, val & 0x7f)
+        val >>= 7
+        while val:
+            b.insert(0, 0x80 | (val & 0x7f))
+            val >>= 7
+        self.write_bytes(b)
+
+    def write_qstr(self, s):
+        if s in qstrutil.static_qstr_list:
+            self.write_bytes(bytes([0, qstrutil.static_qstr_list.index(s) + 1]))
+        else:
+            s = bytes(s, 'ascii')
+            self.write_uint(len(s) << 1)
+            self.write_bytes(s)
+
+    def write_obj(self, o):
+        if o is Ellipsis:
+            self.write_bytes(b'e')
+            return
+        else:
+            # Other Python types not implemented
+            assert 0
+
+    def write_reloc(self, base, offset, dest, n):
+        need_offset = not (base == self.prev_base and offset == self.prev_offset + 1)
+        self.prev_offset = offset + n - 1
+        if dest <= 2:
+            dest = (dest << 1) | (n > 1)
+        else:
+            assert 6 <= dest <= 127
+            assert n == 1
+        dest = dest << 1 | need_offset
+        assert 0 <= dest <= 0xfe, dest
+        self.write_bytes(bytes([dest]))
+        if need_offset:
+            if base == '.text':
+                base = 0
+            elif base == '.rodata':
+                base = 1
+            self.write_uint(offset << 1 | base)
+        if n > 1:
+            self.write_uint(n)
+
+def build_mpy(env, entry_offset, fmpy, native_qstr_vals, native_qstr_objs):
+    # Write jump instruction to start of text
+    jump = env.arch.asm_jump(entry_offset)
+    env.full_text[:len(jump)] = jump
+
+    log(LOG_LEVEL_1, 'arch:         {}'.format(env.arch.name))
+    log(LOG_LEVEL_1, 'text size:    {}'.format(len(env.full_text)))
+    if len(env.full_rodata):
+        log(LOG_LEVEL_1, 'rodata size:  {}'.format(len(env.full_rodata)))
+    log(LOG_LEVEL_1, 'bss size:     {}'.format(len(env.full_bss)))
+    log(LOG_LEVEL_1, 'GOT entries:  {}'.format(len(env.got_entries)))
+
+    #xxd(env.full_text)
+
+    out = MPYOutput()
+    out.open(fmpy)
+
+    # MPY: header
+    out.write_bytes(bytearray([
+        ord('M'),
+        MPY_VERSION,
+        env.arch.mpy_feature,
+        MP_SMALL_INT_BITS,
+        QSTR_WINDOW_SIZE,
+    ]))
+
+    # MPY: kind/len
+    out.write_uint(len(env.full_text) << 2 | (MP_CODE_NATIVE_VIPER - MP_CODE_BYTECODE))
+
+    # MPY: machine code
+    out.write_bytes(env.full_text)
+
+    # MPY: n_qstr_link (assumes little endian)
+    out.write_uint(len(native_qstr_vals) + len(native_qstr_objs))
+    for q in range(len(native_qstr_vals)):
+        off = env.qstr_val_section.addr + q * env.arch.qstr_entry_size
+        out.write_uint(off << 2)
+        out.write_qstr(native_qstr_vals[q])
+    for q in range(len(native_qstr_objs)):
+        off = env.qstr_obj_section.addr + q * env.arch.word_size
+        out.write_uint(off << 2 | 3)
+        out.write_qstr(native_qstr_objs[q])
+
+    # MPY: scope_flags
+    scope_flags = MP_SCOPE_FLAG_VIPERRELOC
+    if len(env.full_rodata):
+        scope_flags |= MP_SCOPE_FLAG_VIPERRODATA
+    if len(env.full_bss):
+        scope_flags |= MP_SCOPE_FLAG_VIPERBSS
+    out.write_uint(scope_flags)
+
+    # MPY: n_obj
+    out.write_uint(bool(len(env.full_rodata)) + bool(len(env.full_bss)))
+
+    # MPY: n_raw_code
+    out.write_uint(0)
+
+    # MPY: optional bytes object with rodata
+    if len(env.full_rodata):
+        out.write_obj(Ellipsis)
+    if len(env.full_bss):
+        out.write_obj(Ellipsis)
+
+    # MPY: rodata and/or bss
+    if len(env.full_rodata):
+        rodata_const_table_idx = 1
+        out.write_uint(len(env.full_rodata))
+        out.write_bytes(env.full_rodata)
+    if len(env.full_bss):
+        bss_const_table_idx = bool(env.full_rodata) + 1
+        out.write_uint(len(env.full_bss))
+
+    # MPY: relocation information
+    prev_kind = None
+    for base, addr, kind in env.mpy_relocs:
+        if isinstance(kind, str) and kind.startswith('.text'):
+            kind = 0
+        elif kind in ('.rodata', '.data.rel.ro'):
+            if env.arch.separate_rodata:
+                kind = rodata_const_table_idx
+            else:
+                kind = 0
+        elif isinstance(kind, str) and kind.startswith('.bss'):
+            kind = bss_const_table_idx
+        elif kind == 'mp_fun_table':
+            kind = 6
+        else:
+            kind = 7 + kind
+        assert addr % env.arch.word_size == 0, addr
+        offset = addr // env.arch.word_size
+        if kind == prev_kind and base == prev_base and offset == prev_offset + 1:
+            prev_n += 1
+            prev_offset += 1
+        else:
+            if prev_kind is not None:
+                out.write_reloc(prev_base, prev_offset - prev_n + 1, prev_kind, prev_n)
+            prev_kind = kind
+            prev_base = base
+            prev_offset = offset
+            prev_n = 1
+    if prev_kind is not None:
+        out.write_reloc(prev_base, prev_offset - prev_n + 1, prev_kind, prev_n)
+
+    # MPY: sentinel for end of relocations
+    out.write_bytes(b'\xff')
+
+    out.close()
+
+################################################################################
+# main
+
+def do_preprocess(args):
+    if args.output is None:
+        assert args.files[0].endswith('.c')
+        args.output = args.files[0][:-1] + 'config.h'
+    static_qstrs, qstr_vals, qstr_objs = extract_qstrs(args.files)
+    with open(args.output, 'w') as f:
+        print('#include <stdint.h>\n'
+            'typedef uintptr_t mp_uint_t;\n'
+            'typedef intptr_t mp_int_t;\n'
+            'typedef uintptr_t mp_off_t;', file=f)
+        for i, q in enumerate(static_qstrs):
+            print('#define %s (%u)' % (q, i + 1), file=f)
+        for i, q in enumerate(sorted(qstr_vals)):
+            print('#define %s (mp_native_qstr_val_table[%d])' % (q, i), file=f)
+        for i, q in enumerate(sorted(qstr_objs)):
+            print('#define MP_OBJ_NEW_QSTR_%s ((mp_obj_t)mp_native_qstr_obj_table[%d])' % (q, i), file=f)
+        if args.arch == 'xtensawin':
+            qstr_type = 'uint32_t' # esp32 can only read 32-bit values from IRAM
+        else:
+            qstr_type = 'uint16_t'
+        print('extern const {} mp_native_qstr_val_table[];'.format(qstr_type), file=f)
+        print('extern const mp_uint_t mp_native_qstr_obj_table[];', file=f)
+
+def do_link(args):
+    if args.output is None:
+        assert args.files[0].endswith('.o')
+        args.output = args.files[0][:-1] + 'mpy'
+    native_qstr_vals = []
+    native_qstr_objs = []
+    if args.qstrs is not None:
+        with open(args.qstrs) as f:
+            for l in f:
+                m = re.match(r'#define MP_QSTR_([A-Za-z0-9_]*) \(mp_native_', l)
+                if m:
+                    native_qstr_vals.append(m.group(1))
+                else:
+                    m = re.match(r'#define MP_OBJ_NEW_QSTR_MP_QSTR_([A-Za-z0-9_]*)', l)
+                    if m:
+                        native_qstr_objs.append(m.group(1))
+    log(LOG_LEVEL_2, 'qstr vals: ' + ', '.join(native_qstr_vals))
+    log(LOG_LEVEL_2, 'qstr objs: ' + ', '.join(native_qstr_objs))
+    env = LinkEnv(args.arch)
+    try:
+        for file in args.files:
+            load_object_file(env, file)
+        link_objects(env, len(native_qstr_vals), len(native_qstr_objs))
+        build_mpy(env, env.find_addr('mpy_init'), args.output, native_qstr_vals, native_qstr_objs)
+    except LinkError as er:
+        print('LinkError:', er.args[0])
+        sys.exit(1)
+
+def main():
+    import argparse
+    cmd_parser = argparse.ArgumentParser(description='Run scripts on the pyboard.')
+    cmd_parser.add_argument('--verbose', '-v', action='count', default=1, help='increase verbosity')
+    cmd_parser.add_argument('--arch', default='x64', help='architecture')
+    cmd_parser.add_argument('--preprocess', action='store_true', help='preprocess source files')
+    cmd_parser.add_argument('--qstrs', default=None, help='file defining additional qstrs')
+    cmd_parser.add_argument('--output', '-o', default=None, help='output .mpy file (default to input with .o->.mpy)')
+    cmd_parser.add_argument('files', nargs='+', help='input files')
+    args = cmd_parser.parse_args()
+
+    global log_level
+    log_level = args.verbose
+
+    if args.preprocess:
+        do_preprocess(args)
+    else:
+        do_link(args)
+
+if __name__ == '__main__':
+    main()