emscripten.py

# Copyright 2010 The Emscripten Authors.  All rights reserved.
# Emscripten is available under two separate licenses, the MIT license and the
# University of Illinois/NCSA Open Source License.  Both these licenses can be
# found in the LICENSE file.

"""A small wrapper script around the core JS compiler. This calls that
compiler with the settings given to it. It can also read data from C/C++
header files (so that the JS compiler can see the constants in those
headers, for the libc implementation in JS).
"""

from tools.toolchain_profiler import ToolchainProfiler

import os
import json
import subprocess
import time
import logging
import pprint
import shutil
import sys

from tools import building
from tools import diagnostics
from tools import js_manipulation
from tools import shared
from tools import utils
from tools import webassembly
from tools import extract_metadata
from tools.utils import exit_with_error, path_from_root, removeprefix
from tools.shared import DEBUG, asmjs_mangle
from tools.shared import treat_as_user_export
from tools.settings import settings

sys.path.append(path_from_root('third_party'))
import leb128

logger = logging.getLogger('emscripten')


def compute_minimal_runtime_initializer_and_exports(post, exports, receiving):
  # Declare all exports out to global JS scope so that JS library functions can access them in a
  # way that minifies well with Closure
  # e.g. var a,b,c,d,e,f;
  exports_that_are_not_initializers = [x for x in exports if x not in building.WASM_CALL_CTORS]
  # In Wasm backend the exports are still unmangled at this point, so mangle the names here
  exports_that_are_not_initializers = [asmjs_mangle(x) for x in exports_that_are_not_initializers]

  # Decide whether we should generate the global dynCalls dictionary for the dynCall() function?
  if settings.DYNCALLS and '$dynCall' in settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE and len([x for x in exports_that_are_not_initializers if x.startswith('dynCall_')]) > 0:
    exports_that_are_not_initializers += ['dynCalls = {}']

  declares = 'var ' + ',\n '.join(exports_that_are_not_initializers) + ';'
  post = shared.do_replace(post, '<<< WASM_MODULE_EXPORTS_DECLARES >>>', declares)

  # Generate assignments from all wasm exports out to the JS variables above: e.g. a = wasmExports['a']; b = wasmExports['b'];
  post = shared.do_replace(post, '<<< WASM_MODULE_EXPORTS >>>', receiving)
  return post


def write_output_file(outfile, module):
  for chunk in module:
    outfile.write(chunk)


def maybe_disable_filesystem(imports):
  """Disables filesystem if only a limited subset of syscalls is used.

  Our syscalls are static, and so if we see a very limited set of them - in particular,
  no open() syscall and just simple writing - then we don't need full filesystem support.
  If FORCE_FILESYSTEM is set, we can't do this. We also don't do it if INCLUDE_FULL_LIBRARY, since
  not including the filesystem would mean not including the full JS libraries, and the same for
  MAIN_MODULE=1 since a side module might need the filesystem.
  """
  if any(settings[s] for s in ['FORCE_FILESYSTEM', 'INCLUDE_FULL_LIBRARY']):
    return
  if settings.MAIN_MODULE == 1:
    return

  if settings.FILESYSTEM == 0:
    # without filesystem support, it doesn't matter what syscalls need
    settings.SYSCALLS_REQUIRE_FILESYSTEM = 0
  else:
    # TODO(sbc): Find a better way to identify wasi syscalls
    syscall_prefixes = ('__syscall_', 'fd_')
    side_module_imports = [shared.demangle_c_symbol_name(s) for s in settings.SIDE_MODULE_IMPORTS]
    all_imports = set(imports).union(side_module_imports)
    syscalls = {d for d in all_imports if d.startswith(syscall_prefixes) or d in ['path_open']}
    # check if the only filesystem syscalls are in: close, ioctl, llseek, write
    # (without open, etc.. nothing substantial can be done, so we can disable
    # extra filesystem support in that case)
    if syscalls.issubset({
      '__syscall_ioctl',
      'fd_seek',
      'fd_write',
      'fd_close',
      'fd_fdstat_get',
    }):
      if DEBUG:
        logger.debug('very limited syscalls (%s) so disabling full filesystem support', ', '.join(str(s) for s in syscalls))
      settings.SYSCALLS_REQUIRE_FILESYSTEM = 0


def is_int(x):
  try:
    int(x)
    return True
  except ValueError:
    return False


def align_memory(addr):
  return (addr + 15) & -16


def update_settings_glue(wasm_file, metadata):
  maybe_disable_filesystem(metadata.imports)

  # Integrate info from backend
  if settings.SIDE_MODULE:
    # we don't need any JS library contents in side modules
    settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE = []
  else:
    syms = settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE + metadata.imports
    syms = set(syms).difference(metadata.all_exports)
    settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE = sorted(syms)
    if settings.MAIN_MODULE:
      settings.WEAK_IMPORTS += webassembly.get_weak_imports(wasm_file)

  settings.WASM_EXPORTS = metadata.all_exports
  settings.WASM_GLOBAL_EXPORTS = list(metadata.namedGlobals.keys())
  settings.HAVE_EM_ASM = bool(settings.MAIN_MODULE or len(metadata.asmConsts) != 0)

  # start with the MVP features, and add any detected features.
  settings.BINARYEN_FEATURES = ['--mvp-features'] + metadata.features
  if settings.ASYNCIFY == 2:
    settings.BINARYEN_FEATURES += ['--enable-reference-types']

  if settings.PTHREADS:
    assert '--enable-threads' in settings.BINARYEN_FEATURES
  if settings.MEMORY64:
    assert '--enable-memory64' in settings.BINARYEN_FEATURES

  settings.HAS_MAIN = bool(settings.MAIN_MODULE) or settings.PROXY_TO_PTHREAD or settings.STANDALONE_WASM or 'main' in settings.WASM_EXPORTS or '__main_argc_argv' in settings.WASM_EXPORTS
  if settings.HAS_MAIN and not settings.MINIMAL_RUNTIME:
    # Dependencies of `callMain`
    settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE += ['$exitJS', '$handleException']

  # When using dynamic linking the main function might be in a side module.
  # To be safe assume they do take input parametes.
  settings.MAIN_READS_PARAMS = metadata.mainReadsParams or bool(settings.MAIN_MODULE)
  if settings.MAIN_READS_PARAMS and not settings.STANDALONE_WASM:
    # callMain depends on this library function
    settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE += ['$stringToUTF8OnStack']

  if settings.STACK_OVERFLOW_CHECK and not settings.SIDE_MODULE:
    # writeStackCookie and checkStackCookie both rely on emscripten_stack_get_end being
    # exported.  In theory it should always be present since its defined in compiler-rt.
    assert 'emscripten_stack_get_end' in metadata.function_exports

  for deps in metadata.jsDeps:
    settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE.extend(deps.split(','))


def apply_static_code_hooks(forwarded_json, code):
  code = shared.do_replace(code, '<<< ATINITS >>>', str(forwarded_json['ATINITS']))
  if settings.HAS_MAIN:
    code = shared.do_replace(code, '<<< ATMAINS >>>', str(forwarded_json['ATMAINS']))
  if settings.EXIT_RUNTIME and (not settings.MINIMAL_RUNTIME or settings.HAS_MAIN):
    code = shared.do_replace(code, '<<< ATEXITS >>>', str(forwarded_json['ATEXITS']))
  return code


def compile_javascript(symbols_only=False):
  stderr_file = os.environ.get('EMCC_STDERR_FILE')
  if stderr_file:
    stderr_file = os.path.abspath(stderr_file)
    logger.info('logging stderr in js compiler phase into %s' % stderr_file)
    stderr_file = open(stderr_file, 'w')

  # Save settings to a file to work around v8 issue 1579
  with shared.get_temp_files().get_file('.json') as settings_file:
    with open(settings_file, 'w') as s:
      json.dump(settings.external_dict(), s, sort_keys=True, indent=2)

    # Call js compiler
    env = os.environ.copy()
    env['EMCC_BUILD_DIR'] = os.getcwd()
    args = [settings_file]
    if symbols_only:
      args += ['--symbols-only']
    out = shared.run_js_tool(path_from_root('src/compiler.js'),
                             args, stdout=subprocess.PIPE, stderr=stderr_file,
                             cwd=path_from_root('src'), env=env, encoding='utf-8')
  if symbols_only:
    glue = None
    forwarded_data = out
  else:
    assert '//FORWARDED_DATA:' in out, 'Did not receive forwarded data in pre output - process failed?'
    glue, forwarded_data = out.split('//FORWARDED_DATA:')
  return glue, forwarded_data


def set_memory(static_bump):
  stack_low = align_memory(settings.GLOBAL_BASE + static_bump)
  stack_high = align_memory(stack_low + settings.STACK_SIZE)
  settings.STACK_HIGH = stack_high
  settings.STACK_LOW = stack_low
  settings.HEAP_BASE = align_memory(stack_high)


def report_missing_symbols(js_symbols):
  # Report any symbol that was explicitly exported but is present neither
  # as a native function nor as a JS library function.
  defined_symbols = set(asmjs_mangle(e) for e in settings.WASM_EXPORTS).union(js_symbols)
  missing = set(settings.USER_EXPORTED_FUNCTIONS) - defined_symbols
  for symbol in sorted(missing):
    diagnostics.warning('undefined', f'undefined exported symbol: "{symbol}"')

  # Special hanlding for the `_main` symbol

  if settings.STANDALONE_WASM:
    # standalone mode doesn't use main, and it always reports missing entry point at link time.
    # In this mode we never expect _main in the export list.
    return

  if settings.IGNORE_MISSING_MAIN:
    # The default mode for emscripten is to ignore the missing main function allowing
    # maximum compatibility.
    return

  if settings.EXPECT_MAIN and 'main' not in settings.WASM_EXPORTS and '__main_argc_argv' not in settings.WASM_EXPORTS:
    # For compatibility with the output of wasm-ld we use the same wording here in our
    # error message as if wasm-ld had failed.
    exit_with_error('entry symbol not defined (pass --no-entry to suppress): main')


# Test if the parentheses at body[openIdx] and body[closeIdx] are a match to
# each other.
def parentheses_match(body, openIdx, closeIdx):
  if closeIdx < 0:
    closeIdx += len(body)
  count = 1
  for i in range(openIdx + 1, closeIdx + 1):
    if body[i] == body[openIdx]:
      count += 1
    elif body[i] == body[closeIdx]:
      count -= 1
      if count <= 0:
        return i == closeIdx
  return False


def trim_asm_const_body(body):
  body = body.strip()
  orig = None
  while orig != body:
    orig = body
    if len(body) > 1 and body[0] == '"' and body[-1] == '"':
      body = body[1:-1].replace('\\"', '"').strip()
    if len(body) > 1 and body[0] == '{' and body[-1] == '}' and parentheses_match(body, 0, -1):
      body = body[1:-1].strip()
    if len(body) > 1 and body[0] == '(' and body[-1] == ')' and parentheses_match(body, 0, -1):
      body = body[1:-1].strip()
  return body


def create_named_globals(metadata):
  named_globals = []
  for k, v in metadata.namedGlobals.items():
    v = int(v)
    if settings.RELOCATABLE:
      v += settings.GLOBAL_BASE
    mangled = asmjs_mangle(k)
    if settings.MINIMAL_RUNTIME:
      named_globals.append("var %s = %s;" % (mangled, v))
    else:
      named_globals.append("var %s = Module['%s'] = %s;" % (mangled, mangled, v))

  return '\n'.join(named_globals)


def emscript(in_wasm, out_wasm, outfile_js, memfile, js_syms):
  # Overview:
  #   * Run wasm-emscripten-finalize to extract metadata and modify the binary
  #     to use emscripten's wasm<->JS ABI
  #   * Use the metadata to generate the JS glue that goes with the wasm

  if settings.SINGLE_FILE:
    # placeholder strings for JS glue, to be replaced with subresource locations in do_binaryen
    settings.WASM_BINARY_FILE = '<<< WASM_BINARY_FILE >>>'
  else:
    # set file locations, so that JS glue can find what it needs
    settings.WASM_BINARY_FILE = js_manipulation.escape_for_js_string(os.path.basename(out_wasm))

  metadata = finalize_wasm(in_wasm, out_wasm, memfile, js_syms)

  if settings.RELOCATABLE and settings.MEMORY64 == 2:
    metadata.imports += ['__memory_base32']

  if settings.ASYNCIFY == 1:
    metadata.function_exports['asyncify_start_unwind'] = 1
    metadata.function_exports['asyncify_stop_unwind'] = 0
    metadata.function_exports['asyncify_start_rewind'] = 1
    metadata.function_exports['asyncify_stop_rewind'] = 0

  update_settings_glue(out_wasm, metadata)

  if not settings.WASM_BIGINT and metadata.emJsFuncs:
    import_map = {}

    with webassembly.Module(in_wasm) as module:
      types = module.get_types()
      for imp in module.get_imports():
        if imp.module not in ('GOT.mem', 'GOT.func'):
          import_map[imp.field] = imp

    for em_js_func, raw in metadata.emJsFuncs.items():
      c_sig = raw.split('<::>')[0].strip('()')
      if not c_sig or c_sig == 'void':
        c_sig = []
      else:
        c_sig = c_sig.split(',')
      if em_js_func in import_map:
        imp = import_map[em_js_func]
        assert imp.kind == webassembly.ExternType.FUNC
        signature = types[imp.type]
        if len(signature.params) != len(c_sig):
          diagnostics.warning('em-js-i64', 'using 64-bit arguments in EM_JS function without WASM_BIGINT is not yet fully supported: `%s` (%s, %s)', em_js_func, c_sig, signature.params)

  if settings.SIDE_MODULE:
    logger.debug('emscript: skipping remaining js glue generation')
    return

  if DEBUG:
    logger.debug('emscript: js compiler glue')
    t = time.time()

  # memory and global initializers

  if settings.RELOCATABLE:
    dylink_sec = webassembly.parse_dylink_section(in_wasm)
    static_bump = align_memory(dylink_sec.mem_size)
    set_memory(static_bump)
    logger.debug('stack_low: %d, stack_high: %d, heap_base: %d', settings.STACK_LOW, settings.STACK_HIGH, settings.HEAP_BASE)

    # When building relocatable output (e.g. MAIN_MODULE) the reported table
    # size does not include the reserved slot at zero for the null pointer.
    # So we need to offset the elements by 1.
    if settings.INITIAL_TABLE == -1:
      settings.INITIAL_TABLE = dylink_sec.table_size + 1

    if settings.ASYNCIFY == 1:
      metadata.imports += ['__asyncify_state', '__asyncify_data']

  if metadata.invokeFuncs:
    settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE += ['$getWasmTableEntry']

  glue, forwarded_data = compile_javascript()
  if DEBUG:
    logger.debug('  emscript: glue took %s seconds' % (time.time() - t))
    t = time.time()

  forwarded_json = json.loads(forwarded_data)

  if forwarded_json['warnings']:
    diagnostics.warning('js-compiler', 'warnings in JS library compilation')

  pre, post = glue.split('// EMSCRIPTEN_END_FUNCS')

  if settings.ASSERTIONS:
    pre += "function checkIncomingModuleAPI() {\n"
    for sym in settings.ALL_INCOMING_MODULE_JS_API:
      if sym not in settings.INCOMING_MODULE_JS_API:
        pre += f"  ignoredModuleProp('{sym}');\n"
    pre += "}\n"

  report_missing_symbols(forwarded_json['librarySymbols'])

  if not outfile_js:
    logger.debug('emscript: skipping remaining js glue generation')
    return

  if settings.MINIMAL_RUNTIME:
    # In MINIMAL_RUNTIME, atinit exists in the postamble part
    post = apply_static_code_hooks(forwarded_json, post)
  else:
    # In regular runtime, atinits etc. exist in the preamble part
    pre = apply_static_code_hooks(forwarded_json, pre)

  asm_consts = create_asm_consts(metadata)
  em_js_funcs = create_em_js(metadata)
  asm_const_pairs = ['%s: %s' % (key, value) for key, value in asm_consts]
  extra_code = ''
  if asm_const_pairs or settings.MAIN_MODULE:
    extra_code += 'var ASM_CONSTS = {\n  ' + ',  \n '.join(asm_const_pairs) + '\n};\n'
  if em_js_funcs:
    extra_code += '\n'.join(em_js_funcs) + '\n'
  if extra_code:
    pre = pre.replace(
      '// === Body ===\n',
      '// === Body ===\n\n' + extra_code + '\n')

  with open(outfile_js, 'w', encoding='utf-8') as out:
    out.write(pre)
    pre = None

    receiving = create_receiving(metadata.function_exports)

    if settings.MINIMAL_RUNTIME:
      if settings.DECLARE_ASM_MODULE_EXPORTS:
        post = compute_minimal_runtime_initializer_and_exports(post, metadata.function_exports, receiving)
      receiving = ''

    module = create_module(receiving, metadata, forwarded_json['librarySymbols'])

    write_output_file(out, module)

    out.write(post)
    module = None


def remove_trailing_zeros(memfile):
  mem_data = utils.read_binary(memfile)
  mem_data = mem_data.rstrip(b'\0')
  utils.write_binary(memfile, mem_data)


@ToolchainProfiler.profile()
def get_metadata(infile, outfile, modify_wasm, args):
  metadata = extract_metadata.extract_metadata(infile)
  if modify_wasm:
    # In some cases we still need to modify the wasm file
    # using wasm-emscripten-finalize.
    building.run_binaryen_command('wasm-emscripten-finalize',
                                  infile=infile,
                                  outfile=outfile,
                                  args=args)
    # When we do this we can generate new imports, so
    # re-read parts of the metadata post-finalize
    extract_metadata.update_metadata(outfile, metadata)
  if DEBUG:
    logger.debug("Metadata: " + pprint.pformat(metadata.__dict__))
  return metadata


def finalize_wasm(infile, outfile, memfile, js_syms):
  building.save_intermediate(infile, 'base.wasm')
  args = []

  # if we don't need to modify the wasm, don't tell finalize to emit a wasm file
  modify_wasm = False

  if settings.WASM2JS:
    # wasm2js requires full legalization (and will do extra wasm binary
    # later processing later anyhow)
    modify_wasm = True
  if settings.DEBUG_LEVEL >= 2 or settings.ASYNCIFY_ADD or settings.ASYNCIFY_ADVISE or settings.ASYNCIFY_ONLY or settings.ASYNCIFY_REMOVE or settings.EMIT_SYMBOL_MAP or settings.EMIT_NAME_SECTION:
    args.append('-g')
  if settings.WASM_BIGINT:
    args.append('--bigint')
  if settings.DYNCALLS:
    # we need to add all dyncalls to the wasm
    modify_wasm = True
  else:
    if settings.WASM_BIGINT:
      args.append('--no-dyncalls')
    else:
      args.append('--dyncalls-i64')
      # we need to add some dyncalls to the wasm
      modify_wasm = True
  if settings.AUTODEBUG:
    # In AUTODEBUG mode we want to delay all legalization until later.  This is hack
    # to force wasm-emscripten-finalize not to do any legalization at all.
    args.append('--bigint')
  else:
    if settings.LEGALIZE_JS_FFI:
      # When we dynamically link our JS loader adds functions from wasm modules to
      # the table. It must add the original versions of them, not legalized ones,
      # so that indirect calls have the right type, so export those.
      args += building.js_legalization_pass_flags()
      modify_wasm = True
    else:
      args.append('--no-legalize-javascript-ffi')
  if memfile:
    args.append(f'--separate-data-segments={memfile}')
    args.append(f'--global-base={settings.GLOBAL_BASE}')
    modify_wasm = True
  if settings.SIDE_MODULE:
    args.append('--side-module')
  if settings.STACK_OVERFLOW_CHECK >= 2:
    args.append('--check-stack-overflow')
    modify_wasm = True
  if settings.STANDALONE_WASM:
    args.append('--standalone-wasm')

  if settings.DEBUG_LEVEL >= 3:
    args.append('--dwarf')

  if infile != outfile:
    shutil.copy(infile, outfile)

  if settings.GENERATE_SOURCE_MAP:
    building.emit_wasm_source_map(infile, outfile + '.map', outfile)
    building.save_intermediate(outfile + '.map', 'base_wasm.map')
    base_url = settings.SOURCE_MAP_BASE + os.path.basename(outfile) + '.map'
    if modify_wasm:
      # If we are already modifying, just let Binaryen add the sourcemap URL
      args += ['--output-source-map-url=' + base_url]
    else:
      # Otherwise use objcopy. This avoids re-encoding the file (thus
      # preserving DWARF) and is faster.

      # Create a file with the contents of the sourceMappingURL section
      with shared.get_temp_files().get_file('.bin') as url_file:
        utils.write_binary(url_file,
                           leb128.u.encode(len(base_url)) + base_url.encode('utf-8'))
        cmd = [shared.LLVM_OBJCOPY,
               '--add-section',
               'sourceMappingURL=' + url_file,
               infile]
        shared.check_call(cmd)

  if not settings.GENERATE_DWARF or not settings.EMIT_PRODUCERS_SECTION:
    # For sections we no longer need, strip now to speed subsequent passes
    building.save_intermediate(outfile, 'strip.wasm')
    sections = ['producers'] if not settings.EMIT_PRODUCERS_SECTION else []
    building.strip(infile, outfile, debug=not settings.GENERATE_DWARF,
                   sections=sections)

  metadata = get_metadata(outfile, outfile, modify_wasm, args)
  if modify_wasm:
    building.save_intermediate(outfile, 'post_finalize.wasm')

  if settings.GENERATE_SOURCE_MAP:
    building.save_intermediate(outfile + '.map', 'post_finalize.map')

  if memfile:
    # we have a separate .mem file. binaryen did not strip any trailing zeros,
    # because it's an ABI question as to whether it is valid to do so or not.
    # we can do so here, since we make sure to zero out that memory (even in
    # the dynamic linking case, our loader zeros it out)
    remove_trailing_zeros(memfile)

  expected_exports = set(settings.EXPORTED_FUNCTIONS)
  expected_exports.update(asmjs_mangle(s) for s in settings.REQUIRED_EXPORTS)
  # Assume that when JS symbol dependencies are exported it is because they
  # are needed by by a JS symbol and are not being explicitly exported due
  # to EMSCRIPTEN_KEEPALIVE (llvm.used).
  for deps in js_syms.values():
    expected_exports.update(asmjs_mangle(s) for s in deps)

  # Calculate the subset of exports that were explicitly marked as
  # EMSCRIPTEN_KEEPALIVE (llvm.used).
  # These are any exports that were not requested on the command line and are
  # not known auto-generated system functions.
  unexpected_exports = [e for e in metadata.all_exports if treat_as_user_export(e)]
  unexpected_exports = [asmjs_mangle(e) for e in unexpected_exports]
  unexpected_exports = [e for e in unexpected_exports if e not in expected_exports]
  if '_main' in unexpected_exports:
    logger.warning('main() is in the input files, but "_main" is not in EXPORTED_FUNCTIONS, which means it may be eliminated as dead code. Export it if you want main() to run.')
    unexpected_exports.remove('_main')

  building.user_requested_exports.update(unexpected_exports)
  settings.EXPORTED_FUNCTIONS.extend(unexpected_exports)

  return metadata


def create_asm_consts(metadata):
  asm_consts = {}
  for addr, const in metadata.asmConsts.items():
    body = trim_asm_const_body(const)
    args = []
    max_arity = 16
    arity = 0
    for i in range(max_arity):
      if ('$' + str(i)) in const:
        arity = i + 1
    for i in range(arity):
      args.append('$' + str(i))
    args = ', '.join(args)
    if 'arguments' in body:
      # arrow functions don't bind `arguments` so we have to use
      # the old function syntax in this case
      func = f'function({args}) {{ {body} }}'
    else:
      func = f'({args}) => {{ {body} }}'
    if settings.RELOCATABLE:
      addr += settings.GLOBAL_BASE
    asm_consts[addr] = func
  asm_consts = [(key, value) for key, value in asm_consts.items()]
  asm_consts.sort()
  return asm_consts


def type_to_sig(type):
  # These should match the conversion in $sigToWasmTypes.
  return {
    webassembly.Type.I32: 'i',
    webassembly.Type.I64: 'j',
    webassembly.Type.F32: 'f',
    webassembly.Type.F64: 'd',
    webassembly.Type.VOID: 'v'
  }[type]


def func_type_to_sig(type):
  parameters = [type_to_sig(param) for param in type.params]
  if type.returns:
    assert len(type.returns) == 1, "One return type expected."
    ret = type.returns[0]
  else:
    ret = webassembly.Type.VOID
  return type_to_sig(ret) + ''.join(parameters)


def create_em_js(metadata):
  em_js_funcs = []
  separator = '<::>'
  for name, raw in metadata.emJsFuncs.items():
    assert separator in raw
    args, body = raw.split(separator, 1)
    args = args[1:-1]
    if args == 'void':
      args = []
    else:
      args = args.split(',')
    arg_names = [arg.split()[-1].replace('*', '') for arg in args if arg]
    args = ','.join(arg_names)
    func = f'function {name}({args}) {body}'
    if (settings.MAIN_MODULE or settings.ASYNCIFY == 2) and name in metadata.emJsFuncTypes:
      sig = func_type_to_sig(metadata.emJsFuncTypes[name])
      func = func + f'\n{name}.sig = \'{sig}\';'
    em_js_funcs.append(func)

  return em_js_funcs


def add_standard_wasm_imports(send_items_map):
  extra_sent_items = []

  if settings.IMPORTED_MEMORY:
    memory_import = 'wasmMemory'
    if settings.MODULARIZE and settings.PTHREADS:
      # Pthreads assign wasmMemory in their worker startup. In MODULARIZE mode, they cannot assign inside the
      # Module scope, so lookup via Module as well.
      memory_import += " || Module['wasmMemory']"
    send_items_map['memory'] = memory_import

  if settings.SAFE_HEAP:
    extra_sent_items.append('segfault')
    extra_sent_items.append('alignfault')

  if settings.RELOCATABLE:
    send_items_map['__indirect_function_table'] = 'wasmTable'

  if settings.AUTODEBUG:
    extra_sent_items += [
      'log_execution',
      'get_i32',
      'get_i64',
      'get_f32',
      'get_f64',
      'get_anyref',
      'get_exnref',
      'set_i32',
      'set_i64',
      'set_f32',
      'set_f64',
      'set_anyref',
      'set_exnref',
      'load_ptr',
      'load_val_i32',
      'load_val_i64',
      'load_val_f32',
      'load_val_f64',
      'store_ptr',
      'store_val_i32',
      'store_val_i64',
      'store_val_f32',
      'store_val_f64',
    ]

  if settings.SPLIT_MODULE and settings.ASYNCIFY == 2:
    # Calls to this function are generated by binaryen so it must be manually
    # imported.
    extra_sent_items.append('__load_secondary_module')

  for s in extra_sent_items:
    send_items_map[s] = s


def create_sending(metadata, library_symbols):
  # Map of wasm imports to mangled/external/JS names
  send_items_map = {}

  for name in metadata.invokeFuncs:
    send_items_map[name] = name
  for name in metadata.imports:
    if name in metadata.emJsFuncs:
      send_items_map[name] = name
    else:
      send_items_map[name] = asmjs_mangle(name)

  add_standard_wasm_imports(send_items_map)

  if settings.MAIN_MODULE:
    # When including dynamic linking support, also add any JS library functions
    # that are part of EXPORTED_FUNCTIONS (or in the case of MAIN_MODULE=1 add
    # all JS library functions).  This allows `dlsym(RTLD_DEFAULT)` to lookup JS
    # library functions, since `wasmImports` acts as the global symbol table.
    wasm_exports = set(metadata.function_exports)
    library_symbols = set(library_symbols)
    if settings.MAIN_MODULE == 1:
      for f in library_symbols:
        if shared.is_c_symbol(f):
          demangled = shared.demangle_c_symbol_name(f)
          if demangled in wasm_exports:
            continue
          send_items_map[demangled] = f
    else:
      for f in settings.EXPORTED_FUNCTIONS + settings.SIDE_MODULE_IMPORTS:
        if f in library_symbols and shared.is_c_symbol(f):
          demangled = shared.demangle_c_symbol_name(f)
          if demangled in wasm_exports:
            continue
          send_items_map[demangled] = f

  sorted_items = sorted(send_items_map.items())
  prefix = ''
  if settings.MAYBE_CLOSURE_COMPILER:
    # This prevents closure compiler from minifying the field names in this
    # object.
    prefix = '/** @export */\n  '
  return '{\n  ' + ',\n  '.join(f'{prefix}{k}: {v}' for k, v in sorted_items) + '\n}'


def make_export_wrappers(function_exports, delay_assignment):
  wrappers = []

  # The emscripten stack functions are called very early (by writeStackCookie) before
  # the runtime is initialized so we can't create these wrappers that check for
  # runtimeInitialized.
  # Likewise `__trap` can occur before the runtime is initialized since it is used in
  # abort.
  # pthread_self and _emscripten_proxy_execute_task_queue are currently called in some
  # cases after the runtime has exited.
  # TODO: Look into removing these, and improving our robustness around thread termination.
  def install_wrapper(sym):
    if sym.startswith('_asan_') or sym.startswith('emscripten_stack_'):
      return False
    if sym in ('__trap', 'pthread_self', '_emscripten_proxy_execute_task_queue'):
      return False
    return True

  for name, nargs in function_exports.items():
    mangled = asmjs_mangle(name)
    wrapper = 'var %s = ' % mangled

    # TODO(sbc): Can we avoid exporting the dynCall_ functions on the module.
    should_export = settings.EXPORT_KEEPALIVE and mangled in settings.EXPORTED_FUNCTIONS
    if name.startswith('dynCall_') or should_export:
      exported = "Module['%s'] = " % mangled
    else:
      exported = ''
    wrapper += exported

    if settings.ASSERTIONS and install_wrapper(name):
      # With assertions enabled we create a wrapper that are calls get routed through, for
      # the lifetime of the program.
      wrapper += "createExportWrapper('%s');" % name
    elif delay_assignment:
      # With assertions disabled the wrapper will replace the global var and Module var on
      # first use.
      args = [f'a{i}' for i in range(nargs)]
      args = ', '.join(args)
      wrapper += f"({args}) => ({mangled} = {exported}wasmExports['{name}'])({args});"
    else:
      wrapper += 'wasmExports["%s"]' % name

    wrappers.append(wrapper)
  return wrappers


def create_receiving(function_exports):
  # When not declaring asm exports this section is empty and we instead programatically export
  # symbols on the global object by calling exportWasmSymbols after initialization
  if not settings.DECLARE_ASM_MODULE_EXPORTS:
    return ''

  receiving = []

  # with WASM_ASYNC_COMPILATION that asm object may not exist at this point in time
  # so we need to support delayed assignment.
  delay_assignment = settings.WASM_ASYNC_COMPILATION and not settings.MINIMAL_RUNTIME
  if not delay_assignment:
    if settings.MINIMAL_RUNTIME:
      # In Wasm exports are assigned inside a function to variables
      # existing in top level JS scope, i.e.
      # var _main;
      # WebAssembly.instantiate(Module['wasm'], imports).then((output) => {
      #   var wasmExports = output.instance.exports;
      #   _main = wasmExports["_main"];
      generate_dyncall_assignment = settings.DYNCALLS and '$dynCall' in settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE
      exports_that_are_not_initializers = [x for x in function_exports if x != building.WASM_CALL_CTORS]

      for s in exports_that_are_not_initializers:
        mangled = asmjs_mangle(s)
        dynCallAssignment = ('dynCalls["' + s.replace('dynCall_', '') + '"] = ') if generate_dyncall_assignment and mangled.startswith('dynCall_') else ''
        should_export = settings.EXPORT_ALL or (settings.EXPORT_KEEPALIVE and mangled in settings.EXPORTED_FUNCTIONS)
        export_assignment = ''
        if settings.MODULARIZE and should_export:
          export_assignment = f"Module['{mangled}'] = "
        receiving += [f'{export_assignment}{dynCallAssignment}{mangled} = wasmExports["{s}"]']
    else:
      receiving += make_export_wrappers(function_exports, delay_assignment)
  else:
    receiving += make_export_wrappers(function_exports, delay_assignment)

  if settings.MINIMAL_RUNTIME:
    return '\n  '.join(receiving) + '\n'
  else:
    return '\n'.join(receiving) + '\n'


def create_module(receiving, metadata, library_symbols):
  receiving += create_named_globals(metadata)
  module = []

  sending = create_sending(metadata, library_symbols)
  module.append('var wasmImports = %s;\n' % sending)
  if settings.ASYNCIFY and (settings.ASSERTIONS or settings.ASYNCIFY == 2):
    # instrumenting imports is used in asyncify in two ways: to add assertions
    # that check for proper import use, and for ASYNCIFY=2 we use them to set up
    # the Promise API on the import side.
    module.append('Asyncify.instrumentWasmImports(wasmImports);\n')

  if not settings.MINIMAL_RUNTIME:
    module.append("var wasmExports = createWasm();\n")

  module.append(receiving)
  if settings.SUPPORT_LONGJMP == 'emscripten' or not settings.DISABLE_EXCEPTION_CATCHING:
    module.append(create_invoke_wrappers(metadata))
  else:
    assert not metadata.invokeFuncs, "invoke_ functions exported but exceptions and longjmp are both disabled"
  if settings.MEMORY64 or settings.CAN_ADDRESS_2GB:
    module.append(create_pointer_conversion_wrappers(metadata))
  return module


def create_invoke_wrappers(metadata):
  """Asm.js-style exception handling: invoke wrapper generation."""
  invoke_wrappers = ''
  for invoke in metadata.invokeFuncs:
    sig = removeprefix(invoke, 'invoke_')
    invoke_wrappers += '\n' + js_manipulation.make_invoke(sig) + '\n'
  return invoke_wrappers


def create_pointer_conversion_wrappers(metadata):
  # TODO(sbc): Move this into somewhere less static.  Maybe it can become
  # part of library.js file, even though this metadata relates specifically
  # to native (non-JS) functions.
  #
  # The signature format here is similar to the one used for JS libraries
  # but with the following as the only valid char:
  #  '_' - non-pointer argument (pass through unchanged)
  #  'p' - pointer/int53 argument (convert to/from BigInt)
  #  'P' - same as above but allow `undefined` too (requires extra check)
  mapping = {
    'sbrk': 'pP',
    'stackAlloc': 'pp',
    'emscripten_builtin_malloc': 'pp',
    'malloc': 'pp',
    '__getTypeName': 'pp',
    'setThrew': '_p',
    'free': '_p',
    'stackRestore': '_p',
    '__cxa_is_pointer_type': '_p',
    'stackSave': 'p',
    'fflush': '_p',
    'emscripten_stack_get_end': 'p',
    'emscripten_stack_get_base': 'p',
    'pthread_self': 'p',
    'emscripten_stack_get_current': 'p',
    '__errno_location': 'p',
    'emscripten_builtin_memalign': 'ppp',
    'emscripten_builtin_free': 'vp',
    'main': '__PP',
    '__main_argc_argv': '__PP',
    'emscripten_stack_set_limits': '_pp',
    '__set_stack_limits': '_pp',
    '__cxa_can_catch': '_ppp',
    '__cxa_increment_exception_refcount': '_p',
    '__cxa_decrement_exception_refcount': '_p',
    '_wasmfs_write_file': '_ppp',
    '__dl_seterr': '_pp',
    '_emscripten_run_on_main_thread_js': '___p_',
    '_emscripten_proxy_execute_task_queue': '_p',
    '_emscripten_thread_exit': '_p',
    '_emscripten_thread_init': '_p_____',
    '_emscripten_thread_free_data': '_p',
    '_emscripten_dlsync_self_async': '_p',
    '_emscripten_proxy_dlsync_async': '_pp',
    '_wasmfs_rmdir': '_p',
    '_wasmfs_unlink': '_p',
    '_wasmfs_mkdir': '_p_',
    '_wasmfs_open': '_p__',
    'emscripten_wasm_worker_initialize': '_p_',
    'asyncify_start_rewind': '_p',
    'asyncify_start_unwind': '_p',
    '__get_exception_message': '_ppp',
  }

  for function in settings.SIGNATURE_CONVERSIONS:
    sym, sig = function.split(':')
    mapping[sym] = sig

  wrappers = '''
// Argument name here must shadow the `wasmExports` global so
// that it is recognised by metadce and minify-import-export-names
// passes.
function applySignatureConversions(wasmExports) {
  // First, make a copy of the incoming exports object
  wasmExports = Object.assign({}, wasmExports);
'''

  sigs_seen = set()
  wrap_functions = []
  for symbol in metadata.function_exports:
    sig = mapping.get(symbol)
    if sig:
      if settings.MEMORY64:
        if sig not in sigs_seen:
          wrappers += js_manipulation.make_wasm64_wrapper(sig)
          sigs_seen.add(sig)
        wrap_functions.append(symbol)
      elif sig[0] == 'p':
        if sig not in sigs_seen:
          wrappers += js_manipulation.make_unsign_pointer_wrapper(sig)
          sigs_seen.add(sig)
        wrap_functions.append(symbol)

  for f in wrap_functions:
    sig = mapping[f]
    wrappers += f"\n  wasmExports['{f}'] = makeWrapper_{sig}(wasmExports['{f}']);"
  wrappers += 'return wasmExports;\n}'

  return wrappers


def run(in_wasm, out_wasm, outfile_js, memfile, js_syms):
  emscript(in_wasm, out_wasm, outfile_js, memfile, js_syms)