tools/building.py

# Copyright 2020 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.

from .toolchain_profiler import ToolchainProfiler

import json
import logging
import os
import re
import shlex
import shutil
import subprocess
import sys
from typing import Set, Dict
from subprocess import PIPE

from . import cache
from . import diagnostics
from . import response_file
from . import shared
from . import webassembly
from . import config
from . import utils
from .shared import CLANG_CC, CLANG_CXX
from .shared import LLVM_NM, EMCC, EMAR, EMXX, EMRANLIB, WASM_LD
from .shared import LLVM_OBJCOPY
from .shared import run_process, check_call, exit_with_error
from .shared import path_from_root
from .shared import asmjs_mangle, DEBUG
from .shared import LLVM_DWARFDUMP, demangle_c_symbol_name
from .shared import get_emscripten_temp_dir, exe_suffix, is_c_symbol
from .utils import WINDOWS
from .settings import settings
from .feature_matrix import UNSUPPORTED

logger = logging.getLogger('building')

#  Building
binaryen_checked = False
EXPECTED_BINARYEN_VERSION = 119

_is_ar_cache: Dict[str, bool] = {}
# the exports the user requested
user_requested_exports: Set[str] = set()


def get_building_env():
  cache.ensure()
  env = os.environ.copy()
  # point CC etc. to the em* tools.
  env['CC'] = EMCC
  env['CXX'] = EMXX
  env['AR'] = EMAR
  env['LD'] = EMCC
  env['NM'] = LLVM_NM
  env['LDSHARED'] = EMCC
  env['RANLIB'] = EMRANLIB
  env['EMSCRIPTEN_TOOLS'] = path_from_root('tools')
  env['HOST_CC'] = CLANG_CC
  env['HOST_CXX'] = CLANG_CXX
  env['HOST_CFLAGS'] = '-W' # if set to nothing, CFLAGS is used, which we don't want
  env['HOST_CXXFLAGS'] = '-W' # if set to nothing, CXXFLAGS is used, which we don't want
  env['PKG_CONFIG_LIBDIR'] = cache.get_sysroot_dir('local/lib/pkgconfig') + os.path.pathsep + cache.get_sysroot_dir('lib/pkgconfig')
  env['PKG_CONFIG_PATH'] = os.environ.get('EM_PKG_CONFIG_PATH', '')
  env['EMSCRIPTEN'] = path_from_root()
  env['PATH'] = cache.get_sysroot_dir('bin') + os.pathsep + env['PATH']
  env['ACLOCAL_PATH'] = cache.get_sysroot_dir('share/aclocal')
  env['CROSS_COMPILE'] = path_from_root('em') # produces /path/to/emscripten/em , which then can have 'cc', 'ar', etc appended to it
  return env


def llvm_backend_args():
  # disable slow and relatively unimportant optimization passes
  args = ['-combiner-global-alias-analysis=false']

  # asm.js-style exception handling
  if not settings.DISABLE_EXCEPTION_CATCHING:
    args += ['-enable-emscripten-cxx-exceptions']
  if settings.EXCEPTION_CATCHING_ALLOWED:
    # When 'main' has a non-standard signature, LLVM outlines its content out to
    # '__original_main'. So we add it to the allowed list as well.
    if 'main' in settings.EXCEPTION_CATCHING_ALLOWED:
      settings.EXCEPTION_CATCHING_ALLOWED += ['__original_main', '__main_argc_argv']
    allowed = ','.join(settings.EXCEPTION_CATCHING_ALLOWED)
    args += ['-emscripten-cxx-exceptions-allowed=' + allowed]

  # asm.js-style setjmp/longjmp handling
  if settings.SUPPORT_LONGJMP == 'emscripten':
    args += ['-enable-emscripten-sjlj']
  # setjmp/longjmp handling using Wasm EH
  elif settings.SUPPORT_LONGJMP == 'wasm':
    args += ['-wasm-enable-sjlj']

  # better (smaller, sometimes faster) codegen, see binaryen#1054
  # and https://bugs.llvm.org/show_bug.cgi?id=39488
  args += ['-disable-lsr']

  return args


@ToolchainProfiler.profile()
def link_to_object(args, target):
  link_lld(args + ['--relocatable'], target)


def side_module_external_deps(external_symbols):
  """Find the list of the external symbols that are needed by the
  linked side modules.
  """
  deps = set()
  for sym in settings.SIDE_MODULE_IMPORTS:
    sym = demangle_c_symbol_name(sym)
    if sym in external_symbols:
      deps = deps.union(external_symbols[sym])
  return sorted(list(deps))


def create_stub_object(external_symbols):
  """Create a stub object, based on the JS library symbols and their
  dependencies, that we can pass to wasm-ld.
  """
  stubfile = shared.get_temp_files().get('libemscripten_js_symbols.so').name
  stubs = ['#STUB']
  for name, deps in external_symbols.items():
    if not name.startswith('$'):
      stubs.append('%s: %s' % (name, ','.join(deps)))
  utils.write_file(stubfile, '\n'.join(stubs))
  return stubfile


def lld_flags_for_executable(external_symbols):
  cmd = []
  if external_symbols:
    if settings.INCLUDE_FULL_LIBRARY:
      # When INCLUDE_FULL_LIBRARY is set try to export every possible
      # native dependency of a JS function.
      all_deps = set()
      for deps in external_symbols.values():
        for dep in deps:
          if dep not in all_deps:
            cmd.append('--export-if-defined=' + dep)
          all_deps.add(dep)
    stub = create_stub_object(external_symbols)
    cmd.append(stub)

  if not settings.ERROR_ON_UNDEFINED_SYMBOLS:
    cmd.append('--import-undefined')

  if settings.IMPORTED_MEMORY:
    cmd.append('--import-memory')

  if settings.SHARED_MEMORY:
    cmd.append('--shared-memory')

  # wasm-ld can strip debug info for us. this strips both the Names
  # section and DWARF, so we can only use it when we don't need any of
  # those things.
  if settings.DEBUG_LEVEL < 2 and (not settings.EMIT_SYMBOL_MAP and
                                   not settings.EMIT_NAME_SECTION and
                                   not settings.ASYNCIFY):
    cmd.append('--strip-debug')

  if settings.LINKABLE:
    cmd.append('--export-dynamic')

  if settings.LTO and not settings.EXIT_RUNTIME:
    # The WebAssembly backend can generate new references to `__cxa_atexit` at
    # LTO time.  This `-u` flag forces the `__cxa_atexit` symbol to be
    # included at LTO time.  For other such symbols we exclude them from LTO
    # and always build them as normal object files, but that would inhibit the
    # LowerGlobalDtors optimization which allows destructors to be completely
    # removed when __cxa_atexit is a no-op.
    cmd.append('-u__cxa_atexit')

  c_exports = [e for e in settings.EXPORTED_FUNCTIONS if is_c_symbol(e)]
  # Strip the leading underscores
  c_exports = [demangle_c_symbol_name(e) for e in c_exports]
  # Filter out symbols external/JS symbols
  c_exports = [e for e in c_exports if e not in external_symbols]
  c_exports += settings.REQUIRED_EXPORTS
  if settings.MAIN_MODULE:
    c_exports += side_module_external_deps(external_symbols)
  for export in c_exports:
    if settings.ERROR_ON_UNDEFINED_SYMBOLS:
      cmd.append('--export=' + export)
    else:
      cmd.append('--export-if-defined=' + export)

  for e in settings.EXPORT_IF_DEFINED:
    cmd.append('--export-if-defined=' + e)

  if settings.RELOCATABLE:
    cmd.append('--experimental-pic')
    cmd.append('--unresolved-symbols=import-dynamic')
    if not settings.WASM_BIGINT:
      # When we don't have WASM_BIGINT available, JS signature legalization
      # in binaryen will mutate the signatures of the imports/exports of our
      # shared libraries.  Because of this we need to disabled signature
      # checking of shared library functions in this case.
      cmd.append('--no-shlib-sigcheck')
    if settings.SIDE_MODULE:
      cmd.append('-shared')
    else:
      cmd.append('-pie')
    if not settings.LINKABLE:
      cmd.append('--no-export-dynamic')
  else:
    cmd.append('--export-table')
    if settings.ALLOW_TABLE_GROWTH:
      cmd.append('--growable-table')

  if not settings.SIDE_MODULE:
    cmd += ['-z', 'stack-size=%s' % settings.STACK_SIZE]

    if settings.ALLOW_MEMORY_GROWTH:
      cmd += ['--max-memory=%d' % settings.MAXIMUM_MEMORY]
    else:
      cmd += ['--no-growable-memory']

    if settings.INITIAL_HEAP != -1:
      cmd += ['--initial-heap=%d' % settings.INITIAL_HEAP]
    if settings.INITIAL_MEMORY != -1:
      cmd += ['--initial-memory=%d' % settings.INITIAL_MEMORY]

    if settings.STANDALONE_WASM:
      # when settings.EXPECT_MAIN is set we fall back to wasm-ld default of _start
      if not settings.EXPECT_MAIN:
        cmd += ['--entry=_initialize']
    else:
      if settings.PROXY_TO_PTHREAD:
        cmd += ['--entry=_emscripten_proxy_main']
      else:
        # TODO(sbc): Avoid passing --no-entry when we know we have an entry point.
        # For now we need to do this since the entry point can be either `main` or
        # `__main_argv_argc`, but we should address that by using a single `_start`
        # function like we do in STANDALONE_WASM mode.
        cmd += ['--no-entry']

  if settings.STACK_FIRST:
    cmd.append('--stack-first')

  if not settings.RELOCATABLE:
    cmd.append('--table-base=%s' % settings.TABLE_BASE)
    if not settings.STACK_FIRST:
      cmd.append('--global-base=%s' % settings.GLOBAL_BASE)

  return cmd


def link_lld(args, target, external_symbols=None):
  if not os.path.exists(WASM_LD):
    exit_with_error('linker binary not found in LLVM directory: %s', WASM_LD)
  # runs lld to link things.
  # lld doesn't currently support --start-group/--end-group since the
  # semantics are more like the windows linker where there is no need for
  # grouping.
  args = [a for a in args if a not in ('--start-group', '--end-group')]

  # Emscripten currently expects linkable output (SIDE_MODULE/MAIN_MODULE) to
  # include all archive contents.
  if settings.LINKABLE:
    args.insert(0, '--whole-archive')
    args.append('--no-whole-archive')

  if settings.STRICT and '--no-fatal-warnings' not in args:
    args.append('--fatal-warnings')

  if any(a in args for a in ('--strip-all', '-s')):
    # Tell wasm-ld to always generate a target_features section even if --strip-all/-s
    # is passed.
    args.append('--keep-section=target_features')

  cmd = [WASM_LD, '-o', target] + args
  for a in llvm_backend_args():
    cmd += ['-mllvm', a]

  if settings.WASM_EXCEPTIONS:
    cmd += ['-mllvm', '-wasm-enable-eh']
  if settings.WASM_EXCEPTIONS or settings.SUPPORT_LONGJMP == 'wasm':
    cmd += ['-mllvm', '-exception-model=wasm']

  if settings.MEMORY64:
    cmd.append('-mwasm64')

  # For relocatable output (generating an object file) we don't pass any of the
  # normal linker flags that are used when building and executable
  if '--relocatable' not in args and '-r' not in args:
    cmd += lld_flags_for_executable(external_symbols)

  cmd = get_command_with_possible_response_file(cmd)
  check_call(cmd)


def get_command_with_possible_response_file(cmd):
  # One of None, 0 or 1. (None: do default decision, 0: force disable, 1: force enable)
  force_response_files = os.getenv('EM_FORCE_RESPONSE_FILES')

  # Different OS have different limits. The most limiting usually is Windows one
  # which is set at 8191 characters. We could just use that, but it leads to
  # problems when invoking shell wrappers (e.g. emcc.bat), which, in turn,
  # pass arguments to some longer command like `(full path to Clang) ...args`.
  # In that scenario, even if the initial command line is short enough, the
  # subprocess can still run into the Command Line Too Long error.
  # Reduce the limit by ~1K for now to be on the safe side, but we might need to
  # adjust this in the future if it turns out not to be enough.
  if (len(shared.shlex_join(cmd)) <= 7000 and force_response_files != '1') or force_response_files == '0':
    return cmd

  logger.debug('using response file for %s' % cmd[0])
  filename = response_file.create_response_file(cmd[1:], shared.TEMP_DIR)
  new_cmd = [cmd[0], "@" + filename]
  return new_cmd


def emar(action, output_filename, filenames, stdout=None, stderr=None, env=None):
  utils.delete_file(output_filename)
  cmd = [EMAR, action, output_filename] + filenames
  cmd = get_command_with_possible_response_file(cmd)
  run_process(cmd, stdout=stdout, stderr=stderr, env=env)

  if 'c' in action:
    assert os.path.exists(output_filename), 'emar could not create output file: ' + output_filename


def opt_level_to_str(opt_level, shrink_level=0):
  # convert opt_level/shrink_level pair to a string argument like -O1
  if opt_level == 0:
    return '-O0'
  if shrink_level == 1:
    return '-Os'
  elif shrink_level >= 2:
    return '-Oz'
  else:
    return f'-O{min(opt_level, 3)}'


def js_optimizer(filename, passes):
  from . import js_optimizer
  try:
    return js_optimizer.run_on_file(filename, passes)
  except subprocess.CalledProcessError as e:
    exit_with_error("'%s' failed (%d)", ' '.join(e.cmd), e.returncode)


# run JS optimizer on some JS, ignoring asm.js contents if any - just run on it all
def acorn_optimizer(filename, passes, extra_info=None, return_output=False, worker_js=False):
  optimizer = path_from_root('tools/acorn-optimizer.mjs')
  original_filename = filename
  if extra_info is not None:
    temp_files = shared.get_temp_files()
    temp = temp_files.get('.js', prefix='emcc_acorn_info_').name
    shutil.copyfile(filename, temp)
    with open(temp, 'a') as f:
      f.write('// EXTRA_INFO: ' + extra_info)
    filename = temp
  cmd = config.NODE_JS + [optimizer, filename] + passes
  if not worker_js:
    # Keep JS code comments intact through the acorn optimization pass so that
    # JSDoc comments will be carried over to a later Closure run.
    if settings.MAYBE_CLOSURE_COMPILER:
      cmd += ['--closure-friendly']
    if settings.EXPORT_ES6:
      cmd += ['--export-es6']
  if settings.VERBOSE:
    cmd += ['--verbose']
  if return_output:
    return check_call(cmd, stdout=PIPE).stdout

  acorn_optimizer.counter += 1
  basename = shared.unsuffixed(original_filename)
  if '.jso' in basename:
    basename = shared.unsuffixed(basename)
  output_file = basename + '.jso%d.js' % acorn_optimizer.counter
  shared.get_temp_files().note(output_file)
  cmd += ['-o', output_file]
  check_call(cmd)
  save_intermediate(output_file, '%s.js' % passes[0])
  return output_file


acorn_optimizer.counter = 0  # type: ignore

WASM_CALL_CTORS = '__wasm_call_ctors'


# evals ctors. if binaryen_bin is provided, it is the dir of the binaryen tool
# for this, and we are in wasm mode
def eval_ctors(js_file, wasm_file, debug_info):
  if settings.MINIMAL_RUNTIME:
    CTOR_ADD_PATTERN = f"wasmExports['{WASM_CALL_CTORS}']();" # TODO test
  else:
    CTOR_ADD_PATTERN = f"addOnInit(wasmExports['{WASM_CALL_CTORS}']);"

  js = utils.read_file(js_file)

  has_wasm_call_ctors = False

  # eval the ctor caller as well as main, or, in standalone mode, the proper
  # entry/init function
  if not settings.STANDALONE_WASM:
    ctors = []
    kept_ctors = []
    has_wasm_call_ctors = CTOR_ADD_PATTERN in js
    if has_wasm_call_ctors:
      ctors += [WASM_CALL_CTORS]
    if settings.HAS_MAIN:
      main = 'main'
      if '__main_argc_argv' in settings.WASM_EXPORTS:
        main = '__main_argc_argv'
      ctors += [main]
      # TODO perhaps remove the call to main from the JS? or is this an abi
      #      we want to preserve?
      kept_ctors += [main]
    if not ctors:
      logger.info('ctor_evaller: no ctors')
      return
    args = ['--ctors=' + ','.join(ctors)]
    if kept_ctors:
      args += ['--kept-exports=' + ','.join(kept_ctors)]
  else:
    if settings.EXPECT_MAIN:
      ctor = '_start'
    else:
      ctor = '_initialize'
    args = ['--ctors=' + ctor, '--kept-exports=' + ctor]
  if settings.EVAL_CTORS == 2:
    args += ['--ignore-external-input']
  logger.info('ctor_evaller: trying to eval global ctors (' + ' '.join(args) + ')')
  out = run_binaryen_command('wasm-ctor-eval', wasm_file, wasm_file, args=args, stdout=PIPE, debug=debug_info)
  logger.info('\n\n' + out)
  num_successful = out.count('success on')
  if num_successful and has_wasm_call_ctors:
    js = js.replace(CTOR_ADD_PATTERN, '')
  utils.write_file(js_file, js)


def get_closure_compiler():
  # First check if the user configured a specific CLOSURE_COMPILER in their settings
  if config.CLOSURE_COMPILER:
    return config.CLOSURE_COMPILER

  # Otherwise use the one installed via npm
  cmd = shared.get_npm_cmd('google-closure-compiler')
  if not WINDOWS:
    # Work around an issue that Closure compiler can take up a lot of memory and crash in an error
    # "FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap
    # out of memory"
    cmd.insert(-1, '--max_old_space_size=8192')
  return cmd


def check_closure_compiler(cmd, args, env, allowed_to_fail):
  cmd = cmd + args + ['--version']
  try:
    output = run_process(cmd, stdout=PIPE, env=env).stdout
  except Exception as e:
    if allowed_to_fail:
      return False
    if isinstance(e, subprocess.CalledProcessError):
      sys.stderr.write(e.stdout)
    sys.stderr.write(str(e) + '\n')
    exit_with_error('closure compiler (%s) did not execute properly!' % shared.shlex_join(cmd))

  if 'Version:' not in output:
    if allowed_to_fail:
      return False
    exit_with_error('unrecognized closure compiler --version output (%s):\n%s' % (shared.shlex_join(cmd), output))

  return True


# Remove this once we require python3.7 and can use std.isascii.
# See: https://docs.python.org/3/library/stdtypes.html#str.isascii
def isascii(s):
  try:
    s.encode('ascii')
  except UnicodeEncodeError:
    return False
  else:
    return True


def get_closure_compiler_and_env(user_args):
  env = shared.env_with_node_in_path()
  closure_cmd = get_closure_compiler()

  native_closure_compiler_works = check_closure_compiler(closure_cmd, user_args, env, allowed_to_fail=True)
  if not native_closure_compiler_works and not any(a.startswith('--platform') for a in user_args):
    # Run with Java Closure compiler as a fallback if the native version does not work.
    # This can happen, for example, on arm64 macOS machines that do not have Rosetta installed.
    logger.warn('falling back to java version of closure compiler')
    user_args.append('--platform=java')
    check_closure_compiler(closure_cmd, user_args, env, allowed_to_fail=False)

  return closure_cmd, env


def version_split(v):
  """Split version setting number (e.g. 162000) into versions string (e.g. "16.2.0")
  """
  v = str(v).rjust(6, '0')
  assert len(v) == 6
  m = re.match(r'(\d{2})(\d{2})(\d{2})', v)
  major, minor, rev = m.group(1, 2, 3)
  return f'{int(major)}.{int(minor)}.{int(rev)}'


@ToolchainProfiler.profile()
def transpile(filename):
  config = {
    'sourceType': 'script',
    'targets': {}
  }
  if settings.MIN_CHROME_VERSION != UNSUPPORTED:
    config['targets']['chrome'] = str(settings.MIN_CHROME_VERSION)
  if settings.MIN_FIREFOX_VERSION != UNSUPPORTED:
    config['targets']['firefox'] = str(settings.MIN_FIREFOX_VERSION)
  if settings.MIN_IE_VERSION != UNSUPPORTED:
    config['targets']['ie'] = str(settings.MIN_IE_VERSION)
  if settings.MIN_SAFARI_VERSION != UNSUPPORTED:
    config['targets']['safari'] = version_split(settings.MIN_SAFARI_VERSION)
  if settings.MIN_NODE_VERSION != UNSUPPORTED:
    config['targets']['node'] = version_split(settings.MIN_NODE_VERSION)
  config_json = json.dumps(config, indent=2)
  outfile = shared.get_temp_files().get('babel.js').name
  config_file = shared.get_temp_files().get('babel_config.json').name
  logger.debug(config_json)
  utils.write_file(config_file, config_json)
  cmd = shared.get_npm_cmd('babel') + [filename, '-o', outfile, '--presets', '@babel/preset-env', '--config-file', config_file]
  check_call(cmd, cwd=path_from_root())
  return outfile


@ToolchainProfiler.profile()
def closure_compiler(filename, advanced=True, extra_closure_args=None):
  user_args = []
  env_args = os.environ.get('EMCC_CLOSURE_ARGS')
  if env_args:
    user_args += shlex.split(env_args)
  if extra_closure_args:
    user_args += extra_closure_args

  closure_cmd, env = get_closure_compiler_and_env(user_args)

  # Closure externs file contains known symbols to be extern to the minification, Closure
  # should not minify these symbol names.
  CLOSURE_EXTERNS = [path_from_root('src/closure-externs/closure-externs.js')]

  if settings.MODULARIZE:
    CLOSURE_EXTERNS += [path_from_root('src/closure-externs/modularize-externs.js')]

  if settings.USE_WEBGPU:
    CLOSURE_EXTERNS += [path_from_root('src/closure-externs/webgpu-externs.js')]

  # Closure compiler needs to know about all exports that come from the wasm module, because to optimize for small code size,
  # the exported symbols are added to global scope via a foreach loop in a way that evades Closure's static analysis. With an explicit
  # externs file for the exports, Closure is able to reason about the exports.
  if settings.WASM_EXPORTS and not settings.DECLARE_ASM_MODULE_EXPORTS:
    # Generate an exports file that records all the exported symbols from the wasm module.
    module_exports_suppressions = '\n'.join(['/**\n * @suppress {duplicate, undefinedVars}\n */\nvar %s;\n' % asmjs_mangle(i) for i in settings.WASM_EXPORTS])
    exports_file = shared.get_temp_files().get('.js', prefix='emcc_module_exports_')
    exports_file.write(module_exports_suppressions.encode())
    exports_file.close()

    CLOSURE_EXTERNS += [exports_file.name]

  # Node.js specific externs
  if shared.target_environment_may_be('node'):
    NODE_EXTERNS_BASE = path_from_root('third_party/closure-compiler/node-externs')
    NODE_EXTERNS = os.listdir(NODE_EXTERNS_BASE)
    NODE_EXTERNS = [os.path.join(NODE_EXTERNS_BASE, name) for name in NODE_EXTERNS
                    if name.endswith('.js')]
    CLOSURE_EXTERNS += [path_from_root('src/closure-externs/node-externs.js')] + NODE_EXTERNS

  # V8/SpiderMonkey shell specific externs
  if shared.target_environment_may_be('shell'):
    V8_EXTERNS = [path_from_root('src/closure-externs/v8-externs.js')]
    SPIDERMONKEY_EXTERNS = [path_from_root('src/closure-externs/spidermonkey-externs.js')]
    CLOSURE_EXTERNS += V8_EXTERNS + SPIDERMONKEY_EXTERNS

  # Web environment specific externs
  if shared.target_environment_may_be('web') or shared.target_environment_may_be('worker'):
    BROWSER_EXTERNS_BASE = path_from_root('src/closure-externs/browser-externs')
    if os.path.isdir(BROWSER_EXTERNS_BASE):
      BROWSER_EXTERNS = os.listdir(BROWSER_EXTERNS_BASE)
      BROWSER_EXTERNS = [os.path.join(BROWSER_EXTERNS_BASE, name) for name in BROWSER_EXTERNS
                         if name.endswith('.js')]
      CLOSURE_EXTERNS += BROWSER_EXTERNS

  if settings.DYNCALLS:
    CLOSURE_EXTERNS += [path_from_root('src/closure-externs/dyncall-externs.js')]

  args = ['--compilation_level', 'ADVANCED_OPTIMIZATIONS' if advanced else 'SIMPLE_OPTIMIZATIONS']
  # Keep in sync with ecmaVersion in tools/acorn-optimizer.mjs
  args += ['--language_in', 'ECMASCRIPT_2021']
  # We do transpilation using babel
  args += ['--language_out', 'NO_TRANSPILE']
  # Tell closure never to inject the 'use strict' directive.
  args += ['--emit_use_strict=false']

  if settings.IGNORE_CLOSURE_COMPILER_ERRORS:
    args.append('--jscomp_off=*')
  # Specify input file relative to the temp directory to avoid specifying non-7-bit-ASCII path names.
  for e in CLOSURE_EXTERNS:
    args += ['--externs', e]
  args += user_args

  cmd = closure_cmd + args
  return run_closure_cmd(cmd, filename, env)


def run_closure_cmd(cmd, filename, env):
  cmd += ['--js', filename]

  # Closure compiler is unable to deal with path names that are not 7-bit ASCII:
  # https://github.com/google/closure-compiler/issues/3784
  tempfiles = shared.get_temp_files()

  def move_to_safe_7bit_ascii_filename(filename):
    if isascii(filename):
      return os.path.abspath(filename)
    safe_filename = tempfiles.get('.js').name  # Safe 7-bit filename
    shutil.copyfile(filename, safe_filename)
    return os.path.relpath(safe_filename, tempfiles.tmpdir)

  for i in range(len(cmd)):
    for prefix in ('--externs', '--js'):
      # Handle the case where the flag and the value are two separate arguments.
      if cmd[i] == prefix:
        cmd[i + 1] = move_to_safe_7bit_ascii_filename(cmd[i + 1])
      # and the case where they are one argument, e.g. --externs=foo.js
      elif cmd[i].startswith(prefix + '='):
        # Replace the argument with a version that has a safe filename.
        filename = cmd[i].split('=', 1)[1]
        cmd[i] = '='.join([prefix, move_to_safe_7bit_ascii_filename(filename)])

  outfile = tempfiles.get('.cc.js').name  # Safe 7-bit filename

  # Specify output file relative to the temp directory to avoid specifying non-7-bit-ASCII path names.
  cmd += ['--js_output_file', os.path.relpath(outfile, tempfiles.tmpdir)]
  if not settings.MINIFY_WHITESPACE:
    cmd += ['--formatting', 'PRETTY_PRINT']

  shared.print_compiler_stage(cmd)

  # Closure compiler does not work if any of the input files contain characters outside the
  # 7-bit ASCII range. Therefore make sure the command line we pass does not contain any such
  # input files by passing all input filenames relative to the cwd. (user temp directory might
  # be in user's home directory, and user's profile name might contain unicode characters)
  proc = run_process(cmd, stderr=PIPE, check=False, env=env, cwd=tempfiles.tmpdir)

  # XXX Closure bug: if Closure is invoked with --create_source_map, Closure should create a
  # outfile.map source map file (https://github.com/google/closure-compiler/wiki/Source-Maps)
  # But it looks like it creates such files on Linux(?) even without setting that command line
  # flag (and currently we don't), so delete the produced source map file to not leak files in
  # temp directory.
  utils.delete_file(outfile + '.map')

  closure_warnings = diagnostics.manager.warnings['closure']

  # Print Closure diagnostics result up front.
  if proc.returncode != 0:
    logger.error('Closure compiler run failed:\n')
  elif len(proc.stderr.strip()) > 0 and closure_warnings['enabled']:
    if closure_warnings['error']:
      logger.error('Closure compiler completed with warnings and -Werror=closure enabled, aborting!\n')
    else:
      logger.warn('Closure compiler completed with warnings:\n')

  # Print input file (long wall of text!)
  if DEBUG == 2 and (proc.returncode != 0 or (len(proc.stderr.strip()) > 0 and closure_warnings['enabled'])):
    input_file = open(filename, 'r').read().splitlines()
    for i in range(len(input_file)):
      sys.stderr.write(f'{i + 1}: {input_file[i]}\n')

  if proc.returncode != 0:
    logger.error(proc.stderr) # print list of errors (possibly long wall of text if input was minified)

    # Exit and print final hint to get clearer output
    msg = f'closure compiler failed (rc: {proc.returncode}): {shared.shlex_join(cmd)}'
    if settings.MINIFY_WHITESPACE:
      msg += ' the error message may be clearer with -g1 and EMCC_DEBUG=2 set'
    exit_with_error(msg)

  if len(proc.stderr.strip()) > 0 and closure_warnings['enabled']:
    # print list of warnings (possibly long wall of text if input was minified)
    if closure_warnings['error']:
      logger.error(proc.stderr)
    else:
      logger.warn(proc.stderr)

    # Exit and/or print final hint to get clearer output
    if settings.MINIFY_WHITESPACE:
      logger.warn('(rerun with -g1 linker flag for an unminified output)')
    elif DEBUG != 2:
      logger.warn('(rerun with EMCC_DEBUG=2 enabled to dump Closure input file)')

    if closure_warnings['error']:
      exit_with_error('closure compiler produced warnings and -W=error=closure enabled')

  return outfile


# minify the final wasm+JS combination. this is done after all the JS
# and wasm optimizations; here we do the very final optimizations on them
def minify_wasm_js(js_file, wasm_file, expensive_optimizations, debug_info):
  # start with JSDCE, to clean up obvious JS garbage. When optimizing for size,
  # use AJSDCE (aggressive JS DCE, performs multiple iterations). Clean up
  # whitespace if necessary too.
  passes = []
  if not settings.LINKABLE:
    passes.append('JSDCE' if not expensive_optimizations else 'AJSDCE')
  # Don't minify if we are going to run closure compiler afterwards
  minify = settings.MINIFY_WHITESPACE and not settings.MAYBE_CLOSURE_COMPILER
  if minify:
    passes.append('--minify-whitespace')
  if passes:
    logger.debug('running cleanup on shell code: ' + ' '.join(passes))
    js_file = acorn_optimizer(js_file, passes)
  # if we can optimize this js+wasm combination under the assumption no one else
  # will see the internals, do so
  if not settings.LINKABLE:
    # if we are optimizing for size, shrink the combined wasm+JS
    # TODO: support this when a symbol map is used
    if expensive_optimizations:
      js_file = metadce(js_file,
                        wasm_file,
                        debug_info=debug_info,
                        last=not settings.MINIFY_WASM_IMPORTS_AND_EXPORTS)
      # now that we removed unneeded communication between js and wasm, we can clean up
      # the js some more.
      passes = ['AJSDCE']
      if minify:
        passes.append('--minify-whitespace')
      logger.debug('running post-meta-DCE cleanup on shell code: ' + ' '.join(passes))
      js_file = acorn_optimizer(js_file, passes)
      if settings.MINIFY_WASM_IMPORTS_AND_EXPORTS:
        js_file = minify_wasm_imports_and_exports(js_file, wasm_file,
                                                  minify_exports=settings.MINIFY_WASM_EXPORT_NAMES,
                                                  debug_info=debug_info)
  return js_file


def is_internal_global(name):
  internal_start_stop_symbols = set(['__start_em_asm', '__stop_em_asm',
                                     '__start_em_js', '__stop_em_js',
                                     '__start_em_lib_deps', '__stop_em_lib_deps',
                                     '__em_lib_deps'])
  internal_prefixes = ('__em_js__', '__em_lib_deps')
  return name in internal_start_stop_symbols or any(name.startswith(p) for p in internal_prefixes)


# get the flags to pass into the very last binaryen tool invocation, that runs
# the final set of optimizations
def get_last_binaryen_opts():
  return [f'--optimize-level={settings.OPT_LEVEL}',
          f'--shrink-level={settings.SHRINK_LEVEL}',
          '--optimize-stack-ir']


# run binaryen's wasm-metadce to dce both js and wasm
def metadce(js_file, wasm_file, debug_info, last):
  logger.debug('running meta-DCE')
  temp_files = shared.get_temp_files()
  # first, get the JS part of the graph
  if settings.MAIN_MODULE:
    # For the main module we include all exports as possible roots, not just function exports.
    # This means that any usages of data symbols within the JS or in the side modules can/will keep
    # these exports alive on the wasm module.
    # This is important today for weak data symbols that are defined by the main and the side module
    # (i.e.  RTTI info).  We want to make sure the main module's symbols get added to wasmImports
    # when the main module is loaded.  If this doesn't happen then the symbols in the side module
    # will take precedence.
    exports = settings.WASM_EXPORTS
  else:
    # Ignore exported wasm globals.  Those get inlined directly into the JS code.
    exports = sorted(set(settings.WASM_EXPORTS) - set(settings.WASM_GLOBAL_EXPORTS))

  extra_info = '{ "exports": [' + ','.join(f'["{asmjs_mangle(x)}", "{x}"]' for x in exports) + ']}'

  txt = acorn_optimizer(js_file, ['emitDCEGraph', '--no-print'], return_output=True, extra_info=extra_info)
  graph = json.loads(txt)
  # ensure that functions expected to be exported to the outside are roots
  required_symbols = user_requested_exports.union(set(settings.SIDE_MODULE_IMPORTS))
  for item in graph:
    if 'export' in item:
      export = asmjs_mangle(item['export'])
      if settings.EXPORT_ALL or export in required_symbols:
        item['root'] = True

  # fix wasi imports TODO: support wasm stable with an option?
  WASI_IMPORTS = {
    'environ_get',
    'environ_sizes_get',
    'args_get',
    'args_sizes_get',
    'fd_write',
    'fd_close',
    'fd_read',
    'fd_seek',
    'fd_fdstat_get',
    'fd_sync',
    'fd_pread',
    'fd_pwrite',
    'proc_exit',
    'clock_res_get',
    'clock_time_get',
    'path_open',
  }
  for item in graph:
    if 'import' in item and item['import'][1] in WASI_IMPORTS:
      item['import'][0] = settings.WASI_MODULE_NAME

  # map import/export names to native wasm symbols.
  import_name_map = {}
  export_name_map = {}
  for item in graph:
    if 'import' in item:
      name = item['import'][1]
      import_name_map[item['name']] = name
      if asmjs_mangle(name) in settings.SIDE_MODULE_IMPORTS:
        item['root'] = True
    elif 'export' in item:
      export_name_map[item['name']] = item['export']
  temp = temp_files.get('.json', prefix='emcc_dce_graph_').name
  utils.write_file(temp, json.dumps(graph, indent=2))
  # run wasm-metadce
  args = ['--graph-file=' + temp]
  if last:
    args += get_last_binaryen_opts()
  out = run_binaryen_command('wasm-metadce',
                             wasm_file,
                             wasm_file,
                             args,
                             debug=debug_info,
                             stdout=PIPE)
  # find the unused things in js
  unused_imports = []
  unused_exports = []
  PREFIX = 'unused: '
  for line in out.splitlines():
    if line.startswith(PREFIX):
      name = line.replace(PREFIX, '').strip()
      # With dynamic linking we never want to strip the memory or the table
      # This can be removed once SIDE_MODULE_IMPORTS includes tables and memories.
      if settings.MAIN_MODULE and name.split('$')[-1] in ('wasmMemory', 'wasmTable'):
        continue
      # we only remove imports and exports in applyDCEGraphRemovals
      if name.startswith('emcc$import$'):
        native_name = import_name_map[name]
        unused_imports.append(native_name)
      elif name.startswith('emcc$export$'):
        if settings.DECLARE_ASM_MODULE_EXPORTS:
          native_name = export_name_map[name]
          if not is_internal_global(native_name):
            unused_exports.append(native_name)
  if not unused_exports and not unused_imports:
    # nothing found to be unused, so we have nothing to remove
    return js_file
  # remove them
  passes = ['applyDCEGraphRemovals']
  if settings.MINIFY_WHITESPACE:
    passes.append('--minify-whitespace')
  if DEBUG:
    logger.debug("unused_imports: %s", str(unused_imports))
    logger.debug("unused_exports: %s", str(unused_exports))
  extra_info = {'unusedImports': unused_imports, 'unusedExports': unused_exports}
  return acorn_optimizer(js_file, passes, extra_info=json.dumps(extra_info))


def asyncify_lazy_load_code(wasm_target, debug):
  # create the lazy-loaded wasm. remove the memory segments from it, as memory
  # segments have already been applied by the initial wasm, and apply the knowledge
  # that it will only rewind, after which optimizations can remove some code
  args = ['--remove-memory', '--mod-asyncify-never-unwind']
  if settings.OPT_LEVEL > 0:
    args.append(opt_level_to_str(settings.OPT_LEVEL, settings.SHRINK_LEVEL))
  run_wasm_opt(wasm_target,
               wasm_target + '.lazy.wasm',
               args=args,
               debug=debug)
  # re-optimize the original, by applying the knowledge that imports will
  # definitely unwind, and we never rewind, after which optimizations can remove
  # a lot of code
  # TODO: support other asyncify stuff, imports that don't always unwind?
  # TODO: source maps etc.
  args = ['--mod-asyncify-always-and-only-unwind']
  if settings.OPT_LEVEL > 0:
    args.append(opt_level_to_str(settings.OPT_LEVEL, settings.SHRINK_LEVEL))
  run_wasm_opt(infile=wasm_target,
               outfile=wasm_target,
               args=args,
               debug=debug)


def minify_wasm_imports_and_exports(js_file, wasm_file, minify_exports, debug_info):
  logger.debug('minifying wasm imports and exports')
  # run the pass
  args = []
  if minify_exports:
    # standalone wasm mode means we need to emit a wasi import module.
    # otherwise, minify even the imported module names.
    if settings.MINIFY_WASM_IMPORTED_MODULES:
      args.append('--minify-imports-and-exports-and-modules')
    else:
      args.append('--minify-imports-and-exports')
  else:
    args.append('--minify-imports')
  # this is always the last tool we run (if we run it)
  args += get_last_binaryen_opts()
  out = run_wasm_opt(wasm_file, wasm_file, args, debug=debug_info, stdout=PIPE)

  # get the mapping
  SEP = ' => '
  mapping = {}
  for line in out.split('\n'):
    if SEP in line:
      old, new = line.strip().split(SEP)
      assert old not in mapping, 'imports must be unique'
      mapping[old] = new
  # apply them
  passes = ['applyImportAndExportNameChanges']
  if settings.MINIFY_WHITESPACE:
    passes.append('--minify-whitespace')
  extra_info = {'mapping': mapping}
  if settings.MINIFICATION_MAP:
    lines = [f'{new}:{old}' for old, new in mapping.items()]
    utils.write_file(settings.MINIFICATION_MAP, '\n'.join(lines) + '\n')
  return acorn_optimizer(js_file, passes, extra_info=json.dumps(extra_info))


def wasm2js(js_file, wasm_file, opt_level, use_closure_compiler, debug_info, symbols_file=None, symbols_file_js=None):
  logger.debug('wasm2js')
  args = ['--emscripten']
  if opt_level > 0:
    args += ['-O']
  if symbols_file:
    args += ['--symbols-file=%s' % symbols_file]
  wasm2js_js = run_binaryen_command('wasm2js', wasm_file,
                                    args=args,
                                    debug=debug_info,
                                    stdout=PIPE)
  if DEBUG:
    utils.write_file(os.path.join(get_emscripten_temp_dir(), 'wasm2js-output.js'), wasm2js_js)
  # JS optimizations
  if opt_level >= 2:
    passes = []
    if not debug_info and not settings.PTHREADS:
      passes += ['minifyNames']
      if symbols_file_js:
        passes += ['symbolMap=%s' % symbols_file_js]
    if settings.MINIFY_WHITESPACE:
      passes += ['--minify-whitespace']
    if passes:
      # hackish fixups to work around wasm2js style and the js optimizer FIXME
      wasm2js_js = f'// EMSCRIPTEN_START_ASM\n{wasm2js_js}// EMSCRIPTEN_END_ASM\n'
      wasm2js_js = wasm2js_js.replace('\n function $', '\nfunction $')
      wasm2js_js = wasm2js_js.replace('\n }', '\n}')
      temp = shared.get_temp_files().get('.js').name
      utils.write_file(temp, wasm2js_js)
      temp = js_optimizer(temp, passes)
      wasm2js_js = utils.read_file(temp)
  # Closure compiler: in mode 1, we just minify the shell. In mode 2, we
  # minify the wasm2js output as well, which is ok since it isn't
  # validating asm.js.
  # TODO: in the non-closure case, we could run a lightweight general-
  #       purpose JS minifier here.
  if use_closure_compiler == 2:
    temp = shared.get_temp_files().get('.js').name
    with open(temp, 'a') as f:
      f.write(wasm2js_js)
    temp = closure_compiler(temp, advanced=False)
    wasm2js_js = utils.read_file(temp)
    # closure may leave a trailing `;`, which would be invalid given where we place
    # this code (inside parens)
    wasm2js_js = wasm2js_js.strip()
    if wasm2js_js[-1] == ';':
      wasm2js_js = wasm2js_js[:-1]
  all_js = utils.read_file(js_file)
  # quoted notation, something like Module['__wasm2jsInstantiate__']
  finds = re.findall(r'''[\w\d_$]+\[['"]__wasm2jsInstantiate__['"]\]''', all_js)
  if not finds:
    # post-closure notation, something like a.__wasm2jsInstantiate__
    finds = re.findall(r'''[\w\d_$]+\.__wasm2jsInstantiate__''', all_js)
  assert len(finds) == 1
  marker = finds[0]
  all_js = all_js.replace(marker, f'(\n{wasm2js_js}\n)')
  # replace the placeholder with the actual code
  js_file = js_file + '.wasm2js.js'
  utils.write_file(js_file, all_js)
  return js_file


def strip(infile, outfile, debug=False, sections=None):
  """Strip DWARF and/or other specified sections from a wasm file"""
  cmd = [LLVM_OBJCOPY, infile, outfile]
  if debug:
    cmd += ['--remove-section=.debug*']
  if sections:
    cmd += ['--remove-section=' + section for section in sections]
  check_call(cmd)


# extract the DWARF info from the main file, and leave the wasm with
# debug into as a file on the side
def emit_debug_on_side(wasm_file, wasm_file_with_dwarf):
  embedded_path = settings.SEPARATE_DWARF_URL
  if not embedded_path:
    # a path was provided - make it relative to the wasm.
    embedded_path = os.path.relpath(wasm_file_with_dwarf,
                                    os.path.dirname(wasm_file))
    # normalize the path to use URL-style separators, per the spec
    embedded_path = utils.normalize_path(embedded_path)

  shutil.move(wasm_file, wasm_file_with_dwarf)
  strip(wasm_file_with_dwarf, wasm_file, debug=True)

  # Strip code and data from the debug file to limit its size. The other known
  # sections are still required to correctly interpret the DWARF info.
  # TODO(dschuff): Also strip the DATA section? To make this work we'd need to
  # either allow "invalid" data segment name entries, or maybe convert the DATA
  # to a DATACOUNT section.
  # TODO(https://github.com/emscripten-core/emscripten/issues/13084): Re-enable
  # this code once the debugger extension can handle wasm files with name
  # sections but no code sections.
  # strip(wasm_file_with_dwarf, wasm_file_with_dwarf, sections=['CODE'])

  # embed a section in the main wasm to point to the file with external DWARF,
  # see https://yurydelendik.github.io/webassembly-dwarf/#external-DWARF
  section_name = b'\x13external_debug_info' # section name, including prefixed size
  filename_bytes = embedded_path.encode('utf-8')
  contents = webassembly.to_leb(len(filename_bytes)) + filename_bytes
  section_size = len(section_name) + len(contents)
  with open(wasm_file, 'ab') as f:
    f.write(b'\0') # user section is code 0
    f.write(webassembly.to_leb(section_size))
    f.write(section_name)
    f.write(contents)


def little_endian_heap(js_file):
  logger.debug('enforcing little endian heap byte order')
  return acorn_optimizer(js_file, ['littleEndianHeap'])


def apply_wasm_memory_growth(js_file):
  logger.debug('supporting wasm memory growth with pthreads')
  fixed = acorn_optimizer(js_file, ['growableHeap'])
  ret = js_file + '.pgrow.js'
  fixed = utils.read_file(fixed)
  support_code = utils.read_file(path_from_root('src/growableHeap.js'))
  utils.write_file(ret, support_code + '\n' + fixed)
  return ret


def use_unsigned_pointers_in_js(js_file):
  logger.debug('using unsigned pointers in JS')
  return acorn_optimizer(js_file, ['unsignPointers'])


def instrument_js_for_asan(js_file):
  logger.debug('instrumenting JS memory accesses for ASan')
  return acorn_optimizer(js_file, ['asanify'])


def instrument_js_for_safe_heap(js_file):
  logger.debug('instrumenting JS memory accesses for SAFE_HEAP')
  return acorn_optimizer(js_file, ['safeHeap'])


@ToolchainProfiler.profile()
def handle_final_wasm_symbols(wasm_file, symbols_file, debug_info):
  logger.debug('handle_final_wasm_symbols')
  args = []
  if symbols_file:
    args += ['--print-function-map']
  else:
    # suppress the wasm-opt warning regarding "no output file specified"
    args += ['--quiet']
  output = run_wasm_opt(wasm_file, args=args, stdout=PIPE)
  if symbols_file:
    utils.write_file(symbols_file, output)
  if not debug_info:
    # strip the names section using llvm-objcopy. this is slightly slower than
    # using wasm-opt (we could run wasm-opt without -g here and just tell it to
    # write the file back out), but running wasm-opt would undo StackIR
    # optimizations, if we did those.
    strip(wasm_file, wasm_file, sections=['name'])


def is_ar(filename):
  """Return True if a the given filename is an ar archive, False otherwise.
  """
  try:
    header = open(filename, 'rb').read(8)
  except Exception as e:
    logger.debug('is_ar failed to test whether file \'%s\' is a llvm archive file! Failed on exception: %s' % (filename, e))
    return False

  return header in (b'!<arch>\n', b'!<thin>\n')


def is_wasm(filename):
  if not os.path.isfile(filename):
    return False
  header = open(filename, 'rb').read(webassembly.HEADER_SIZE)
  return header == webassembly.MAGIC + webassembly.VERSION


def is_wasm_dylib(filename):
  """Detect wasm dynamic libraries by the presence of the "dylink" custom section."""
  if not is_wasm(filename):
    return False
  with webassembly.Module(filename) as module:
    section = next(module.sections())
    if section.type == webassembly.SecType.CUSTOM:
      module.seek(section.offset)
      if module.read_string() in ('dylink', 'dylink.0'):
        return True
  return False


def emit_wasm_source_map(wasm_file, map_file, final_wasm):
  # source file paths must be relative to the location of the map (which is
  # emitted alongside the wasm)
  base_path = os.path.dirname(os.path.abspath(final_wasm))
  sourcemap_cmd = [sys.executable, '-E', path_from_root('tools/wasm-sourcemap.py'),
                   wasm_file,
                   '--dwarfdump=' + LLVM_DWARFDUMP,
                   '-o',  map_file,
                   '--basepath=' + base_path]
  check_call(sourcemap_cmd)


def get_binaryen_feature_flags():
  # settings.BINARYEN_FEATURES is empty unless features have been extracted by
  # wasm-emscripten-finalize already.
  if settings.BINARYEN_FEATURES:
    return settings.BINARYEN_FEATURES
  else:
    return ['--detect-features']


def check_binaryen(bindir):
  opt = os.path.join(bindir, exe_suffix('wasm-opt'))
  if not os.path.exists(opt):
    exit_with_error('binaryen executable not found (%s). Please check your binaryen installation' % opt)
  try:
    output = run_process([opt, '--version'], stdout=PIPE).stdout
  except subprocess.CalledProcessError:
    exit_with_error('error running binaryen executable (%s). Please check your binaryen installation' % opt)
  if output:
    output = output.splitlines()[0]
  try:
    version = output.split()[2]
    version = int(version)
  except (IndexError, ValueError):
    exit_with_error('error parsing binaryen version (%s). Please check your binaryen installation (%s)' % (output, opt))

  # Allow the expected version or the following one in order avoid needing to update both
  # emscripten and binaryen in lock step in emscripten-releases.
  if version not in (EXPECTED_BINARYEN_VERSION, EXPECTED_BINARYEN_VERSION + 1):
    diagnostics.warning('version-check', 'unexpected binaryen version: %s (expected %s)', version, EXPECTED_BINARYEN_VERSION)


def get_binaryen_bin():
  global binaryen_checked
  rtn = os.path.join(config.BINARYEN_ROOT, 'bin')
  if not binaryen_checked:
    check_binaryen(rtn)
    binaryen_checked = True
  return rtn


# track whether the last binaryen command kept debug info around. this is used
# to see whether we need to do an extra step at the end to strip it.
binaryen_kept_debug_info = False


def run_binaryen_command(tool, infile, outfile=None, args=None, debug=False, stdout=None):
  cmd = [os.path.join(get_binaryen_bin(), tool)]
  if args:
    cmd += args
  if infile:
    cmd += [infile]
  if outfile:
    cmd += ['-o', outfile]
    if settings.ERROR_ON_WASM_CHANGES_AFTER_LINK:
      # emit some extra helpful text for common issues
      extra = ''
      # a plain -O0 build *almost* doesn't need post-link changes, except for
      # legalization. show a clear error for those (as the flags the user passed
      # in are not enough to see what went wrong)
      if settings.LEGALIZE_JS_FFI:
        extra += '\nnote: to disable int64 legalization (which requires changes after link) use -sWASM_BIGINT'
      if settings.OPT_LEVEL > 1:
        extra += '\nnote: -O2+ optimizations always require changes, build with -O0 or -O1 instead'
      exit_with_error(f'changes to the wasm are required after link, but disallowed by ERROR_ON_WASM_CHANGES_AFTER_LINK: {cmd}{extra}')
  if debug:
    cmd += ['-g'] # preserve the debug info
  # if the features are not already handled, handle them
  cmd += get_binaryen_feature_flags()
  # if we are emitting a source map, every time we load and save the wasm
  # we must tell binaryen to update it
  # TODO: all tools should support source maps; wasm-ctor-eval does not atm,
  #       for example
  if settings.GENERATE_SOURCE_MAP and outfile and tool in ['wasm-opt', 'wasm-emscripten-finalize']:
    cmd += [f'--input-source-map={infile}.map']
    cmd += [f'--output-source-map={outfile}.map']
  ret = check_call(cmd, stdout=stdout).stdout
  if outfile:
    save_intermediate(outfile, '%s.wasm' % tool)
    global binaryen_kept_debug_info
    binaryen_kept_debug_info = '-g' in cmd
  return ret


def run_wasm_opt(infile, outfile=None, args=[], **kwargs):  # noqa
  return run_binaryen_command('wasm-opt', infile, outfile, args=args, **kwargs)


def save_intermediate(src, dst):
  if DEBUG:
    dst = 'emcc-%02d-%s' % (save_intermediate.counter, dst)
    save_intermediate.counter += 1
    dst = os.path.join(shared.CANONICAL_TEMP_DIR, dst)
    logger.debug('saving debug copy %s' % dst)
    shutil.copyfile(src, dst)


save_intermediate.counter = 0  # type: ignore


def js_legalization_pass_flags():
  flags = []
  if settings.RELOCATABLE:
    # When building in relocatable mode, we also want access the original
    # non-legalized wasm functions (since wasm modules can and do link to
    # the original, non-legalized, functions).
    flags += ['--pass-arg=legalize-js-interface-export-originals']
  if not settings.SIDE_MODULE:
    # Unless we are building a side module the helper functions should be
    # assumed to be defined and exports within the module, otherwise binaryen
    # assumes they are imports.
    flags += ['--pass-arg=legalize-js-interface-exported-helpers']
  return flags


# Returns a list of flags to pass to emcc that make the output run properly in
# the given node version.
def get_emcc_node_flags(node_version):
  if not node_version:
    return []
  # Convert to the format we use in our settings, XXYYZZ, for example,
  # 10.1.7 will turn into "100107".
  str_node_version = "%02d%02d%02d" % node_version
  return [f'-sMIN_NODE_VERSION={str_node_version}']