emcc.py

#!/usr/bin/env python3
# Copyright 2011 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.

"""\
emcc - compiler helper script
=============================

emcc is a drop-in replacement for a compiler like gcc or clang.

See  emcc --help  for details.

emcc can be influenced by a few environment variables:

  EMCC_DEBUG - "1" will log out useful information during compilation, as well as
               save each compiler step as an emcc-* file in the temp dir
               (by default /tmp/emscripten_temp). "2" will save additional emcc-*
               steps, that would normally not be separately produced (so this
               slows down compilation).
""" # noqa: D205, D400, D415

import logging
import os
import shlex
import shutil
import sys
import tarfile
from dataclasses import dataclass
from enum import Enum, auto, unique

# This assert needs to happen early, before any too-recent python syntax is used.
# In particular it needs to happen before we import any python file that uses the
# `match` keyword.
assert sys.version_info >= (3, 10), f'emscripten requires python 3.10 or above ({sys.executable} {sys.version})'

from tools import (
  building,
  cache,
  cmdline,
  compile,
  config,
  diagnostics,
  shared,
  system_libs,
  utils,
)
from tools.cmdline import CLANG_FLAGS_WITH_ARGS, options
from tools.response_file import substitute_response_files
from tools.settings import COMPILE_TIME_SETTINGS, default_setting, settings, user_settings
from tools.shared import DEBUG, DYLIB_EXTENSIONS, in_temp
from tools.toolchain_profiler import ToolchainProfiler
from tools.utils import exit_with_error, get_file_suffix, read_file, unsuffixed_basename

logger = logging.getLogger('emcc')

# In git checkouts of emscripten `bootstrap.py` exists to run post-checkout
# steps.  In packaged versions (e.g. emsdk) this file does not exist (because
# it is excluded in tools/install.py) and these steps are assumed to have been
# run already.
if os.path.exists(utils.path_from_root('.git')) and os.path.exists(utils.path_from_root('bootstrap.py')):
  import bootstrap
  bootstrap.check()

PREPROCESSED_EXTENSIONS = {'.i', '.ii'}
ASSEMBLY_EXTENSIONS = {'.s'}
HEADER_EXTENSIONS = {'.h', '.hxx', '.hpp', '.hh', '.H', '.HXX', '.HPP', '.HH'}
SOURCE_EXTENSIONS = {
  '.c', '.i', # C
  '.cppm', '.pcm', '.cpp', '.cxx', '.cc', '.c++', '.CPP', '.CXX', '.C', '.CC', '.C++', '.ii', # C++
  '.m', '.mi', '.mm', '.mii', # ObjC/ObjC++
  '.bc', '.ll', # LLVM IR
  '.S', # asm with preprocessor
  os.devnull, # consider the special endingless filenames like /dev/null to be C
} | PREPROCESSED_EXTENSIONS

LINK_ONLY_FLAGS = {
    '--bind', '--closure', '--cpuprofiler', '--embed-file',
    '--emit-symbol-map', '--emrun', '--exclude-file', '--extern-post-js',
    '--extern-pre-js', '--ignore-dynamic-linking', '--js-library',
    '--js-transform', '--oformat', '--output_eol', '--output-eol',
    '--post-js', '--pre-js', '--preload-file', '--profiling-funcs',
    '--proxy-to-worker', '--shell-file', '--source-map-base',
    '--threadprofiler', '--use-preload-plugins',
}


@unique
class Mode(Enum):
  # Used any time we are not linking, including PCH, pre-processing, etc
  COMPILE_ONLY = auto()
  # Only when --post-link is specified
  POST_LINK_ONLY = auto()
  # This is the default mode, in the absence of any flags such as -c, -E, etc
  COMPILE_AND_LINK = auto()


@dataclass
class LinkFlag:
  """Used to represent a linker flag.

  The flag value is stored along with a bool that distinguishes input
  files from non-files.

  A list of these is returned by separate_linker_flags.
  """

  value: str
  is_file: int


class EmccState:
  def __init__(self, args):
    self.mode = Mode.COMPILE_AND_LINK
    # Using tuple here to prevent accidental mutation
    self.orig_args = tuple(args)


def create_reproduce_file(name, args):
  def make_relative(filename):
    filename = os.path.normpath(os.path.abspath(filename))
    filename = os.path.splitdrive(filename)[1]
    filename = filename[1:]
    return filename

  root = unsuffixed_basename(name)
  with tarfile.open(name, 'w') as reproduce_file:
    reproduce_file.add(utils.path_from_root('emscripten-version.txt'), os.path.join(root, 'version.txt'))

    with shared.get_temp_files().get_file(suffix='.tar') as rsp_name:
      with open(rsp_name, 'w', encoding='utf-8') as rsp:
        ignore_next = False
        output_arg = None

        for arg in args:
          ignore = ignore_next
          ignore_next = False
          if arg.startswith('--reproduce='):
            continue

          if len(arg) > 2 and arg.startswith('-o'):
            rsp.write('-o\n')
            arg = arg[3:]
            output_arg = True
            ignore = True

          if output_arg:
            # If -o path contains directories, "emcc @response.txt" will likely
            # fail because the archive we are creating doesn't contain empty
            # directories for the output path (-o doesn't create directories).
            # Strip directories to prevent the issue.
            arg = os.path.basename(arg)
            output_arg = False

          if not arg.startswith('-') and not ignore:
            relpath = make_relative(arg)
            rsp.write(relpath + '\n')
            reproduce_file.add(arg, os.path.join(root, relpath))
          else:
            rsp.write(arg + '\n')

          if ignore:
            continue

          if arg in CLANG_FLAGS_WITH_ARGS:
            ignore_next = True

          if arg == '-o':
            output_arg = True

      reproduce_file.add(rsp_name, os.path.join(root, 'response.txt'))


@ToolchainProfiler.profile()
def main(args):
  if shared.run_via_emxx:
    clang = shared.CLANG_CXX
  else:
    clang = shared.CLANG_CC

  # Special case the handling of `-v` because it has a special/different meaning
  # when used with no other arguments.  In particular, we must handle this early
  # on, before we inject EMCC_CFLAGS.  This is because tools like cmake and
  # autoconf will run `emcc -v` to determine the compiler version and we don't
  # want that to break for users of EMCC_CFLAGS.
  if len(args) == 2 and args[1] == '-v':
    # autoconf likes to see 'GNU' in the output to enable shared object support
    print(cmdline.version_string(), file=sys.stderr)
    return shared.check_call([clang, '-v'] + compile.get_target_flags(), check=False).returncode

  # Additional compiler flags that we treat as if they were passed to us on the
  # commandline
  if EMCC_CFLAGS := os.environ.get('EMCC_CFLAGS'):
    args += shlex.split(EMCC_CFLAGS)

  if DEBUG:
    logger.warning(f'invocation: {shlex.join(args)} (in {os.getcwd()})')

  # Strip args[0] (program name)
  args = args[1:]

  # Handle some global flags

  # read response files very early on
  try:
    args = substitute_response_files(args)
  except OSError as e:
    exit_with_error(e)

  if '--help' in args:
    # Documentation for emcc and its options must be updated in:
    #    site/source/docs/tools_reference/emcc.rst
    # This then gets built (via: `make -C site text`) to:
    #    site/build/text/docs/tools_reference/emcc.txt
    # This then needs to be copied to its final home in docs/emcc.txt from where
    # we read it here.  We have CI rules that ensure its always up-to-date.
    print(read_file(utils.path_from_root('docs/emcc.txt')))

    print('''
------------------------------------------------------------------

emcc: supported targets: llvm bitcode, WebAssembly, NOT elf
(autoconf likes to see elf above to enable shared object support)
''')
    return 0

  ## Process argument and setup the compiler
  state = EmccState(args)
  newargs = cmdline.parse_arguments(state.orig_args)

  if not shared.SKIP_SUBPROCS:
    shared.check_sanity()

  # Begin early-exit flag handling.

  if '--version' in args:
    print(cmdline.version_string())
    print('''\
Copyright (C) 2026 the Emscripten authors (see AUTHORS.txt)
This is free and open source software under the MIT license.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
''')
    return 0

  if '-dumpversion' in args: # gcc's doc states "Print the compiler version [...] and don't do anything else."
    print(utils.EMSCRIPTEN_VERSION)
    return 0

  if '-dumpmachine' in args or '-print-target-triple' in args or '--print-target-triple' in args:
    print(shared.get_llvm_target())
    return 0

  if '-print-search-dirs' in args or '--print-search-dirs' in args:
    print(f'programs: ={config.LLVM_ROOT}')
    print(f'libraries: ={cache.get_lib_dir(absolute=True)}')
    return 0

  if '-print-libgcc-file-name' in args or '--print-libgcc-file-name' in args:
    settings.limit_settings(None)
    compiler_rt = system_libs.Library.get_usable_variations()['libcompiler_rt']
    print(compiler_rt.get_path(absolute=True))
    return 0

  print_file_name = [a for a in args if a.startswith(('-print-file-name=', '--print-file-name='))]
  if print_file_name:
    libname = print_file_name[-1].split('=')[1]
    system_libpath = cache.get_lib_dir(absolute=True)
    fullpath = os.path.join(system_libpath, libname)
    if os.path.isfile(fullpath):
      print(fullpath)
    else:
      print(libname)
    return 0

  # End early-exit flag handling

  if 'EMMAKEN_NO_SDK' in os.environ:
    exit_with_error('EMMAKEN_NO_SDK is no longer supported.  The standard -nostdlib and -nostdinc flags should be used instead')

  if 'EMMAKEN_COMPILER' in os.environ:
    exit_with_error('`EMMAKEN_COMPILER` is no longer supported.\n' +
                    'Please use the `LLVM_ROOT` and/or `COMPILER_WRAPPER` config settings instead')

  if 'EMMAKEN_CFLAGS' in os.environ:
    exit_with_error('`EMMAKEN_CFLAGS` is no longer supported, please use `EMCC_CFLAGS` instead')

  if 'EMCC_REPRODUCE' in os.environ:
    options.reproduce = os.environ['EMCC_REPRODUCE']

  # For internal consistency, ensure we don't attempt to read or write any link time
  # settings until we reach the linking phase.
  settings.limit_settings(COMPILE_TIME_SETTINGS)

  phase_setup(state)

  if '-print-resource-dir' in args or any(a.startswith('--print-prog-name') for a in args):
    shared.exec_process([clang] + compile.get_cflags(tuple(args)) + args)
    assert False, 'exec_process should not return'

  if '--cflags' in args:
    # Just print the flags we pass to clang and exit.  We need to do this after
    # phase_setup because the setup sets things like SUPPORT_LONGJMP.
    cflags = compile.get_cflags(x for x in args if x != '--cflags')
    print(shlex.join(cflags))
    return 0

  if options.reproduce:
    create_reproduce_file(options.reproduce, args)

  if state.mode == Mode.POST_LINK_ONLY:
    if len(options.input_files) != 1:
      exit_with_error('--post-link requires a single input file')
    linker_args = separate_linker_flags(newargs)[1]
    linker_args = [f.value for f in linker_args]
    # Delay import of link.py to avoid processing this file when only compiling
    from tools import link  # noqa: PLC0415
    link.run_post_link(options.input_files[0], options, linker_args)
    return 0

  # Compile source code to object files
  # When only compiling this function never returns.
  linker_args = phase_compile_inputs(options, state, newargs)

  if state.mode == Mode.COMPILE_AND_LINK:
    # Delay import of link.py to avoid processing this file when only compiling
    from tools import link
    return link.run(options, linker_args)
  else:
    logger.debug('stopping after compile phase')
    return 0


def separate_linker_flags(newargs):
  """Process argument list separating out compiler args and linker args.

  - Linker flags include input files and are returned a list of LinkFlag objects.
  - Compiler flags are those to be passed to `clang -c`.
  """
  compiler_args = []
  linker_args = []

  def add_link_arg(flag, is_file=False):
    linker_args.append(LinkFlag(flag, is_file))

  skip = False
  for i in range(len(newargs)):
    if skip:
      skip = False
      continue

    arg = newargs[i]
    if arg in CLANG_FLAGS_WITH_ARGS:
      skip = True

    def get_next_arg():
      if len(newargs) <= i + 1:
        exit_with_error(f"option '{arg}' requires an argument")
      return newargs[i + 1]

    if not arg.startswith('-') or arg == '-':
      if not os.path.exists(arg) and arg != '-':
        exit_with_error('%s: No such file or directory ("%s" was expected to be an input file, based on the commandline arguments provided)', arg, arg)
      add_link_arg(arg, True)
    elif arg == '-z':
      add_link_arg(arg)
      add_link_arg(get_next_arg())
    elif arg.startswith('-Wl,'):
      for flag in arg.split(',')[1:]:
        add_link_arg(flag)
    elif arg == '-Xlinker':
      add_link_arg(get_next_arg())
    elif arg == '-s' or arg.startswith(('-l', '-L', '--js-library=', '-z', '-u')):
      add_link_arg(arg)
    elif not arg.startswith('-o') and arg not in {'-nostdlib', '-nostartfiles', '-nolibc', '-nodefaultlibs', '-s'}:
      # All other flags are for the compiler
      compiler_args.append(arg)
      if skip:
        compiler_args.append(get_next_arg())

  return compiler_args, linker_args


@ToolchainProfiler.profile_block('setup')
def phase_setup(state):
  """Second phase: configure and setup the compiler based on the specified settings and arguments."""
  has_header_inputs = any(get_file_suffix(f) in HEADER_EXTENSIONS for f in options.input_files)

  if options.post_link:
    state.mode = Mode.POST_LINK_ONLY
  elif has_header_inputs or options.dash_c or options.dash_S or options.syntax_only or options.dash_E or options.dash_M:
    state.mode = Mode.COMPILE_ONLY

  if state.mode == Mode.COMPILE_ONLY:
    for key in user_settings:
      if key not in COMPILE_TIME_SETTINGS:
        diagnostics.warning(
            'unused-command-line-argument',
            "linker setting ignored during compilation: '%s'" % key)
    for arg in state.orig_args:
      if arg in LINK_ONLY_FLAGS:
        diagnostics.warning(
            'unused-command-line-argument',
            "linker flag ignored during compilation: '%s'" % arg)

  if 'USE_PTHREADS' in user_settings:
    settings.PTHREADS = settings.USE_PTHREADS

  # Pthreads and Wasm Workers require targeting shared Wasm memory (SAB).
  if settings.PTHREADS or settings.WASM_WORKERS:
    settings.SHARED_MEMORY = 1

  if 'DISABLE_EXCEPTION_CATCHING' in user_settings and 'EXCEPTION_CATCHING_ALLOWED' in user_settings:
    # If we get here then the user specified both DISABLE_EXCEPTION_CATCHING and EXCEPTION_CATCHING_ALLOWED
    # on the command line.  This is no longer valid so report either an error or a warning (for
    # backwards compat with the old `DISABLE_EXCEPTION_CATCHING=2`
    if user_settings['DISABLE_EXCEPTION_CATCHING'] in {'0', '2'}:
      diagnostics.warning('deprecated', 'DISABLE_EXCEPTION_CATCHING=X is no longer needed when specifying EXCEPTION_CATCHING_ALLOWED')
    else:
      exit_with_error('DISABLE_EXCEPTION_CATCHING and EXCEPTION_CATCHING_ALLOWED are mutually exclusive')

  if settings.EXCEPTION_CATCHING_ALLOWED:
    settings.DISABLE_EXCEPTION_CATCHING = 0

  if settings.WASM_EXCEPTIONS:
    if user_settings.get('DISABLE_EXCEPTION_CATCHING') == '0':
      exit_with_error('DISABLE_EXCEPTION_CATCHING=0 is not compatible with -fwasm-exceptions')
    if user_settings.get('DISABLE_EXCEPTION_THROWING') == '0':
      exit_with_error('DISABLE_EXCEPTION_THROWING=0 is not compatible with -fwasm-exceptions')
    # -fwasm-exceptions takes care of enabling them, so users aren't supposed to
    # pass them explicitly, regardless of their values
    if 'DISABLE_EXCEPTION_CATCHING' in user_settings or 'DISABLE_EXCEPTION_THROWING' in user_settings:
      diagnostics.warning('emcc', 'you no longer need to pass DISABLE_EXCEPTION_CATCHING or DISABLE_EXCEPTION_THROWING when using Wasm exceptions')
    settings.DISABLE_EXCEPTION_CATCHING = 1
    settings.DISABLE_EXCEPTION_THROWING = 1

    if user_settings.get('ASYNCIFY') == '1':
      diagnostics.warning('emcc', 'ASYNCIFY=1 is not compatible with -fwasm-exceptions. Parts of the program that mix ASYNCIFY and exceptions will not compile.')

    if user_settings.get('SUPPORT_LONGJMP') == 'emscripten':
      exit_with_error('SUPPORT_LONGJMP=emscripten is not compatible with -fwasm-exceptions')

  if settings.DISABLE_EXCEPTION_THROWING and not settings.DISABLE_EXCEPTION_CATCHING:
    exit_with_error("DISABLE_EXCEPTION_THROWING was set (probably from -fno-exceptions) but is not compatible with enabling exception catching (DISABLE_EXCEPTION_CATCHING=0). If you don't want exceptions, set DISABLE_EXCEPTION_CATCHING to 1; if you do want exceptions, don't link with -fno-exceptions")

  if options.target.startswith('wasm64'):
    default_setting('MEMORY64', 1)

  if settings.MEMORY64 and options.target.startswith('wasm32'):
    exit_with_error('wasm32 target is not compatible with -sMEMORY64')

  # Wasm SjLj cannot be used with Emscripten EH
  if settings.SUPPORT_LONGJMP == 'wasm':
    # DISABLE_EXCEPTION_THROWING is 0 by default for Emscripten EH throwing, but
    # Wasm SjLj cannot be used with Emscripten EH. We error out if
    # DISABLE_EXCEPTION_THROWING=0 is explicitly requested by the user;
    # otherwise we disable it here.
    if user_settings.get('DISABLE_EXCEPTION_THROWING') == '0':
      exit_with_error('SUPPORT_LONGJMP=wasm cannot be used with DISABLE_EXCEPTION_THROWING=0')
    # We error out for DISABLE_EXCEPTION_CATCHING=0, because it is 1 by default
    # and this can be 0 only if the user specifies so.
    if user_settings.get('DISABLE_EXCEPTION_CATCHING') == '0':
      exit_with_error('SUPPORT_LONGJMP=wasm cannot be used with DISABLE_EXCEPTION_CATCHING=0')
    default_setting('DISABLE_EXCEPTION_THROWING', 1)

  # SUPPORT_LONGJMP=1 means the default SjLj handling mechanism, which is 'wasm'
  # if Wasm EH is used and 'emscripten' otherwise.
  if settings.SUPPORT_LONGJMP == 1:
    if settings.WASM_EXCEPTIONS:
      settings.SUPPORT_LONGJMP = 'wasm'
    else:
      settings.SUPPORT_LONGJMP = 'emscripten'


@ToolchainProfiler.profile_block('compile inputs')
def phase_compile_inputs(options, state, newargs):
  if shared.run_via_emxx:
    compiler = [shared.CLANG_CXX]
  else:
    compiler = [shared.CLANG_CC]

  if config.COMPILER_WRAPPER:
    logger.debug('using compiler wrapper: %s', config.COMPILER_WRAPPER)
    compiler.insert(0, config.COMPILER_WRAPPER)

  system_libs.ensure_sysroot()

  def get_clang_command():
    return compiler + compile.get_cflags(state.orig_args)

  def get_clang_command_preprocessed():
    return compiler + compile.get_clang_flags(state.orig_args)

  def get_clang_command_asm():
    return compiler + compile.get_target_flags()

  if state.mode == Mode.COMPILE_ONLY:
    if options.output_file and get_file_suffix(options.output_file) == '.bc' and not settings.LTO and '-emit-llvm' not in state.orig_args:
      diagnostics.warning('emcc', '.bc output file suffix used without -flto or -emit-llvm.  Consider using .o extension since emcc will output an object file, not a bitcode file')
    if all(get_file_suffix(i) in ASSEMBLY_EXTENSIONS for i in options.input_files):
      cmd = get_clang_command_asm() + newargs
    else:
      cmd = get_clang_command() + newargs
    shared.exec_process(cmd)
    assert False, 'exec_process should not return'

  # In COMPILE_AND_LINK we need to compile source files too, but we also need to
  # filter out the link flags
  assert state.mode == Mode.COMPILE_AND_LINK
  assert not options.dash_c
  compile_args, linker_args = separate_linker_flags(newargs)

  # Map of file basenames to how many times we've seen them.  We use this to generate
  # unique `_NN` suffix for object files in cases when we are compiling multiple sources that
  # have the same basename.  e.g. `foo/utils.c` and `bar/utils.c` on the same command line.
  seen_names = {}

  def uniquename(name):
    if name not in seen_names:
      # No suffix needed the first time we see given name.
      seen_names[name] = 1
      return name

    unique_suffix = '_%d' % seen_names[name]
    seen_names[name] += 1
    base, ext = os.path.splitext(name)
    return base + unique_suffix + ext

  def get_object_filename(input_file):
    objfile = unsuffixed_basename(input_file) + '.o'
    return in_temp(uniquename(objfile))

  def compile_source_file(input_file):
    logger.debug(f'compiling source file: {input_file}')
    output_file = get_object_filename(input_file)
    ext = get_file_suffix(input_file)
    if ext in ASSEMBLY_EXTENSIONS:
      cmd = get_clang_command_asm()
    elif ext in PREPROCESSED_EXTENSIONS:
      cmd = get_clang_command_preprocessed()
    else:
      cmd = get_clang_command()
      if ext == '.pcm':
        cmd = [c for c in cmd if not c.startswith('-fprebuilt-module-path=')]
    cmd += compile_args + ['-c', input_file, '-o', output_file]
    if options.requested_debug == '-gsplit-dwarf':
      # When running in COMPILE_AND_LINK mode we compile objects to a temporary location
      # but we want the `.dwo` file to be generated in the current working directory,
      # like it is under clang.  We could avoid this hack if we use the clang driver
      # to generate the temporary files, but that would also involve using the clang
      # driver to perform linking which would be a big change.
      cmd += ['-Xclang', '-split-dwarf-file', '-Xclang', unsuffixed_basename(input_file) + '.dwo']
      cmd += ['-Xclang', '-split-dwarf-output', '-Xclang', unsuffixed_basename(input_file) + '.dwo']
    shared.check_call(cmd)
    if not shared.SKIP_SUBPROCS:
      assert os.path.exists(output_file)
      if options.save_temps:
        shutil.copyfile(output_file, utils.unsuffixed_basename(input_file) + '.o')
    return output_file

  # Compile input files individually to temporary locations.
  for arg in linker_args:
    if not arg.is_file:
      continue
    input_file = arg.value
    file_suffix = get_file_suffix(input_file)
    if file_suffix in SOURCE_EXTENSIONS | ASSEMBLY_EXTENSIONS or (options.dash_c and file_suffix == '.bc'):
      arg.value = compile_source_file(input_file)
    elif file_suffix in DYLIB_EXTENSIONS:
      logger.debug(f'using shared library: {input_file}')
    elif building.is_ar(input_file):
      logger.debug(f'using static library: {input_file}')
    elif options.input_language:
      arg.value = compile_source_file(input_file)
    elif input_file == '-':
      exit_with_error('-E or -x required when input is from standard input')
    else:
      # Default to assuming the inputs are object files and pass them to the linker
      pass

  return [f.value for f in linker_args]


if __name__ == '__main__':
  try:
    sys.exit(main(sys.argv))
  except KeyboardInterrupt:
    logger.debug('KeyboardInterrupt')
    sys.exit(1)