build/toolchain/wasm.gni

# Copyright (c) 2013 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import("//build/toolchain/ccache.gni")
import("//build/toolchain/gcc_toolchain.gni")

# Defines the configuration of emscripten for building WASM targets.

declare_args() {
  # The location of an activated embedded emsdk.
  emsdk_dir = rebase_path("//flutter/prebuilts/emsdk")

  wasm_use_pthreads = false
  wasm_use_dwarf = false
}

em_config_path = "$emsdk_dir/.emscripten"

if (use_ccache) {
  # ccache only supports compilation, not linking.
  compiler_prefix = "ccache "
} else {
  compiler_prefix = ""
}

template("wasm_toolchain") {
  gcc_toolchain(target_name) {
    extra_toolchain_args = {
      if (defined(invoker.extra_toolchain_args)) {
        forward_variables_from(invoker.extra_toolchain_args, "*")
      }
    }

    # emsdk_dir and em_config are defined in wasm.gni.
    ar = "$emsdk_dir/upstream/emscripten/emar --em-config $em_config_path"
    cc = "$compiler_prefix$emsdk_dir/upstream/emscripten/emcc --em-config $em_config_path"
    cxx = "$compiler_prefix$emsdk_dir/upstream/emscripten/em++ --em-config $em_config_path"
    asm = "$emsdk_dir/upstream/emscripten/emcc --em-config $em_config_path"

    # emscripten emits this .worker.js file conditionally depending on whether
    # pthreads are on or not. Unfortunately, there is no way to conditionally
    # change the outputs of the toolchain depending on flags that are specified
    # in the target or configs. In order to resolve this, we will always
    # specify the .worker.js file as an output, and touch the path to create a
    # dummy file. If the target does use pthreads, this dummy file will be
    # overwritten. If the target does not, the dummy file will satisfy the
    # toolchain's requirement that it has this as an output.
    ld = "$emsdk_dir/upstream/emscripten/em++ --em-config $em_config_path"
    readelf = "readelf"
    nm = "nm"

    toolchain_cpu = "wasm"
    toolchain_os = "wasm"

    is_clang = true

    link_outputs = [
      "{{root_out_dir}}/{{target_output_name}}.wasm",

      # We always output a symbol map.
      "{{root_out_dir}}/{{target_output_name}}.js.symbols",
    ]

    if (is_debug && !wasm_use_dwarf) {
      link_outputs += [ "{{root_out_dir}}/{{target_output_name}}.wasm.map" ]
    }
  }
}

# Defines a WASM library target.
# Args:
#  export_name: The public name of the module to expose (EXPORT_NAME for
#               emscripten).  Defaults to target_name.
template("wasm_lib") {
  export_name = target_name
  if (defined(invoker.export_name)) {
    export_name = invoker.export_name
  }

  _target_ldflags = [
    # This is to prevent that two different wasm modules end up generating
    # JS that overrides the same global variable (var Module = ...)
    "-s",
    "EXPORT_NAME=${export_name}",
  ]

  if (defined(invoker.ldflags)) {
    _target_ldflags += invoker.ldflags
  }

  _target_cflags = [
    "-s",
    "MAIN_MODULE=1",
  ]

  if (defined(invoker.cflags)) {
    _target_cflags += invoker.cflags
  }

  _vars_to_forward = [
    "defines",
    "deps",
    "includes",
    "inputs",
    "sources",
    "include_dirs",
    "public_configs",
    "testonly",
    "visibility",
  ]

  _lib_name = target_name

  executable("$_lib_name") {
    forward_variables_from(invoker, _vars_to_forward)
    cflags = _target_cflags
    ldflags = _target_ldflags
    output_extension = "js"
  }
}