build/toolchain/ifs_shared_library.gni

# Copyright 2021 The Fuchsia 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/zircon/clang.gni")

_llvm_ifs = "$clang_tool_dir/llvm-ifs"

# Define a linkable shared library built from a text ABI (.ifs) specification.
#
# This uses a `.ifs` file kept in the source tree to create a linkable ELF
# shared library stub file.  This can be used at link time to build executable
# and (non-stub) shared library binaries without reference to the actual
# runtime shared library.  The real (non-stub) shared library to be used at
# runtime must be compiled separately and included at runtime as necessary.
# This target only takes care of satisfying any link-time dependencies.
# Its label is used in `deps` like a shared_library() target.
#
# This defines two public targets and a config.  The main target acts like
# shared_library() for linking purposes, but is not a GN target with outputs.
# An additional target "$target_name.stub" is defined whose outputs include the
# linking stub ELF file itself, e.g. for use as input to a copy() target or the
# like.  The "$target_name.config" config is defined to make `-l$output_name`
# implicit link arguments work by supplying a `lib_dirs` that will find the
# stub and nothing else.  This config is propagated from the main target via
# public_configs, but this alone may not be sufficient for it to reach the
# linking targets unless all the intervening deps are via public_deps.
#
# Parameters
#
#   * abi
#     - Required: Source path to a `.ifs` file defining the library's ELF ABI.
#     - Type: file
#
#   * output_name
#     - Optional: The plain name of the linkable library file to write,
#     without the `lib` prefix or the `.so` extension.
#     - Type: string
#     - Default: $target_name
#
#   * public, public_configs, public_deps
#     - Optional: As for shared_library().
#
template("ifs_shared_library") {
  main_target = target_name
  stub_target = "$target_name.stub"
  config_target = "$target_name.config"

  gen_target = "_ifs_shared_library.$target_name.$clang_cpu"
  gen_label = ":$gen_target($default_toolchain)"
  gen_dir =
      get_label_info(gen_label, "target_gen_dir") + "/$target_name.$clang_cpu"

  if (defined(invoker.output_name)) {
    output_name = invoker.output_name
  } else {
    output_name = target_name
  }

  gen_stub_file = "$gen_dir/lib$output_name.so"
  public_stub_file = "$root_out_dir/lib$output_name.so"

  source_set(main_target) {
    public_configs = []
    forward_variables_from(invoker,
                           [
                             "visibility",
                             "public",
                             "public_configs",
                             "public_deps",
                             "testonly",
                           ])
    public_configs += [ ":$config_target" ]
    libs = [ gen_stub_file ]
    deps = [ gen_label ]
  }

  config(config_target) {
    forward_variables_from(invoker,
                           [
                             "visibility",
                             "testonly",
                           ])
    if (defined(visibility)) {
      visibility += [ ":$main_target" ]
    }
    lib_dirs = [ gen_dir ]
  }

  copy(stub_target) {
    forward_variables_from(invoker,
                           [
                             "visibility",
                             "testonly",
                           ])
    deps = [ gen_label ]
    sources = [ gen_stub_file ]
    outputs = [ public_stub_file ]
  }

  if (current_toolchain == default_toolchain) {
    action(gen_target) {
      forward_variables_from(invoker,
                             [
                               "visibility",
                               "testonly",
                             ])
      if (defined(visibility)) {
        visibility += [
          ":$main_target",
          ":$stub_target",
        ]
      }

      # Output timestamps are not freshened if contents do not change.
      all_outputs_fresh = false

      script = _llvm_ifs
      sources = [ invoker.abi ]
      outputs = [ gen_stub_file ]
      args = [
        "--input-format=IFS",
        "--arch=${clang_cpu}",
        "--endianness=little",
        "--bitwidth=64",
        "--write-if-changed",
        "--output-elf=" + rebase_path(gen_stub_file, root_build_dir),
        rebase_path(invoker.abi, root_build_dir),
      ]
    }
  } else {
    not_needed(invoker, [ "abi" ])
  }
}