build/go/go_fuzzer.gni

# Copyright 2019 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/fuzzing/fuzzer.gni")
import("//build/go/go_build.gni")
import("//build/go/go_library.gni")

nl = "$0x0a"  # newline character

go_fuzzer_wrapper_template =
    "// Code generated by //build/go/go_fuzzer.gni; DO NOT EDIT.${nl}${nl}" +
    "//line //build/go/go_fuzzer_wrapper.go:1${nl}" +
    read_file("//build/go/go_fuzzer_wrapper.go", "string")

# Defines a Go fuzz target.
#
#   gopackage (required)
#     The Go package exporting the target function.
#
#   gofunction (optional, default: "Fuzz")
#     The name of the exported target function.
#
#   deps (required)
#     List of labels representing go_library targets this target depends on.
#
# Additionally, the `cmx`, `dictionary`, and `options` parameters
# defined for `fuzzer` are supported.

template("go_fuzzer") {
  assert(defined(invoker.gopackage),
         "gopackage must be defined for $target_name")
  assert(defined(invoker.deps), "deps must be defined for $target_name")

  fuzzer_name = target_name
  gopackage = invoker.gopackage
  gofunction = "Fuzz"
  if (defined(invoker.gofunction)) {
    gofunction = invoker.gofunction
  }

  # Building a Go fuzzer involves a few steps:
  # 1. Generate the wrapper source file.
  source = go_fuzzer_wrapper_template
  source = string_replace(source, "GO_FUZZER_PKG", gopackage)
  source = string_replace(source, "GO_FUZZER_FUNC", gofunction)
  wrapper_name = "${fuzzer_name}_wrapper"
  source_name = "${wrapper_name}.go"
  write_file("$target_gen_dir/$source_name", source)

  # 2. Define a go_library rule containing that source file.
  library_name = "${wrapper_name}_library"
  go_library(library_name) {
    name = wrapper_name
    source_dir = target_gen_dir
    sources = [ source_name ]
    forward_variables_from(invoker, [ "deps" ])
  }

  # 3a. Build the wrapper package as a C archive with Go's libfuzzer instrumentation.
  go_build(wrapper_name) {
    gopackages = [ wrapper_name ]
    carchive = true
    tags = [ "libfuzzer" ]
    gcflags = [ "all=-d=libfuzzer" ]
    deps = [ ":$library_name" ]
  }

  # 3b. Alternately, create a fuzzer unit test to ensure fuzzer code is built even when not fuzzing.
  test_wrapper_name = "${fuzzer_name}_test_wrapper"
  go_build(test_wrapper_name) {
    gopackages = [ wrapper_name ]
    carchive = true
    deps = [ ":$library_name" ]
  }

  # 4. Link the resulting C archive as though it was a normal C++ fuzzer.
  fuzzer(fuzzer_name) {
    forward_variables_from(invoker,
                           [
                             "cmx",
                             "dictionary",
                             "options",
                           ])

    # Examine the toolchain configs to detect if it is being built as part of a fuzzer variant.
    # If not, the fuzzer unit test will be built instead.
    fuzzer_configs = [ "//build/config/sanitizers:fuzzer" ]
    if (toolchain_variant.configs + fuzzer_configs - fuzzer_configs ==
        toolchain_variant.configs) {
      wrapper_name = test_wrapper_name
    }

    # As noted in go_build.gni, Go libraries do not generate distinct outputs for each variants,
    # but always use the output of the base toolchain.
    deps = [ ":${wrapper_name}(${toolchain_variant.base})" ]
    base_root_out_dir = get_label_info(deps[0], "root_out_dir")
    base_library_name = get_label_info(deps[0], "name")
    libs = [ "$base_root_out_dir/${base_library_name}.a" ]
  }
}