build: Add OpenWrt toolchains

src/build/config/BUILDCONFIG.gn

@@ -264,6 +264,8 @@ if (target_os == "android") {
   _default_toolchain = "//build/toolchain/aix:$target_cpu"
 } else if (target_os == "zos") {
   _default_toolchain = "//build/toolchain/zos:$target_cpu"
+} else if (target_os == "openwrt") {
+  _default_toolchain = "//build/toolchain/openwrt:$target_cpu"
 } else {
   assert(false, "Unsupported target_os: $target_os")
 }
@@ -298,7 +300,7 @@ is_android = current_os == "android"
 is_chromeos = current_os == "chromeos"
 is_fuchsia = current_os == "fuchsia"
 is_ios = current_os == "ios"
-is_linux = current_os == "linux"
+is_linux = current_os == "linux" || current_os == "openwrt"
 is_mac = current_os == "mac"
 is_nacl = current_os == "nacl"
 is_win = current_os == "win" || current_os == "winuwp"

src/build/config/compiler/BUILD.gn

@@ -275,6 +275,9 @@ config("compiler") {
     if (is_chromeos) {
       configs += [ "//build/config/chromeos:compiler" ]
     }
+    if (current_os == "openwrt") {
+      configs += [ "//build/config/openwrt:compiler" ]
+    }
   } else if (is_nacl) {
     configs += [ "//build/config/nacl:compiler" ]
   } else if (is_mac) {
@@ -917,7 +920,7 @@ config("compiler_cpu_abi") {
         ]
       }
     } else if (current_cpu == "arm") {
-      if (is_clang && !is_android && !is_nacl) {
+      if (is_clang && !is_android && !is_nacl && current_os != "openwrt") {
         cflags += [ "--target=arm-linux-gnueabihf" ]
         ldflags += [ "--target=arm-linux-gnueabihf" ]
       }
@@ -935,7 +938,7 @@ config("compiler_cpu_abi") {
         cflags += [ "-mtune=$arm_tune" ]
       }
     } else if (current_cpu == "arm64") {
-      if (is_clang && !is_android && !is_nacl && !is_fuchsia) {
+      if (is_clang && !is_android && !is_nacl && !is_fuchsia && current_os != "openwrt") {
         cflags += [ "--target=aarch64-linux-gnu" ]
         ldflags += [ "--target=aarch64-linux-gnu" ]
       }
@@ -948,7 +951,7 @@ config("compiler_cpu_abi") {
       }
     } else if (current_cpu == "mipsel" && !is_nacl) {
       ldflags += [ "-Wl,--hash-style=sysv" ]
-      if (custom_toolchain == "") {
+      if (custom_toolchain == "" && current_os != "openwrt") {
         if (is_clang) {
           if (is_android) {
             cflags += [ "--target=mipsel-linux-android" ]
@@ -1085,7 +1088,7 @@ config("compiler_cpu_abi") {
     } else if (current_cpu == "mips64el") {
       cflags += [ "-D__SANE_USERSPACE_TYPES__" ]
       ldflags += [ "-Wl,--hash-style=sysv" ]
-      if (custom_toolchain == "") {
+      if (custom_toolchain == "" && current_os != "openwrt") {
         if (is_clang) {
           if (is_android) {
             cflags += [ "--target=mips64el-linux-android" ]

src/build/config/openwrt/BUILD.gn

@@ -0,0 +1,64 @@
+# Copyright 2014 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/config/c++/c++.gni")
+import("//build/config/compiler/compiler.gni")
+import("//build/config/sanitizers/sanitizers.gni")
+
+if (current_toolchain == default_toolchain) {
+  import("//build/toolchain/concurrent_links.gni")
+}
+
+assert(current_os == "openwrt")
+
+declare_args() {
+  build_static = false
+}
+
+# This is included by reference in the //build/config/compiler config that
+# is applied to all targets. It is here to separate out the logic that is
+# Android-only.
+config("compiler") {
+  cflags = []
+  ldflags = []
+
+  defines = [
+    "_LIBCPP_HAS_MUSL_LIBC",
+    "__UCLIBC__",
+    "__MUSL__",
+  ]
+
+  if (build_static) {
+    # Musl static objects are not built with -fPIC, cannot use -static-pie.
+    ldflags += [ "-static" ]
+  } else if (current_cpu == "x86") {
+    ldflags += [ "-Wl,--dynamic-linker=/lib/ld-musl-i386.so.1" ]
+  } else if (current_cpu == "mipsel") {
+    ldflags += [ "-Wl,--dynamic-linker=/lib/ld-musl-mipsel-sf.so.1" ]
+  }
+
+  abi = "musl"
+  if (current_cpu == "arm") {
+    abi = "muslgnueabi"
+    arch = "arm"
+  } else if (current_cpu == "arm64") {
+    arch = "aarch64"
+  } else if (current_cpu == "x86") {
+    arch = "i486"
+  } else if (current_cpu == "x64") {
+    arch = "x86_64"
+  } else if (current_cpu == "mipsel") {
+    arch = "mipsel"
+  } else if (current_cpu == "mips64el") {
+    arch = "mips64el"
+  } else {
+    assert(false, "Architecture not supported")
+  }
+  cflags += [ "--target=$arch-openwrt-linux-$abi" ]
+  ldflags += [ "--target=$arch-openwrt-linux-$abi" ]
+
+  # Assign any flags set for the C compiler to asmflags so that they are sent
+  # to the assembler.
+  asmflags = cflags
+}

src/build/toolchain/openwrt/BUILD.gn

@@ -0,0 +1,15 @@
+# Copyright 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/config/sysroot.gni")
+import("//build/toolchain/gcc_toolchain.gni")
+
+assert(target_os == "openwrt")
+
+clang_toolchain(target_cpu) {
+  toolchain_args = {
+    current_cpu = target_cpu
+    current_os = "openwrt"
+  }
+}